How do you measure an undercut door?

Author: Nat Spinka  |  Last update: Saturday, May 23, 2026

The term undercut refers to the dimension measured from the bottom of the door frame to the bottom of the door. Most commercial doors are designed with a 3/4-in. undercut, but other dimensions (smaller and larger) are common.

How do you calculate door undercut?

The formula in which to determine Undercut is derived by adding the total sum of the follow- ing (Floor Clearance + Floor Covering Thick- ness + Threshold Height (assuming the thresh- old is mounted on top of the floor covering) + Jamb Extensions Height.

How do you measure an undercut?

Conventional tools used to measure undercuts are profile measurement systems. A profile measurement system measures and records the profile of a target by tracing its surface with a stylus.

What size are door undercuts?

Undercut is a term used to describe the dimen- sion from the bottom of the door to the bottom of the frame. Doors are undercut to provide clearance above the finish floor material. Typically they are undercut ⅝ inches to ¾ inches from the bottom of the frame.

What is the code for door undercut?

The doors shall be close fitting within operational tolerances, and shall not have a center mullion or undercuts in excess of 3/4 inch (19.1 mm), louvers or grilles. The doors shall have head and jamb stops, and astragals or rabbets at meeting edges.

How To: Measure Your Interior Door

What is the best number for an undercut?

Number 1 (⅛ inch or 3.2 mm): Leaves a very short length, ideal for a close buzz cut or fade. Number 2 (¼ inch or 6.4 mm): Slightly longer than number 1, still in the buzz cut category but with a fuller look. Number 3 (⅜ inch or 9.5 mm): Provides a short but manageable length, suitable for a crew cut.

What is the purpose of door undercut?

By allowing air to flow freely under the door, you create a pathway for the moist air to escape and fresh air to enter. This circulation helps maintain a balanced humidity level and reduces the chances of condensation forming on surfaces.

How to measure door undercut?

The term undercut refers to the dimension measured from the bottom of the door frame to the bottom of the door.

What is the gap under a door code?

NFPA 80 (the code standard for fire doors) states that fire doors must be inspected on an annual basis. Maximum allowable perimeter gap is 1/8" for wood doors, 1/8" +/- 1/16" for metal doors. Maximum allowable door bottom gap is 3/4".

How much to undercut a door for return air?

In most applications, the door undercut would need to be 1.5 inches or greater to allow enough air to pass. There are some through-the-door alternatives that can be effective.

What is the rule of undercut?

A rule of thumb is that the undercut should be at least 1.5 threads long and the diameter should be at least 0.015 in (0.38 mm) smaller than the minor diameter of the thread. Strictly speaking the relief simply needs to be equal or slightly smaller than the minor diameter of the thread.

What is the undercut method?

Undercut machining refers to the process where material is removed from beneath the top layer or surface of a workpiece. This is often done to create a recess or groove that allows for the assembly of parts or to enhance the geometrical intricacies of a component.

How do you identify undercuts?

An occlusal view of the cast allows a clear visual- ization of the convergence of single or multiple prepared teeth (Figs. 1, E, and 2). Undercuts or excessive convergence angles can be detected when the relative position of the 2 drawn lines are observed (Fig. 3).

What is the standard undercut on a hollow metal door?

Undercut: Refers to the clearance between the bottom of the hollow metal door frame and the hollow metal door. Most hollow metal doors have a 1/8" undercut.

What is the standard gap under a door?

In general, the gap beneath an interior door will be between three-quarters of an inch and half an inch. This width depends largely on the type of flooring, as door frames are generally installed when the floor is unfinished. A standard door can have varying levels of clearance over different flooring types.

What is the minimum undercut for a door?

As a guide the average undercut of your door should be between 8mm and 10mm, that's around ⅝ inch to ¾ inch from the bottom of the frame. if you are in doubt, shave or cut off a little and if it's not enough, shave off some more. Remember less is better or you may damage the door's structural integrity.

What is the gap under the door threshold?

One common cause of gaps around door thresholds is settlement. Over time, buildings can shift and settle, causing misalignment between the door and the floor. Another cause could be improper door threshold installation, where gaps are left unintentionally.

What is the gap between a door and a floor called?

Threshold (architecture) - Wikipedia.

How much gap under internal door?

the gap between the underside of the door and unfinished floor should be between 10mm and 22mm, with the ventilation requirements for the building taken into account when determining the gap beneath internal doors.

How much space should I leave between the door and frame?

Hinge Margin: Space between the door panel and door frame on the hinge side of the door. A standard hinge margin is 1/16", but can vary based upon the hinges used. Strike Margin: Space between the door panel and door frame on the strike, or handle, side of the door. The standard strike margin is 5/32".

What is the maximum gap allowed under a fire door?

The maximum gap between the bottom of a fire door and the floor should not exceed 10mm or be less than 8mm [as set out in Building Regulation Approved Document F], except in instances where smoke protection is required by Building Regulations in which case the gap underneath the fire door should not exceed 3mm.

Why is undercut important?

The undercut is a hairstyle that leaves length on top but has the back and sides of the head closely cut or buzzed. Having an undercut emphasizes hair volume and shows off your facial structure. Whether your hair is straight, wavy, or permed, there is an undercut style that will make you look fresh and stand out.

What is the difference between undercut and overhang?

When the dot product of the two directions is larger than zero, it corresponds to undercut. The angle between the two directions forms the overhang angle at the boundary point.

What is the trim at the bottom of a door called?

Sill. Sills are the bottom component of a door frame. They are the part of the door that gets sealed and fastened to the floor.

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