Angle math

Compound miter calculator for sloped staves and crown molding

Compound miters live on every sloped-side build: planters, cooperage, paint pails, lampshades, splayed-leg stools. Two angles work together — the saw miter (from the fence) and the bevel (the blade tilt) — and missing either one gives you a joint that won’t close at the corner.

The formula

miter = atan(cos(slope) × tan(180/n)) ; bevel = asin(sin(slope) × cos(180/n))

slope is how far the side leans outward from vertical: 0° is a straight box, 30° is a typical splayed planter. n is the number of sides. Both saw settings come out in degrees, applied separately on the saw — one to the fence, one to the blade tilt.

Example: 8-sided splayed planter

Eight sides leaning 15° outward from vertical. n=8, slope=15°. Miter ≈ 21.8° off the fence, bevel ≈ 5.6° blade tilt. Dead On computes both numbers, shows the saw setup in plain language, and renders the joint geometry so you can verify before re-setting the saw.

Why it matters

Compound miters are the joint most likely to fail twice: once because the math is wrong, once because the saw setup is wrong. Eyeball-and-adjust burns expensive stock. Get the two numbers on the screen, set the saw once, cut the run.

Step-by-step

  1. 1

    Pick number of sides

    Same as a regular miter — 4, 6, 8, or 12 are most common for staved work.

  2. 2

    Set the slope angle

    How far the sides lean outward from vertical. 0° is a straight box; 30° is a steep splay.

  3. 3

    Read the miter angle

    The saw fence setting — from the trigonometric formula above.

  4. 4

    Read the bevel angle

    The blade tilt setting — applied separately.

  5. 5

    Set both saw axes

    Fence to miter, blade to bevel. Dry-fit two pieces against each other to verify the corner closes flat.

Skip the math. Build the diagram.

Dead On does the compound miter calculator and 12 other woodworking calculators with visual diagrams, offline, on every Apple device signed into your Apple ID.

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Frequently asked questions

What’s the difference between a miter and a compound miter?

A standard miter is one cut angle (the saw fence). A compound miter adds a second angle (the blade tilt) so the joint can close on a sloped side, like a splayed planter or crown molding.

How do crown molding angles work?

Crown is a special case of compound miter where the slope is set by the spring angle of the molding profile (commonly 38° or 45°). Dead On includes presets for the standard spring angles.

Can I cut compound miters on a regular miter saw?

Yes, on any compound miter saw or sliding compound miter saw. The saw must allow both fence and blade tilt to be set independently.

Does Dead On show the cuts visually?

Yes. The Pro version draws the staved object and labels each cut, so you can see what the angles produce before you commit them to the saw.

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