Compound Miter Calculator

Calculate saw miter and bevel settings for crown molding laid flat, or ordinary miter settings for flat trim and baseboard.

Structural 5 inputs 8 results

Inputs

View results

Trim mode

Joint type

Corner angle (C)

Crown spring angle (S)

Molding face width (W)

Results

Default result

Edit inputs

Saw miter setting(M)

31.62°

Pass

crown on flat

Also computed

Saw bevel setting(B)33.86°

tilt saw blade

Flat trim miter(M_flat)45°

Approx wall/drop projection(W_wall)2.758in

Approx ceiling projection(W_ceil)2.155in

Spring angle used(S)38°

Spring complement(90-S)52°

Method notes 4 notes

Crown mode assumes the crown is cut lying flat on the saw table, with spring angle measured from the wall.
Formula: miter = atan(sin(S) / tan(C/2)); bevel = asin(cos(S) x cos(C/2)).
Angles are magnitudes for a inside corner. Left/right and face-up/face-down orientation varies by saw, blade tilt and which piece you are cutting.
Real crown profiles, out-of-plumb walls, scarf joints and coping strategy can require shop adjustment after the calculated setting.

Compound miter cuts for crown molding need both saw rotation and blade bevel. This calculator uses the crown-on-flat relations miter = atan(sin(S) / tan(C/2)) and bevel = asin(cos(S) x cos(C/2)), where C is the measured corner angle and S is the crown spring angle from the wall. Flat trim mode reduces the workflow to ordinary baseboard or casing miter cuts with zero bevel.

How to use this calculator

Choose trim mode. Use crown molding laid flat for compound cuts, or flat trim/baseboard for ordinary miter cuts.
Measure the corner. Enter the included angle between the two finished walls or trim runs.
Enter spring angle. For crown, enter the installed angle from the wall to the crown profile.
Set the saw and test. Use the miter and bevel magnitudes, then verify left/right orientation on scrap before cutting finished trim.

How it works

For crown molding cut flat on the saw, the calculator treats the installed crown as a tilted plane. With corner angle C and spring angle S, the saw settings are:

miter = atan(sin(S) / tan(C / 2))

bevel = asin(cos(S) x cos(C / 2))

For flat trim or baseboard, the bevel is zero and the miter setting is:

miter = (180 - C) / 2

Worked example

Verified against the live calculator

For a square 90 deg inside corner with 38 deg crown spring angle, the calculator returns a saw miter setting of about 31.62 deg and a bevel setting of about 33.86 deg. Flat trim on the same corner would use a 45 deg miter and 0 deg bevel.

Frequently asked questions

What is a compound miter cut?

A compound miter cut uses both the saw miter rotation and the blade bevel tilt. Crown molding laid flat usually needs both settings.

What spring angle should I enter for crown molding?

Use the installed angle from the wall to the crown profile. Common 38/52 crown uses 38 degrees in this calculator, but measure or check the molding specification.

Are inside and outside corner settings different?

The angle magnitudes are the same. The board face, left/right piece, blade tilt direction and keeper side change, so always test the orientation on scrap.

Can I use this for baseboard or casing?

Yes. Choose flat trim/baseboard mode. The calculator then uses the ordinary flat miter relation and returns zero bevel.

Method & assumptions

Corner angle is the included angle between the two finished walls or trim runs.
Crown spring angle is measured from the wall to the installed crown profile.
Results are angle magnitudes. Saw orientation, board side, blade tilt direction and keeper side depend on the exact saw setup.
Out-of-plumb walls, bowed trim, coped joints, scarf joints and complex crown profiles can require adjustment from the calculated value.
For the exact miter search path, use the miter angle calculator.
For material planning, pair this with the board feet calculator or wood movement calculator.

Compound Miter Calculator

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