What is the difference between jamb depth and throat size?

Jamb depth is the total width of the frame profile from face to face, including the returns that wrap over the wall surface. Throat size is the inside measurement between the returns, which equals the wall thickness. On a drywall wrap-around frame, the jamb depth is always 1 inch greater than the throat size.

How do I calculate jamb depth from wall thickness?

Add 1 inch to the wall thickness. For example, a 4-5/8” wall requires a frame with a 5-5/8” jamb depth. The extra inch accounts for the two ½-inch returns that wrap over the drywall on each side of the wall.

What is the most common jamb depth for commercial door frames?

The two most common jamb depths are 5-5/8” and 5-7/8”. A 5-5/8” jamb depth fits a 4-5/8” wall (typical 2x4 wood stud or 3-5/8” metal stud with 1/2” drywall on each side). A 5-7/8” jamb depth fits a 4-7/8” wall (the same stud types with 5/8” drywall on each side).

What happens if I order the wrong jamb depth?

A frame with the wrong jamb depth will not sit flush against both sides of the wall. If the jamb depth is too small, the returns will not reach the wall surface, leaving gaps. If the jamb depth is too large, the returns will protrude past the wall. Either condition prevents proper installation and may void fire ratings on rated assemblies. Measuring the wall thickness before ordering is the single most effective way to avoid this problem.

Does jamb depth change for fire-rated frames?

No. The jamb depth formula (wall thickness + 1 inch) is the same for both fire-rated and non-rated drywall wrap-around frames. Fire-rated frames at 20-minute, 45-minute, 60-minute, and 90-minute levels all follow the same calculation. However, assemblies requiring a 3-hour (180-minute) rating must use masonry frames, which have different depth requirements.

Can I use an adjustable frame if I am unsure of the wall thickness?

Yes. Adjustable throat frames feature a split jamb design that accommodates a range of wall thicknesses. They are useful when wall thickness is unknown at the time of ordering or varies across multiple openings. Adjustable frames are typically more expensive and may not be available in all fire-rated configurations. Contact CDF to confirm availability.

Where do I measure wall thickness for a door frame?

Measure at the rough opening where the frame will be installed. Place a tape measure across the edge of the wall from finished surface to finished surface. Take measurements at the top, middle, and bottom of the opening. Include all finish layers (drywall, plaster, tile backer board). If measurements vary, use the largest measurement.

What wall thickness does a 4-5/8 inch throat size accommodate?

A 4-5/8” throat size accommodates a 4-5/8” wall. This is one of the most common wall thicknesses in commercial construction, corresponding to a 2x4 wood stud with 1/2” drywall on each side, or a 3-5/8” metal stud with 1/2” drywall on each side. The corresponding jamb depth for this throat size is 5-5/8”.

Frequently Asked Questions

CDF’s ProBuilder tool allows contractors, architects, and facility managers to configure drywall frame assemblies online at cdfdistributors.com. During configuration, ProBuilder prompts for wall thickness and automatically calculates the correct jamb depth and throat size. ProBuilder displays compatible options and provides instant pricing for complete door and frame assemblies.

For assistance with your order or to verify jamb depth for your wall condition, call (855) 769-9895 or email sales@cdfdoors.com. CDF’s sales team is available Monday through Friday, 7:30 AM to 4:30 PM CT.

Configure Your Frame Assembly

In situations where the exact wall thickness is unknown at the time of ordering, or where wall thickness varies across multiple openings in a project, adjustable throat frames provide flexibility. These frames feature a split jamb design that can be expanded or compressed to accommodate a range of wall thicknesses.

Adjustable frames are available for common wall thickness ranges and eliminate the risk of ordering a frame with the wrong fixed jamb depth. However, they are typically more expensive than standard fixed-throat frames and may not be available in all fire-rated configurations. Consult CDF for availability and rating options.

Adjustable Throat Frames

The jamb depth formula described in this guide (wall thickness + 1 inch) applies specifically to drywall wrap-around frames, which are the most common frame type for commercial interior applications. Other frame types use different installation methods and may calculate jamb depth differently.

Drywall Wrap-Around Frames vs. Other Frame Types

Fire-rated door assemblies are available at 20-minute, 45-minute, 60-minute, 90-minute, and 3-hour (180-minute) rating levels. The jamb depth formula (wall thickness + 1 inch) applies equally to fire-rated and non-rated drywall wrap-around frames. However, fire-rated installations carry additional requirements that make correct jamb depth selection even more critical.

• Drywall wrap-around frames can achieve fire ratings up to 90 minutes. For assemblies requiring a 3-hour (180-minute) rating, masonry frames must be used instead of drywall wrap-around frames.

• All components in a fire-rated assembly (door, frame, hinges, lockset, closer, glass, and louvers) must carry matching fire labels.

• The frame must fit the wall tightly with no gaps. An incorrect jamb depth that results in gaps between the frame and wall can cause the assembly to fail inspection.

CDF rivets fire labels onto every fire-rated frame before shipping. Verify all code requirements with project specifications and the AHJ.

