Quick answer
A single door is opening width + 2 × overlay wide and opening height + 2 × overlay tall. An 18 × 30 inch opening with a ½ inch overlay needs a 19 × 31 inch door. Pairs subtract the gap and divide by two.
Enter the opening, overlay, gap and number of doors. The calculator returns the door size. Use this cabinet door size calculator to check your own figures.
Related tools: Board and Batten Layout Calculator: Number of boards and the real gap for an even board-and-batten or panel layout. Trim and Moulding Calculator: Linear feet of baseboard or trim for a room. Door Rough Opening Calculator: Framing opening size for a door from its slab size.
How to use the Cabinet Door Size Calculator
- Enter opening width (in) (above 0).
- Enter opening height (in) (above 0).
- Enter overlay on each side (in) (0 or more).
- Enter gap between a pair of doors (in) (0 or more).
- Enter doors across the opening (a whole number, between 1 and 2). It starts at 1.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Opening width | A number, in in | > 0 |
| Opening height | A number, in in | > 0 |
| Overlay on each side | A number, in in | ≥ 0 |
| Gap between a pair of doors | A number, in in | ≥ 0 |
| Doors across the opening | A whole number | ≥ 1, ≤ 2, starts at 1 |
Formula and method
Formula
single door width = opening + 2 × overlay; pair: (opening + 2 × overlay − gap) ÷ 2; height = opening + 2 × overlay
IEEE-754 double precision; shown to the decimals indicated.
Assumes the same overlay on every edge. Plan geometry only; confirm quantities with your supplier and local code before ordering.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Opening width = 18; Opening height = 30; Overlay on each side = 0.5; Gap between a pair of doors = 0.125; Doors across the opening = 1.
| Result | Value |
|---|---|
| Door size | 19 × 31 in |
| Doors | 1 |
Example 2
Inputs: Opening width = 30; Opening height = 30; Overlay on each side = 0.5; Gap between a pair of doors = 0.125; Doors across the opening = 2.
| Result | Value |
|---|---|
| Door size | 15.438 × 31 in |
| Doors | 2 |
Example 3
Inputs: Opening width = 24; Opening height = 36; Overlay on each side = 0.375; Gap between a pair of doors = 0.125; Doors across the opening = 2.
| Result | Value |
|---|---|
| Door size | 12.313 × 36.75 in |
| Doors | 2 |
The first line is the headline result (door size). Below it the cabinet Door Size Calculator lists doors, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Overlay
The overlay is how far the door overlaps the opening on each side. With ½ inch overlay on both sides the door is 1 inch bigger in each direction. For a pair the doors meet with a small gap, such as 1/8 inch.
Measure carefully
Measure the opening after the face frame is fitted and check hinge type, because full-overlay and inset hinges need different overlays. Round to the nearest practical size when ordering.
How the result changes with opening width
Holding every other input at the first worked example, this table changes only opening width. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Opening width | Door size | Doors |
|---|---|---|
| 9 | 10 × 31 in | 1 |
| 18 | 19 × 31 in | 1 |
| 36 | 37 × 31 in | 1 |
| 72 | 73 × 31 in | 1 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Opening width: entering "0" shows "Opening width must be greater than 0." beside that field and no result.
- Doors across the opening: entering "3" shows "Doors across the opening must be at most 2." beside that field and no result.
Choosing between the Cabinet Door Size Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Board and Batten Layout Calculator](/construction/board-and-batten-layout-calculator/) | wall width, board or panel width and target gap between boards | Number of boards |
| [Trim and Moulding Calculator](/construction/trim-moulding-calculator/) | room length, room width and piece length | Trim needed |
| [Door Rough Opening Calculator](/construction/door-rough-opening-calculator/) | door width and door height | Rough opening |
| [Sample Size Calculator](/statistics/sample-size-calculator/) | estimate a, confidence level and margin of error | Required sample size |
| [Portion Size Calculator](/cooking/portion-size-calculator/) | total amount of food and people | Per person |
Background: construction estimates
Material quantities are geometry plus a margin. Calculate the exact volume or area, add an allowance for waste, spillage, cuts and uneven ground (calculator pages commonly mention 5 to 10 percent, a rule of thumb that varies by material and job) and round up to whole units. One cubic yard is exactly 27 cubic feet.
Suppliers often have minimum order sizes and may charge for small loads, so confirm quantities, product yields and local code with your supplier or a qualified estimator before ordering.
Assumptions and limitations
- Measure the opening after the face frame is fitted
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for opening width and doors across the opening to confirm this.
Frequently asked questions
What is inset?
A door that sits inside the opening, flush with the frame.
How big is a pair?
(opening + 2 × overlay − gap) ÷ 2 each.
Does the hinge type matter?
Yes, it sets the overlay.
What does the Cabinet Door Size Calculator calculate?
Door size for an opening with an overlay. It returns Door size and Doors.
What formula does the Cabinet Door Size Calculator use?
single door width = opening + 2 × overlay; pair: (opening + 2 × overlay − gap) ÷ 2; height = opening + 2 × overlay. Assumes the same overlay on every edge.
What do I need to enter in the cabinet Door Size Calculator?
You enter Opening width (in), Opening height (in), Overlay on each side (in), Gap between a pair of doors (in) and Doors across the opening.
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Measure the opening after the face frame is fitted.
What is an example of a cabinet Door Size result?
With opening width 18, opening height 30, overlay on each side 0.5, gap between a pair of doors 0.125 and doors across the opening 1, the door size is 19 × 31 in.
Can I rely on this calculator for a decision?
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work. For this calculator in particular: Measure the opening after the face frame is fitted.
Related calculators
- Board and Batten Layout Calculator — Number of boards and the real gap for an even board-and-batten or panel layout.
- Trim and Moulding Calculator — Linear feet of baseboard or trim for a room.
- Door Rough Opening Calculator — Framing opening size for a door from its slab size.
- Sample Size Calculator — Sample size for estimating a mean or a proportion.
- Portion Size Calculator — Amount of food per person.
- Roof Pitch Calculator — Roof pitch as rise per 12 inches, angle, slope percent and rafter length factor.
- Clapboard Siding Calculator — Number of clapboard pieces from exposure and wall size.
- Construction Waste Calculator — Material to order after a waste allowance.
- Taper Calculator — Taper ratio and angle from large diameter, small diameter and length.
Sources
- OpenStax, Prealgebra 2e (Rice University): perimeter, area, volume, circumference and the Pythagorean theorem
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI), Appendix B conversion factors (international foot 0.3048 m, inch 25.4 mm, US gallon 3.785411784 L)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.