A butt hinge is the standard mortised door hinge used in virtually every residential and commercial building in North America. Two rectangular leaves are recessed flush into the door edge and frame, joined by an exposed knuckle and pin at the centerline. Butt hinges are available as plain bearing, ball bearing, or spring-loaded variants, in sizes from 3.5" to 5" or larger, and in materials including steel, stainless steel, brass, and bronze. This guide covers anatomy, sizing, material selection, fire code requirements per NFPA 80, NRP security considerations, and step-by-step installation.
| Type | Two-leaf mortised hinge with knuckle and pin |
|---|---|
| Bearing Types | Plain bearing, ball bearing, spring-loaded |
| Key Standard | ANSI/BHMA A156.1 (Butts and Hinges) |
| Fire Code | Min. 4.5" ball bearing steel hinge per NFPA 80 |
| Common Sizes | 3.5", 4", 4.5", 5" (height × width) |
| Hinge Count | 2 per residential door; 3+ per commercial/fire door |
| Security Option | NRP (Non-Removable Pin) for outswing doors |
| Materials | Steel, stainless steel (304/316), brass, bronze |
| Weight Ratings | Standard: up to 75 lbs; Heavy duty: up to 200+ lbs per pair |
| Last Updated | 2026-03-01 |
A butt hinge is the most widely used door hinge in the world. Its name derives from the installation method: the two leaves “butt” against each other when the door is closed, with both leaves recessed (mortised) flush into the door edge and the door frame so that only the knuckle protrudes at the hinge line. This mortised installation gives the door a clean appearance and provides a tight, gap-free fit between door and frame.
The butt hinge has been the standard for door hanging since the 17th century and remains dominant today because of its simplicity, load capacity, and compatibility with standard mortised door frames. Every major door manufacturer, frame fabricator, and hardware supplier references butt hinge dimensions as the baseline for door hardware coordination. Understanding butt hinges thoroughly is foundational to specifying and installing any door assembly correctly.
A butt hinge consists of five functional components, each with a specific role in the assembly's load-carrying capacity and service life:
The two flat rectangular plates that attach to the door edge and frame are called leaves (singular: leaf). Each leaf contains a row of countersunk screw holes for fastening, and a series of barrel sections (called knuckle sections or loops) along one edge that interlock with the barrel sections of the opposite leaf. The leaf dimensions — height by width — define the nominal hinge size (e.g., 4.5" × 4.5"). Leaf thickness ranges from approximately 0.090" for light-duty residential hinges to 0.180" or more for heavy commercial hinges, directly affecting stiffness and load rating.
The knuckle is the cylindrical assembly formed by the interlocking barrel sections of the two leaves. When assembled with the pin, the knuckle is the pivot around which the door rotates. Knuckle geometry and the number of knuckle sections (typically 3 or 5) affect hinge strength, the distribution of bearing load along the pin, and the appearance of the hinge profile. A 5-knuckle hinge distributes load over more bearing surfaces and presents a more refined visual profile than a 3-knuckle version.
The pin passes through all interlocked barrel sections to complete the knuckle assembly and allow rotation. On standard butt hinges the pin is removable — it can be tapped out from the bottom when the door is open. This is convenient for door removal during installation but creates a security vulnerability on outswing doors (see NRP section below). Pin diameter correlates with hinge size and load rating; heavy-duty hinges use thicker, hardened steel pins for greater shear strength.
Ball bearing hinges incorporate precision-ground steel ball bearings between the knuckle sections, positioned to carry radial load and reduce rotational friction. Bearings are typically held in a race (a thin retaining ring) and are sealed or packed with grease from the factory. The bearing count per hinge varies by hinge size and manufacturer. Ball bearings are the defining characteristic of commercial-grade hinges and are required by ANSI/BHMA A156.1 for Grade 1 applications.
The visible end cap at the top and bottom of the knuckle is called the tip or finial. Standard tips are flat (button tip) or slightly rounded. Decorative applications may use hospital tip, steeple tip, or ball tip designs. The tip style is primarily aesthetic but can affect whether the hinge complies with hospital or cleanroom specifications that require tips without crevices where bacteria can accumulate.
