Woodworking calculator
Crown Molding Angle Calculator
Cutting crown molding is tricky because the trim sits at an angle to both the wall and the ceiling, so a simple miter is not enough. This calculator gives the two saw settings, the miter angle and the bevel angle, needed to cut crown lying flat on the saw table. Enter the spring angle of the molding and the corner angle of the wall, and you get the exact compound cut for clean, gap free inside and outside corners every time.
For cutting crown molding lying flat on the saw table. A 90° corner is a standard inside corner; use the actual measured angle for out-of-square walls.
How it works
Crown molding spans the joint between wall and ceiling, tilted out by its spring angle, the angle between the back of the molding and the wall, commonly 38, 45, or 52 degrees. When you lay the molding flat on the saw table instead of propping it against the fence, a single bevel cut will not match the corner. You need a compound cut: the blade swung sideways to a miter angle and tilted to a bevel angle at the same time.
The geometry reduces to two formulas. The miter angle is the arctangent of the sine of the spring angle times the tangent of half the corner angle. The bevel angle is the arcsine of the cosine of the spring angle times the cosine of half the corner angle. For a standard 90 degree inside corner with 45 degree spring molding, this gives a miter of 35.3 degrees and a bevel of 30 degrees, the familiar setting many trim carpenters memorize.
Set the corner angle to 90 for a normal square inside or outside corner, or measure the real angle with a protractor for out of square walls, which are common in older homes. Cut a scrap test piece first and adjust slightly, since small wall errors accumulate across a long run.
Worked example
A 45/45 crown in a square (90°) inside corner: miter 35.3°, bevel 30.0°, cut flat on the table.
Frequently asked questions
What is the spring angle of crown molding?
The spring angle is the angle between the flat back of the molding and the wall when it is installed. It is commonly 38, 45, or 52 degrees and is set by the molding profile, so check the manufacturer spec before cutting.
What miter and bevel do I use for 45 degree crown?
For 45 degree spring molding on a standard 90 degree corner, set the saw to a 35.3 degree miter and a 30 degree bevel. Cut the molding lying flat on the table, and verify the fit on a scrap before the real piece.
Why cut crown flat instead of against the fence?
Cutting flat on the table works for any saw and lets you handle wide molding that will not fit nested against the fence. The trade off is you must use a compound miter and bevel rather than a single angled cut.
Do these angles work for out of square walls?
Yes. Measure the actual corner angle with a protractor and enter it instead of 90 degrees, and the formulas adjust both the miter and bevel. Older houses often have corners several degrees off square, so always measure.
What is the difference between an inside and outside corner?
Inside corners meet in a concave joint, like where two walls form a room corner, and outside corners are convex, like the edge of a bumped out wall. The saw angles are the same magnitude, but the pieces are mirrored and cut on opposite sides.
Related calculators
Sources
These calculators are for planning and estimation. Engineering results (shelf sag, wood movement) use published average material properties; real boards vary by grade, grain, moisture and defects. Verify load-bearing designs with a professional.