Cabinet Door Calculator

What this cabinet door calculator figures out

A cabinet door is almost never the same size as the hole it covers. An overlay door is bigger than the opening, because it laps onto the face frame on every edge. An inset door is smaller than the opening, because it has to swing inside it with a thin, even gap all round. Get that one detail wrong and every door on your cut list is scrap.

This calculator takes the opening you measured, the number of doors you want in it, and the gap you plan to leave, then hands back the width and height to cut for each door plus the hinge count. It works for refacing one bank of kitchen cabinets or for sizing every door in a new build. Everything runs in your browser, so your measurements never leave the page.

You need four numbers before you start. The opening width, the opening height, the overlay or reveal you want per side, and the gap between a pair of doors. All four are inches, and fractions work fine, so 1/8 inch is typed as 0.125.

Overlay or inset: the two ways a door hangs

Overlay and inset are the two families of cabinet door, and the arithmetic runs in opposite directions.

An overlay door sits on the face of the cabinet. Its edges lap over the frame, so it is bigger than the opening by the overlay amount on each side. A full overlay door leaves about 1/4 inch of frame showing between two doors, and a half overlay door leaves about 1 inch, which is the look on most older framed cabinets.

An inset door drops into the opening so the door face ends up level with the frame. It is smaller than the opening by the reveal on each side. Because the gap shows on all four edges, an inset door has to be square and the opening has to be square, which is why inset kitchens cost more.

If you are replacing doors on existing cabinets, look at the hinge first. A hinge bored into the back of the door is a European cup hinge and almost always means overlay. A hinge screwed to the frame and the door edge usually means inset.

How much gap to leave between doors and drawers

The gap you leave is the difference between doors that close cleanly and doors that bind, scrape or show an uneven line. Small gaps look sharper, but they give you less room for a door that is slightly out of square or a hinge that is a hair off.

The Architectural Woodwork Institute sets the standard uniform reveal for casework at 3.2 mm, which is 0.125 inch, with a variance of plus or minus 1.6 mm, or 0.063 inch. Its manufactured wood casework aesthetic standard also puts the horizontal reveal under a countertop edge at 3.2 mm to 9.6 mm on premium work, which is 1/8 to 3/8 inch.

Pick one gap and use it on every door in the run. A run where one gap is 1/8 inch and the next is 3/16 inch reads as sloppy even when the doors themselves are cut well.

The two formulas behind the door size

Two formulas cover every door in the kitchen. The width formula changes with the door style and the number of doors; the height formula does not care how many doors you hang.

For an overlay door:

• Door width = (opening width + 2 x overlay, minus the gap between doors) / number of doors
• Door height = opening height + 2 x overlay

For an inset door:

• Door width = (opening width, minus (number of doors + 1) x reveal) / number of doors
• Door height = opening height - 2 x reveal

Notice the difference in the width formula. An overlay pair loses one gap, the one between the two doors. An inset pair loses three reveals, the two outer edges plus the one between the doors. That is the single most common place a cut list goes wrong.

A single door in a 15 inch opening with 1/2 inch overlay is (15 + 1 - 0) / 1 = 16 inches wide and 15 + 1 = 16 inches tall. The same opening with an inset door at 1/8 inch reveal is (15 - 0.25) / 1 = 14 3/4 inches wide and 14 3/4 inches tall. One opening, two doors more than an inch apart in size.

How many hinges a cabinet door needs

Hinges are sized by door height first and door weight second. A short light door wants two, a tall pantry door wants four or five, and a wide heavy door wants one more than the height rule alone would suggest. The Builders Hardware Manufacturers Association publishes ANSI/BHMA A156.9 for cabinet hardware, and a Grade 1 hinge under that standard has to survive 100,000 open and close cycles.

There is one more rule worth knowing. The distance between the top hinge and the bottom hinge needs to be greater than the width of the door. If it is not, the door will rock on its hinges no matter how carefully you set them. That rule is why a wide, short drawer front door can need a third hinge even though it is under 40 inches tall.

Hardware makers also rate hinge count by weight bands, commonly under 15 pounds, 15 to 30, 30 to 45 and 45 to 60. A solid wood door with a raised panel is heavier than a veneered one of the same size, so when you are on a band boundary, buy the extra hinge.

Worked example: a 30 inch base cabinet with two doors

Here is the full run for a base cabinet with a 30 inch wide, 30 inch high opening, two overlay doors, 1/2 inch overlay per side and a 1/8 inch gap between the doors.

• Door width = (30 + 2 x 0.5 - 0.125) / 2 = 30.875 / 2 = 15.4375 inches, which is 15 7/16 inches
• Door height = 30 + 2 x 0.5 = 31 inches
• Doors to cut = 1 opening x 2 doors = 2 doors, or 12 doors for a run of 6 openings
• Hinges = 31 inches is under 40, so 2 per door, which is 24 hinges for 12 doors
• Door area = 15.4375 x 31 / 144 = 3.32 square feet each, or 39.88 square feet for 12 doors

Change that same opening to inset with a 1/8 inch reveal and the numbers flip. Door width = (30 - 3 x 0.125) / 2 = 29.625 / 2 = 14.8125 inches, which is 14 13/16 inches. Door height = 30 - 0.25 = 29 3/4 inches. The two doors are 5/8 inch narrower and 1 1/4 inch shorter than the overlay pair, all from changing one dropdown.

That difference matters when you order. A door 5/8 inch too wide has to be recut, and on a prefinished door that means the finish edge is gone too.

Measure twice, cut once: getting it right the first time

Cabinet doors are the one thing in a kitchen you cannot fudge into place, so the measuring is worth doing slowly. The rule is measure twice and cut once, and here is what that looks like in practice.

• Measure the opening three times. Take the width at the top, the middle and the bottom, and use the smallest of the three. Do the same for the height at the left, the middle and the right.
• Check the diagonals. Measure corner to corner both ways. If the two numbers differ by more than 1/8 inch, the opening is out of square and an inset door will never sit right.
• Write the cut list before you touch the saw. List each door with its width, its height and where it goes. Doors 1/16 inch apart are not interchangeable.
• Label the back of every door. Pencil the cabinet position on the back before you drill, not after.
• Dry fit with the hinges on. Hang one door, check the reveal on all four sides, then do the rest. A door that has to be forced is a door that was cut too big.
• Cut one test piece first. Run a scrap of the same material through the same saw setup and measure the result. Blade kerf and fence error show up there, not on the good stock.

If the opening is out of square by more than 1/8 inch, shim the cabinet before you size the doors. Sizing doors to a crooked opening just moves the problem to the door.

Wood movement, and why a door that fits today can stick later

Wood is not a stable material. It takes on and gives off moisture with the air around it, and it swells and shrinks as it does. The USDA Forest Products Laboratory covers this in Chapter 4 of the Wood Handbook, and the practical takeaway is simple: no big dimensional change happens if the wood is built and installed at a moisture content close to the average conditions it will live in.

In a house that means a gap cut in a dry February can close up in a humid August. A solid wood door 20 inches wide can move 1/16 inch or more across its width between seasons. Plywood and MDF move less, which is why most painted doors use a engineered panel inside a solid frame.

Three habits keep movement from ruining a good fit. Let the material sit in the room for a week before you cut it. Finish all six faces, including the top and bottom edges, so moisture moves in and out at the same rate. And leave the full gap on every door rather than squeezing the reveal down to nothing.

This is a planning estimate for a home project, not a shop drawing. Confirm hinge counts and load ratings against the hardware maker's own table before you buy, and follow the tool manufacturer's safety instructions when you cut.