Plain bearing hinges rely on direct metal-to-metal contact between the interlocking knuckle sections. The pin rotates within the barrel with no rolling elements to reduce friction. This design is adequate for light residential doors operated a modest number of times per day, but metal-on-metal sliding contact wears progressively under load and frequency. Plain bearing hinges are not recommended for commercial applications, heavy doors, or any installation exceeding approximately 50 cycles per day. They are the standard specification for interior residential doors, closet doors, and cabinet doors where simplicity and low cost outweigh long service-life requirements.
Ball bearing hinges are the commercial and architectural standard. Precision steel balls between the knuckle sections convert sliding friction into rolling friction, reducing the effort required to open the door and extending hinge life dramatically. Ball bearing hinges are required by ANSI/BHMA A156.1 Grade 1 for commercial applications and by NFPA 80 for fire-rated doors. They are also the correct choice for any heavy door (over 50 lbs), high-frequency application (over 50 cycles per day), or installation where long, maintenance-free service life is a priority. Ball bearing hinges typically carry a rated life of 1,000,000 cycles when manufactured to Grade 1 tolerances.
Spring hinges are butt hinges with an integrated coil spring inside the barrel that returns the door to the closed position after each use. A tension adjustment mechanism (a pinhole or slot in the barrel) allows the spring tension to be set in the field. Spring hinges provide the simplest self-closing solution and are an economical option for light residential doors on accessible routes, pool gates, and interior fire-rated doors where ADA closing-speed compliance is not required. They do not provide hydraulic speed control, so unmodified spring hinges can close quickly and may not comply with ADA requirements for minimum closing time. For detailed coverage, see our Self-Closing Hinges guide.
Olive knuckle hinges are a decorative variant with an elongated, barrel-shaped knuckle that gives a more refined architectural appearance. They function identically to standard butt hinges but are specified when aesthetics are a priority. Wrap-around hinges add additional material that wraps around the door edge for added strength in applications where mortising depth is limited, such as thin cabinet doors or lightweight hollow-core doors.
Hinge sizing is determined by three variables: door height, door width, and door weight. The following table reflects ANSI/BHMA A156.1 and NFPA 80 sizing guidance for standard wood and steel doors:
| Hinge Size | Max Door Width | Max Door Weight (per pair) | Typical Application |
|---|---|---|---|
| 3.5" × 3.5" | Up to 32" | Up to 50 lbs | Interior residential, lightweight hollow-core |
| 4" × 4" | Up to 36" | Up to 75 lbs | Residential entry, solid-core interior |
| 4.5" × 4.5" | Up to 36" | Up to 85 lbs | Commercial standard; fire-rated doors per NFPA 80 |
| 5" × 4.5" | Up to 42" | Up to 150 lbs | Heavy commercial, oversized doors |
| 5" × 5" | Up to 48" | Up to 200+ lbs | Heavy-duty commercial, industrial, blast-resistant |
NFPA 80 Minimum Requirement: Fire-rated door assemblies require a minimum 4.5" × 4.5" steel or stainless steel ball bearing butt hinge. Hinges must carry a UL listing for the fire-rating duration of the assembly. For doors exceeding 90" in height or 200 lbs in weight per pair, 5" hinges are required.
The number of hinges required per door leaf depends on door height and intended use:
NFPA 80 (Standard for Fire Doors and Other Opening Protectives) specifies minimum hinge requirements by door size and weight for fire-rated assemblies. The following summarizes key sizing thresholds:
| Door Height | Door Width | Door Weight (pair) | Min. Hinge Size | Min. Hinge Qty |
|---|---|---|---|---|
| Up to 60" | Up to 36" | Up to 200 lbs | 4.5" × 4.5" | 2 |
| 61"–90" | Up to 36" | Up to 200 lbs | 4.5" × 4.5" | 3 |
| 91"–120" | Up to 36" | Up to 200 lbs | 4.5" × 4.5" | 4 |
| Up to 90" | 37"–48" | Over 200 lbs | 5" × 4.5" | 3 |
| Over 90" | Any | Any | 5" × 5" | 4+ |
All hinges on a fire-rated door assembly must be steel or stainless steel and must carry a UL listing covering the fire-rating duration of the assembly. Mixing hinge sizes or types on a single fire-rated door is not permitted under NFPA 80.
