Angled Cabinet Mitre Calculator

1. Measure the cabinet. The calculator opens on Sloped top: enter the inside width and the inside height at each end, and it works out the angles for you. If you have measured the corner angles with an angle finder or sliding bevel, switch to I've measured the corner angles.
2. Enter the board thickness. 18 mm for most MFC and MDF carcasses.
3. Choose how the joint goes together. Tap the picture for each corner: the top can sit over the side, sit under it (between the sides), or be mitred. You can set the left and right corners differently.
4. Set your saw. The bevel is the tilt of your table saw blade or track saw, measured from square (0°). The diagram shows which face has the long point.

The maths

For a mitre, each piece is cut at half the joint angle, so the saw tilt is 90° − angle ÷ 2. A 90° corner needs 45° on both pieces, a 120° corner needs 30°. For an overlapping or butt joint, only one edge is bevelled and the tilt is the difference between the joint angle and 90°. The extra length taken up by the bevel is thickness × tan(tilt), which the calculator adds to the inside sizes to give you the long point.

Which way round?

A corner over 90° (an obtuse corner, like the top of a cabinet under a shallow slope) opens out, so the long point of a mitre is on the outside face. A corner under 90° closes in. Always cut a test piece from an offcut first and offer it up.