Turn the outside size of a cabinet face frame into a cut list: two full-height stiles, rails that fit between them, and the openings that result. Add a mid stile for a pair of doors or a mid rail for a drawer above a door.
Most face frames are built with the vertical stiles running the full height of the frame and the horizontal rails fitting between them. That puts the long-grain edges of the stiles at the outside of the cabinet, hides end grain, and makes the frame easy to clamp. It also makes the arithmetic simple: stiles are the frame height, rails are the frame width minus two stile widths.
The calculator assumes rails butt between the stiles, which is how pocket-screw and dowel frames are built. For mortise-and-tenon frames, add the tenon length to each end of every rail.
stile = H · rail = W − 2 × stile width
opening W = rail − mid stile (÷ 2 if used) · opening H = H − 2 × rail width − mid rail (÷ 2 if used)
A mid stile runs between the top and bottom rails, so its length is the frame height minus two rail widths. A mid rail runs between the stiles, so it is the same length as the other rails.
Frame height 30.5 in (a common base cabinet with a 34½ in box and a 4 in toe kick under the frame), 1½ in stiles and rails, no mid stile.
| Frame width | Rails (2) | Opening W | Opening H |
|---|---|---|---|
| 12 in | 9 in | 9 in | 27.5 in |
| 15 in | 12 in | 12 in | 27.5 in |
| 18 in | 15 in | 15 in | 27.5 in |
| 21 in | 18 in | 18 in | 27.5 in |
| 24 in | 21 in | 21 in | 27.5 in |
| 30 in | 27 in | 27 in | 27.5 in |
| 36 in | 33 in | 33 in | 27.5 in |
A 24 in base cabinet. 24 × 30.5 in frame, 1½ in parts: stiles 30.5 in, rails 21 in, opening 21 × 27.5 in.
A 36 in sink base with a pair of doors. Add a 2 in mid stile. Rails are 33 in, and each opening is (33 − 2) ÷ 2 = 15.5 in wide by 27.5 in high. The mid stile itself is 30.5 − 3 = 27.5 in long.
An 18 in drawer-over-door base. Add a 1½ in mid rail. Rails (three of them) are 15 in. The two openings are each (30.5 − 3 − 1.5) ÷ 2 = 13 in high. In practice you would usually make the drawer opening shorter than the door opening — enter different numbers and use the calculator to check that the total adds up.
Mill all frame stock at once to the same thickness, and cut all parts of one length with a single stop-block setting. Mark the face and the inside edge of every part before drilling or cutting joints. Assemble on a flat surface, check diagonals for square, and let the glue cure before attaching the frame to the box.
Wider bottom rails are common when the frame sits on a toe kick or when you want a heavier look. The calculator uses one rail width for top and bottom; if yours differ, use the average and adjust the opening height by hand.
Often, yes. A wider stile where a cabinet meets a wall or another cabinet gives room to scribe or to clear door hardware.
1½ in is the common default; 1¼ in on small cabinets and 2 in or more on heavier pieces.
No. Measure the face frame itself, from the bottom of the bottom rail to the top of the top rail.
The labels say inches, but the math is unit-free. Enter everything in millimetres and read the results in millimetres.