What is a compound angle?

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.

When do I need compound angles?

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.

How do I set compound angles on my mitre saw?

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.

What compound angles do I need for a 4-sided planter with 10 degree slope?

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.

WoodCalcs

Compound Angle Calculator — Mitre & Bevel Settings

Calculate compound mitre and bevel angles for angled joinery and sloped assemblies.

Number of Sides

4 = square, 6 = hexagon, 8 = octagon

Slope Angle from Vertical

0° = vertical, 90° = horizontal

How We Calculate This

This calculator determines the mitre and bevel settings for a compound angle joint on a regular polygon with sloped sides.

Formulas

Mitre angle = arctan(sin(slope) x tan(180/n))

Bevel angle = arcsin(cos(slope) x sin(180/n))

Where n = number of sides and slope = angle of the side from vertical. The bevel angle is the saw blade-tilt setting directly — set the blade to this tilt from vertical. There is no separate "90 minus bevel" step.

Most mitre saws read 0 at a 90° cross-cut, so you dial the mitre angle itself on the turntable. The cross-cut figure (90 minus mitre) only applies to saws or protractors that reference the fence — check your saw's scale before cutting.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify measurements and material quantities before cutting or purchasing.