Standard steel hinges are the most economical option. They are suitable for interior doors in climate-controlled environments where corrosion is not a concern. Steel hinges are typically supplied primed for paint or with a zinc electroplate finish. They should not be used in exterior or high-humidity locations without additional corrosion protection. Steel is the required base material for fire-rated door assemblies per NFPA 80.
Stainless steel butt hinges are the premier choice for exterior applications, coastal environments, food service facilities, hospitals, and any location with elevated moisture or chemical exposure. Grade 304 stainless offers excellent corrosion resistance in most environments. Grade 316 adds molybdenum to the alloy for superior resistance to chloride attack, making it the specification standard for marine, waterfront, and salt-air environments. Stainless steel hinges are also specified for cleanroom and pharmaceutical facilities where outgassing, particulate generation, or surface contamination must be minimized.
Solid brass butt hinges are primarily specified for architectural and decorative applications where a traditional, warm appearance is required. Brass offers good corrosion resistance in most environments and is the traditional material for high-end residential entry doors, historic restoration projects, and architectural millwork. Brass hinges are available in polished brass, satin brass, antique brass, and related specialty finishes. Note that brass is softer than steel, so brass hinges are not appropriate for heavy commercial doors or high-abuse environments.
Bronze butt hinges (typically silicon bronze or architectural bronze) are specified for coastal and marine applications requiring outstanding corrosion resistance, and for architectural projects where a distinctive patinating finish is desired. Silicon bronze is extremely resistant to saltwater corrosion and is common in marina, shipbuilding, and coastal construction applications. Bronze hinges are heavier and more expensive than steel or brass alternatives but provide exceptional longevity in demanding environments.
Butt hinge weight ratings reflect the maximum door weight the hinge pair is designed to support over its rated service life. Understanding this distinction prevents premature failure and ensures code compliance:
Standard weight hinges are designed for residential and light commercial doors. Plain bearing 3.5" and 4" hinges fall in this category. They are appropriate for hollow-core or lightweight solid-core interior doors in homes, apartments, and light commercial spaces where door frequency is moderate. Standard weight hinges typically carry a Grade 2 or Grade 3 ANSI/BHMA rating.
The 4.5" ball bearing hinge is the commercial standard. It supports doors in the 85–100 lb range (per leaf), which covers the majority of commercial hollow metal and solid wood doors. Grade 1 ANSI/BHMA ball bearing hinges in 4.5" size are required for fire-rated assemblies and specified on most commercial projects. They offer a rated service life of 1,000,000 cycles.
Heavy-duty hinges use 5" leaves, thicker leaf material, and larger-diameter ball bearings to handle the loads imposed by oversized, heavy, or high-security doors. Applications include hospital doors (which must accommodate stretchers and equipment and are subject to extremely high cycle counts), industrial facility doors, blast-resistant assemblies, and oversized architectural entries. Heavy-duty hinges may also carry a wider leaf width (e.g., 5" × 5") to provide a larger mortise contact area for shear resistance.
In residential construction, plain bearing 3.5" hinges cover most interior door applications. Entry doors and solid-core interior doors benefit from 4" ball bearing hinges for improved durability and smoother operation. Residential installation typically uses 2 hinges per door on doors up to 60" tall, or 3 hinges on taller doors or heavier doors. Finish selection for residential applications is primarily driven by aesthetics: satin nickel, oil-rubbed bronze, and matte black are common architectural finishes that coordinate with door handles and locks.
Exterior residential doors should use either stainless steel or solid brass hinges, not painted steel or zinc-plated hinges, which will corrode when exposed to weather. Many residential door slabs are pre-mortised at the factory for 3.5" × 3.5" hinges; upgrading to 4" requires either custom mortising or the use of a 4" hinge on the existing 3.5" mortise (which leaves a gap — not recommended).
Commercial applications require ball bearing hinges in a minimum 4.5" size, with Grade 1 ANSI/BHMA rating. Three hinges per door is standard, with four or more required on tall or heavy assemblies. Commercial doors are pre-templated at standard hinge locations: top hinge 5" down from the top of the door, bottom hinge 10" up from the bottom, and intermediate hinges evenly spaced. Steel hollow metal frames are pre-punched at these locations from the factory, as are standard commercial door slabs.