Jamb Depth for Fire-Rated Frames

Selecting the correct jamb depth is critical for proper frame installation and long-term performance. A mismatch between the frame depth and wall thickness creates problems that cannot be easily corrected after the frame is installed.

• Frame too narrow (jamb depth too small). The frame returns will not reach the wall surface. This leaves a visible gap between the frame face and the drywall, prevents the compression anchors from seating properly, and compromises the structural integrity of the installation.

• Frame too wide (jamb depth too large). The frame returns will extend past the wall surface and protrude into the room. This creates an uneven appearance, interferes with trim or casing, and may prevent the door from closing properly against the frame stop.

• Incorrect jamb depth on fire-rated assemblies. On fire-rated frames (20-minute, 45-minute, 60-minute, 90-minute, and 3-hour ratings), an improper fit can void the fire rating. Fire-rated assemblies require the frame to sit tightly against the wall with no gaps that could allow flame or smoke passage. The Authority Having Jurisdiction (AHJ) may reject an installation where the frame depth does not match the wall condition.

Why the Correct Jamb Depth Matters

The table below lists the most common wall constructions encountered in commercial and residential projects, along with the corresponding throat size and jamb depth for a standard drywall wrap-around frame. Use this table as a quick reference when ordering frames or verifying specifications.

Common Wall Thicknesses and Corresponding Frame Dimensions

Accurate wall thickness measurement is the starting point for selecting the correct frame. The wall thickness determines both the throat size and the jamb depth. The following method applies to finished drywall walls where the frame will be installed as a wrap-around.

• Measure at the door opening. Place a tape measure across the edge of the wall at the rough opening, from the finished surface on one side to the finished surface on the other side. This measurement is the wall thickness and equals the throat size.

• Measure in multiple locations. Take measurements at the top, middle, and bottom of the opening. Walls can vary in thickness due to uneven stud placement or drywall buildup.

• Include all finish layers. The measurement must include drywall, plaster, tile backer board, or any other finish material applied to the wall surface. The frame wraps around the entire finished wall assembly.

If measurements vary by more than 1/8” across the opening, use the largest measurement to ensure the frame throat is not too narrow for the wall. A frame that is slightly wider than the wall can be shimmed; a frame that is too narrow will not seat properly.

How to Measure Wall Thickness

The relationship between jamb depth and throat size follows a simple formula that applies to all standard drywall wrap-around frames. Understanding this formula allows you to convert between the two measurements and verify that a frame matches your wall condition.

• Jamb Depth = Wall Thickness + 1 inch

• Throat Size = Wall Thickness (they are the same measurement)

• Jamb Depth = Throat Size + 1 inch

For example, if your wall thickness is 4-5/8”, the throat size is 4-5/8” and the required jamb depth is 5-5/8”. The extra 1 inch accounts for the two ½-inch returns that wrap over the face of the drywall on each side of the wall.

The Jamb Depth Formula

Throat size is the inside measurement of the door frame, taken between the two inner edges of the frame returns. The throat size corresponds directly to the wall thickness the frame is designed to fit around. A frame with a 4-5/8” throat is designed for a 4-5/8” wall. A frame with a 4-7/8” throat is designed for a 4-7/8” wall.

Throat size is the dimension most commonly specified on architectural drawings and door schedules because it communicates the wall condition directly. When a specification calls for a particular throat size, it is telling the frame manufacturer what wall thickness the frame must accommodate.

What Is Throat Size?

Jamb depth is the overall width of the door frame profile, measured across the full cross-section from one face to the other. It includes the throat (the portion that wraps around the wall) plus the two returns that extend past the wall surface on each side. On a standard drywall wrap-around frame, each return adds ½ inch, so the jamb depth equals the wall thickness plus 1 inch.

Jamb depth is sometimes referred to as frame depth or overall frame width. Regardless of the term used, it always describes the same measurement: the total distance across the frame profile from face to face.

What Is Jamb Depth?

This reference guide is published by CDF Distributors, a commercial door and frame manufacturer and distributor headquartered in Nashville, Tennessee. CDF fabricates hollow metal frames in-house and ships complete door and frame assembly nationwide. The technical content in this guide reflects CDF’s standard fabrication specifications and the terminology used across the commercial door industry. CDF’s engineering and sales teams field thousands of jamb depth and throat size questions annually from contractors, architects, and facility managers ordering drywall wrap-around frames.

About This Guide

Jamb depth is the total width of a door frame’s cross-section, measured from the face of the frame on one side of the wall to the face on the opposite side. Throat size is the inside measurement between the two returns of the frame, which equals the wall thickness the frame is designed to wrap around. On a drywall wrap-around frame, the jamb depth is always 1 inch greater than the throat size because each side of the frame extends ½ inch beyond the wall surface to create the wrap. Selecting the correct jamb depth ensures the frame sits flush against both sides of the finished wall with no gaps or overhangs.

CDF Distributors’ ProBuilder tool at cdfdistributors.com automatically calculates the correct jamb depth based on the wall thickness you enter during configuration. For assistance determining your jamb depth or throat size, call (855) 769-9895 or email sales@cdfdoors.com.