Compound Angle Calculator — Mitre & Bevel Settings

A compound angle combines both a mitre (rotation in the horizontal plane) and a bevel (tilt of the blade). It is needed when pieces meet at a corner that is not perpendicular, such as the sides of a planter box with sloped walls or a hopper.

Compound angles are needed when building anything with sloped sides that also have mitre joints at the corners. Common examples: tapered planters, crown moulding, pyramid forms, sloped-sided boxes, and picture frames with bevelled edges.

Set the mitre angle by rotating the turntable — most saws read 0 at a 90° cross-cut, so you dial the mitre angle itself. Set the bevel angle by tilting the blade to that angle from vertical. Many mitre saws have limited bevel capacity, so check your saw can achieve the required tilt before starting.

For a 4-sided box (square) with walls sloping inward at 10 degrees from vertical: the mitre (turntable) angle is about 9.9 degrees and the bevel (blade tilt) is about 44.1 degrees. These come from mitre = arctan(sin(10) x tan(45)) = 9.85° and bevel = arcsin(cos(10) x sin(45)) = 44.14°. Use this calculator to get exact values for your specific combination.