Commercial hinge selection must also address door hand (the direction of swing), door thickness (standard 1-3/4" commercial doors use wider leaf hinges than residential doors), and whether the installation requires concealed or surface-mounted fasteners for aesthetic or security reasons.
Fire-rated door assemblies present the most demanding and most code-specific requirements for butt hinge selection. NFPA 80 is the governing standard in the United States for all fire-rated door and frame assemblies, and it specifies hinge requirements in detail.
Every hinge on a fire-rated door assembly must carry a UL listing (or equivalent recognized testing laboratory listing) appropriate for the fire-rating duration of the assembly. Fire-rating durations include 20-minute, 45-minute, 60-minute, 90-minute, and 3-hour ratings. A hinge listed for a 3-hour assembly is suitable for any lower-rated assembly; a hinge listed only for 45-minute service cannot be used on a 90-minute assembly. The UL listing number must be traceable through the manufacturer's product documentation.
NFPA 80 restricts fire-rated door hinges to steel or stainless steel. Brass, bronze, and aluminum hinges are not permitted on fire-rated assemblies because these materials lose structural integrity at lower temperatures than steel. This restriction applies to the leaves, knuckle, pin, and all fasteners. Decorative steel hinges with applied finishes (e.g., brushed nickel plate over steel, oil-rubbed bronze coating on steel) may be acceptable if the underlying material is steel and the product carries an appropriate UL listing — verify with the listing documentation.
As tabulated above, NFPA 80 requires a minimum 4.5" × 4.5" ball bearing butt hinge for most fire-rated assemblies, with a minimum of three hinges per door leaf. This minimum increases with door height, width, and weight. Using non-conforming undersized hinges or insufficient hinge count on a fire-rated door is a code violation that will be flagged during Authority Having Jurisdiction (AHJ) inspection and may require door removal and reinstallation.
NFPA 80 requires that all fire-rated doors include a listed self-closing device. This can be satisfied by using self-closing (spring or hydraulic) butt hinges that carry the appropriate UL listing, or by a separate surface-mounted door closer. When using spring butt hinges on a fire-rated assembly, ensure the hinges are UL-listed for the specific fire rating of the assembly. Waterson's self-closing hinge line is UL-listed for 3-hour fire-rated assemblies and satisfies the NFPA 80 self-closing requirement without a separate closer device.
Standard butt hinges have a removable pin — tapped out from the bottom of the knuckle, the pin releases and the door can be lifted off its hinges regardless of whether the lockset is engaged. This presents a serious security vulnerability for outswing doors (doors that swing outward toward the exterior), because an intruder can remove the pin while the door is open slightly and then lift the door off its hinges from the exterior side even if the lock is engaged.
Non-Removable Pin hinges address this vulnerability through one of two mechanisms. The first is a set screw through the barrel wall that threads into a groove on the pin shaft, preventing the pin from being tapped out. The set screw is accessible only when the door is open; with the door closed and locked, the set screw is hidden and inaccessible. The second mechanism replaces the removable pin with a fixed, swaged, or welded pin that cannot be extracted without destroying the hinge.
Some manufacturers address the same vulnerability with a security stud: a small pin or lug on one leaf that engages a hole in the opposite leaf when the door closes. Even if the main pin is removed, the security stud keeps the hinge halves interlocked. Security stud designs allow the main pin to remain removable for installation convenience while preventing the door from being lifted off in use.
The International Building Code (IBC) and many security standards require NRP hinges on all outswing doors in commercial buildings. Outswing doors are common on exterior applications where weather-stripping compression against the frame face is desired, and on high-security applications where a door that opens into a secured area must resist forced entry from the exterior. Always specify NRP butt hinges on any outswing exterior door in a commercial building, or wherever the hinge knuckles are accessible from the unsecured side.
The standard butt hinge installation method is mortised: a shallow rectangular pocket is routed or chiseled into both the door edge and the frame hinge jamb so that each leaf sits flush with the surface. When the door is closed, the gap between door and frame is minimal and the leaf is not exposed. Mortised installation requires precision — the mortise must be exactly the depth of the leaf thickness, and the hinge must be located accurately so the door hangs level and swings freely without rubbing. Pre-machined commercial door slabs and pre-punched hollow metal frames eliminate field layout errors by locating mortises at standardized positions.
