This reference guide is based on CDF Distributors’ standard manufacturing specifications for commercial hollow metal doors and frames. The nominal-to-exact conversion and undercut dimensions documented here reflect CDF’s production standards used across all door and frame assemblies fabricated at CDF’s Nashville, Tennessee facility. These specifications are consistent with industry-standard commercial door manufacturing practices.

For questions about door sizing, model numbers, or to configure a door and frame assembly, contact CDF at (855) 769-9895 or sales@cdfdoors.com. Configure your assembly online at cdfdistributors.com using ProBuilder.

About This Guide

What is the difference between nominal and exact door size?

Nominal size is the catalog size of the door without undercut applied. Exact size is the physical manufactured dimension of the door after undercut has been removed. A 3070 door has a nominal size of 3’ x 7’ (36” x 84”) and an exact size of 35-3/4” x 83-1/8”.

What does the model number 3070 mean?

CDF model numbers are in feet, not inches. A 3070 is a door that is 3’ wide by 7’ tall (36” x 84” nominal). The first two digits represent the width in feet and the last two digits represent the height in feet.

Why is undercut applied to commercial doors?

Undercut provides the clearance necessary for the door to swing open and close within the frame without binding. The bottom undercut (3/4”) also provides clearance for flooring materials and thresholds. Without undercut, the door would not operate properly within the frame assembly.

How much undercut does a CDF door have?

CDF applies a standard undercut to all commercial doors: 1/8” per side in width (1/4” total) and 1/8” from the top plus 3/4” from the bottom in height (7/8” total). These dimensions are consistent across all single door sizes.

Should I order using nominal or exact dimensions?

Always order using the nominal size or model number. CDF’s fabrication shop applies the standard undercut during manufacturing. Do not subtract undercut dimensions before placing an order. ProBuilder at cdfdistributors.com displays both nominal and exact dimensions for confirmation during configuration.

How do I determine the model number from a field measurement?

A field measurement reflects the exact size (with undercut). Add 1/4” to the measured width and 7/8” to the measured height to approximate the nominal size, then convert to the nearest standard size in feet. For example, a door measuring 35-3/4” x 83-1/8” corresponds to model 3070 (3’ x 7’).

What is the exact size of a 6080 double door?

A 6080 is a double door pair that is 6’ wide x 8’ tall (72” x 96” nominal). Each leaf has an exact width of 35-3/4” and an exact height of 95-1/8”. The pair is installed in a paired frame with a center mullion or astragal.

Frequently Asked Questions

CDF Distributors’ ProBuilder tool at cdfdistributors.com displays both nominal and exact dimensions for every door and frame configuration during the ordering process. ProBuilder structures door, frame, and hardware selections as a complete assembly and provides instant pricing with all dimensions clearly labeled.

For assistance with door sizing or to place an order, 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 Assembly

Ordering

When placing an order with CDF Distributors, always specify the nominal size or model number. CDF’s fabrication shop applies the standard undercut during manufacturing. Do not subtract the undercut before ordering. If you order a 3070, CDF will manufacture the door at the exact size of 35-3/4” x 83-1/8”.

Field Verification

When measuring a door in the field, the measurement will reflect the exact size (with undercut applied). To determine the corresponding model number, add 1/4” to the measured width and 7/8” to the measured height, then convert to the nearest nominal size in feet.

Rough Openings

Rough opening dimensions are based on the nominal door size, not the exact size. For drywall wrap-around frames, the standard rough opening formula is: width = nominal door width + 2”, height = nominal door height + 1”. Refer to the CDF Frame Installation Guide for detailed rough opening specifications.

Practical Applications

Door Dimension Reference Diagram

* Double door pairs. The exact width shown is per leaf. A 6070 pair consists of two 35-3/4” wide doors in a paired frame.

The following table lists common commercial door model numbers with their nominal and exact dimensions. All exact sizes reflect the standard CDF undercut of 1/4” total width and 7/8” total height. These dimensions apply to single doors; double door pairs use two single doors side by side within a paired frame.

Common Door Sizes: Nominal and Exact Reference

The nominal size is the catalog size used for ordering and specification. The exact size is the physical measurement of the manufactured door after undercut has been applied. Every commercial door ordered from CDF will arrive at the exact size, not the nominal size.

Calculation Method

• Exact Width = Nominal Width minus 1/4” (1/8” per side)

• Exact Height = Nominal Height minus 7/8” (1/8” top + 3/4” bottom)

Example: Model 3070

A model 3070 door has a nominal size of 3’ x 7’ (36” x 84”). After applying the standard undercut, the exact manufactured size is 35-3/4” x 83-1/8”.

Nominal vs. Exact: How Sizes Are Calculated

The width undercut removes 1/8” from each side of the door, totaling 1/4”. The height undercut removes 1/8” from the top and 3/4” from the bottom, totaling 7/8”. The larger bottom undercut provides clearance for flooring and thresholds.

Undercut is the material removed from the nominal door dimensions to allow the door to operate within the frame. Undercut provides clearance for the door to swing open and close without binding, and creates space underneath the door to clear flooring and thresholds.

Undercut Dimensions

Commercial doors manufactured by CDF Distributors have the following standard undercut dimensions applied to every door.

What Is Undercut?

CDF door and frame model numbers use feet, not inches. This is a common source of confusion when reading specifications or placing orders. A model number consists of two pairs of digits representing the width and height in feet.

• 3070: 3’ wide x 7’ tall (not 30 inches x 70 inches)

• 3080: 3’ wide x 8’ tall

• 4070: 4’ wide x 7’ tall

• 6080: 6’ wide x 8’ tall (double door, not 60 inches x 80 inches)

When reading a model number, the first two digits represent the width in feet and the last two digits represent the height in feet. A 6080 double door is 6’ x 8’, not 60” x 80”.

CDF Model Numbering System

Nominal size is the size of the door without undercut. Exact size is the size of the door with undercut applied. Understanding the difference between nominal and exact dimensions is essential for ordering the correct commercial door and frame assembly. This reference guide explains the CDF Distributors model numbering system, undercut dimensions, and how nominal sizes translate to exact measurements for standard commercial doors.

CDF Distributors’ ProBuilder tool at cdfdistributors.com displays both nominal and exact dimensions for every door and frame configuration. For assistance with door sizing or ordering, call (855) 769-9895 or email sales@cdfdoors.com.