Miter Saw Angle Calculator
Find the exact miter and bevel angles to set on your miter saw for polygon frames, inside corners, and crown molding compound cuts. Use it any time you need precise angle settings beyond a basic 45°.
About this calculator
For a regular polygon frame, each corner's miter angle equals 90° divided by the number of sides for inside cuts, or twice that for outside cuts: miterAngle = (90 / numberOfSides) × (projectType === 'inside' ? 1 : 2). When cutting crown molding, the spring angle (the angle at which the molding sits against the wall) introduces a bevel component. The bevel correction is calculated using: bevelCorrection = arcsin(sin(springAngle) × sin(materialThickness)) × (180 / π). These two values are added together to give the full compound cut angle. A 4-sided frame uses 45° miters; a 6-sided hexagon frame uses 30° miters. Crown molding with a 38° spring angle requires a non-zero bevel adjustment that prevents gaps at the ceiling line. Always test on scrap material before cutting your final workpiece.
How to use
Example: cutting an octagon (8-sided) picture frame with outside corners, no crown molding. Step 1 — Enter numberOfSides = 8, projectType = 'outside', springAngle = 0. Step 2 — Miter angle = (90 / 8) × 2 = 11.25 × 2 = 22.5°. Step 3 — Since springAngle = 0, the bevel correction = 0. Step 4 — Set your miter saw to 22.5° and bevel to 0°. Each of the 8 pieces gets identical 22.5° miters on both ends, and they assemble into a perfect regular octagon. For a 6-sided hexagon outside frame: (90 / 6) × 2 = 30°.
Frequently asked questions
What miter angle do I need for a hexagon picture frame?
A regular hexagon has 6 sides, so each corner is 60°. For an outside-corner frame, the miter angle on each end of each piece is (90 / 6) × 2 = 30°. You would set your miter saw to 30° and cut both ends of all six pieces identically. When assembled, the six 60° corners will total 360°, forming a closed hexagon. Always cut a test piece first to confirm your saw's detent is accurate at 30°.
How do I calculate crown molding miter and bevel angles for a corner?
Crown molding sits at a spring angle relative to the wall, which means a simple flat miter will not produce a tight fit — you need a compound cut combining a miter angle and a bevel angle. This calculator uses the spring angle and material thickness to compute the bevel correction via arcsin(sin(springAngle) × sin(materialThickness)). Common spring angles are 38° and 45°; check the back of your molding or the manufacturer's spec. Many woodworkers also use the flat-on-the-table method to avoid bevel settings entirely.
Why do inside and outside polygon corners require different miter angles?
An inside corner adds up to a total angle less than 180°, while an outside corner exceeds 180°. For a square box, inside corners each measure 90° and each miter is 45°, whereas outside corners on a picture frame also happen to be 45° — but for other polygon counts, the inside vs. outside distinction produces different miter settings. The formula scales by a factor of 1 for inside cuts and 2 for outside cuts, reflecting that outside miters must account for the full exterior angle of the polygon.