Surface-mounted butt hinges are attached directly to the face of the door and frame without mortising. They are visible on both surfaces and create a gap equal to the combined thickness of both leaves when the door is closed. Surface mounting is used when mortising is not practical (e.g., retrofit on a metal door that cannot be routed), on thin doors where mortise depth would compromise structural integrity, or in utility and industrial applications where appearance is not a concern. Some decorative designs intentionally use surface-mounted butt hinges as an architectural feature. Surface-mounted hinges on fire-rated assemblies are only permissible if the hinge model carries a specific UL listing for surface mounting on fire-rated assemblies.
Door sag — where the latch side of the door drops over time — is the most common butt hinge failure mode. It is caused by undersized hinges, insufficient screw engagement in the frame (particularly in hollow metal frames with only thin steel to engage), or mortises cut too deep on one leaf. Solutions include replacing undersized hinges with a larger or heavier-duty model, using longer screws that engage the structural wall framing rather than just the door jamb, or adding a hinge bolt or security stud to provide additional support. On wood frames, stripped screw holes can be repaired with wood filler or a slightly larger screw diameter.
Squeaking is caused by friction in the knuckle, typically on plain bearing hinges where the metal surfaces dry out or develop surface oxidation. The simplest solution is lubrication: apply a small amount of petroleum jelly, white lithium grease, or a dry PTFE lubricant to the pin and knuckle sections. Avoid WD-40 as a long-term lubricant — it is a water displacer and will wash away quickly, leaving the metal surfaces unprotected. For chronic squeaking on a frequently used door, replace plain bearing hinges with ball bearing models.
If the door rubs the hinge-side frame (the jamb), the hinge mortises may be too deep, causing the door to swing inward relative to the frame opening. Correct by adding a thin cardboard or plastic shim behind the hinge leaf in the mortise to bring the hinge out. If the door rubs the latch-side stop, the mortises may be too shallow. Check that all mortises are the exact depth of the leaf thickness — even 1/16" variation across three hinges creates noticeable alignment error.
Wood door frames, particularly in older construction with dried or deteriorated wood, may fail to hold hinge screws under the load of a heavy door. The standard repair is to remove the hinge, inject wood epoxy filler into the stripped holes, allow to fully cure, re-drill pilot holes, and reinstall the hinge with the original screws. For long-term reliability on heavy doors, use 3-inch screws that penetrate through the door stop and jamb into the structural framing behind, providing solid engagement regardless of jamb wood condition.
Steel hinges with light zinc or painted finishes will corrode when exposed to moisture, particularly on exterior doors or in high-humidity environments. Surface rust appears first at screw holes where the finish is broken, and progresses to the leaf surface and knuckle. The correct solution is replacement with stainless steel or solid brass hinges appropriate for the exposure conditions. Treating corroded steel hinges with rust-inhibiting spray is a short-term mitigation, not a permanent fix.
| vs. | Butt Hinge Comparison |
|---|---|
| Continuous (Piano) Hinges | Butt hinges concentrate load at discrete points; continuous hinges distribute load along the full door height, reducing stress on the frame. Continuous hinges are preferred for thin or lightweight door panels prone to warping. Butt hinges are standard for commercial hollow metal and heavy wood doors where load concentration at three points is structurally appropriate. |
| Pivot Hinges | Pivot hinges mount at the top and bottom of the door on the centerline, transferring load vertically to the floor rather than laterally to the frame. Pivots support heavier and wider doors than butt hinges, and allow the door to swing in both directions (if specified). Butt hinges are simpler, less expensive, and do not require floor penetration, making them the standard for conventional single-swing doors. |
| Concealed Hinges | European-style concealed hinges are invisible when the door is closed, providing a completely clean appearance. They are standard for cabinet doors but require specialized mortising and are limited in load capacity compared to commercial butt hinges. Butt hinges are the only practical choice for fire-rated commercial doors under NFPA 80 because listed concealed hinges for fire-rated applications are rare and expensive. |
| Strap Hinges | Strap hinges use long, decorative leaves that surface-mount on the face of the door rather than the edge. They are primarily used for gate, barn door, and rustic architectural applications. Butt hinges are mortised into the edge and are used for interior and commercial doors where a flush, concealed installation is required. |
Q: What is a butt hinge?
