How this miter angle calculator works
For a corner angle C and a spring angle S, laid flat on the saw table (the standard modern method, as opposed to holding crown upside-down against the fence):
miter = atan( tan(C / 2) × sin(S) )
bevel = asin( cos(C / 2) × cos(S) )
Flat trim is the special case S = 90°, where sin(S) = 1 and cos(S) = 0 — the formula collapses to miter = C / 2 and bevel = 0, which is exactly the simple miter rule for baseboard, casing, and picture frames.
Sources
Formula and worked reference check (90° corner, 38° spring → 31.62° miter, 33.86° bevel, the standard 38/52 crown setting) from Starlight Tools' compound miter crown molding calculator and "Compound Miter Cuts for Crown Molding: The Angle Math That Actually Works". Verified against this calculator on September 18, 2026.
Questions
What is a compound miter cut?
A cut that combines a miter angle (table rotation) with a bevel angle (blade tilt), needed whenever molding sits at a spring angle against the wall and ceiling instead of lying flat. Crown molding is the common example.
What is spring angle?
The angle the back of the molding makes with the wall when installed. The two common crown profiles are 38° spring (labeled 52/38) and 45° spring (labeled 45/45); flat trim like baseboard or a picture frame has no spring angle, so its bevel is always 0°.
Why is the miter angle for crown molding not just half the corner angle?
Because the molding is tilted against the wall at the spring angle, the saw doesn't see the room's true corner angle — it sees that angle projected through the spring tilt. Trigonometry corrects for it, which is why 38° crown and 45° crown need different saw settings for the same 90° corner.
How do I find the actual corner angle?
Measure it with a digital angle finder or draw the two walls and measure with a protractor — don't assume 90°. Many room corners are a degree or two off, and crown molding is unforgiving of that error.
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