A: A butt hinge is the most common door hinge type, consisting of two rectangular leaves joined by a central knuckle and pin. Each leaf is mortised flush into the door edge and door frame, so only the knuckle is visible when the door is closed. Butt hinges are available in plain bearing, ball bearing, and spring-loaded variants, in sizes from 3.5" to 5" or larger, and in materials including steel, stainless steel, brass, and bronze. They are the standard hinge for virtually all residential and commercial door applications in North America.
Q: What size butt hinge do I need for my door?
A: Hinge size is determined by door width and weight. Use 3.5" hinges for doors up to 32" wide and 50 lbs. Use 4" hinges for doors up to 36" wide and 75 lbs. Use 4.5" (the commercial standard) for doors up to 85–100 lbs. Use 5" hinges for doors over 100 lbs or wider than 42". NFPA 80 requires a minimum 4.5" hinge for fire-rated assemblies. Always verify sizing against the door manufacturer's hardware specification sheet, which will list the recommended hinge size for the specific door model and weight.
Q: What is the difference between plain bearing and ball bearing butt hinges?
A: Plain bearing hinges use direct metal-to-metal contact in the knuckle and are adequate for light residential doors with infrequent use. Ball bearing hinges incorporate precision steel ball bearings between the knuckle sections, reducing friction dramatically, supporting heavier loads, and providing a significantly longer service life under high-cycle commercial use. ANSI/BHMA A156.1 requires ball bearing hinges for Grade 1 commercial applications. Ball bearings are also required by NFPA 80 on all fire-rated door assemblies. For any door over 50 lbs or any application with more than 50 daily cycles, ball bearing hinges are the correct specification.
Q: What is an NRP hinge and when do I need one?
A: NRP stands for Non-Removable Pin. Standard butt hinges have a removable pin that can be tapped out when the door is open, allowing the door to be lifted off its hinges even if the lock is engaged — a security vulnerability on outswing doors. NRP hinges lock the pin with a set screw or replace it with a fixed, non-extractable pin, preventing unauthorized removal. NRP hinges are required by the IBC and many security specifications on all outswing doors in commercial buildings. They are also recommended for any exterior residential outswing door where security is a concern.
Q: How many butt hinges does a door need?
A: Residential doors typically use two hinges. Commercial doors use three hinges as the standard minimum. NFPA 80 requires at least three hinges on fire-rated doors up to 90" tall and 36" wide. Doors taller than 90" require an additional hinge per 30" of height above 60". Heavy or wide doors may require four or more hinges based on weight and frame specification. Always follow the door manufacturer's required hinge schedule for the specific door model — this is particularly important for fire-rated assemblies where the hinge schedule is part of the UL listing.
Q: What butt hinge size does NFPA 80 require for fire-rated doors?
A: NFPA 80 requires a minimum 4.5" × 4.5" steel or stainless steel ball bearing butt hinge for standard fire-rated door assemblies (up to 36" wide, up to 90" tall, up to 200 lbs per pair). For heavier or wider fire doors, 5" hinges are required. All hinges must carry a UL listing for the fire-rating duration of the assembly (20-minute through 3-hour). Aluminum, brass, and bronze hinges are not permitted on fire-rated assemblies under NFPA 80 regardless of size.
Q: Can I use a butt hinge on an exterior door?
A: Yes, but material selection is critical. For exterior applications, specify stainless steel (Grade 304 or 316) or solid brass hinges. Standard zinc-plated or primed steel hinges will corrode when exposed to weather, causing staining of the door and frame, increased friction, and eventual structural failure of the hinge. In coastal and marine environments, Grade 316 stainless steel or silicon bronze is the recommended specification. Always coordinate the hinge finish with other exterior hardware (lockset, threshold, kick plate) for consistent appearance and galvanic compatibility.
UL-listed for 3-hour fire-rated assemblies — ball bearing, adjustable, Grade 1 — made in Taiwan