These settings are for crown molding laid flat on the saw table. Nested upright cutting is a different setup. Use the included wall angle: miter = atan(sin(spring)×tan((180−corner)/2)); bevel = asin(cos(spring)×sin((180−corner)/2)). At 120°/38°, the settings are 19.57° and 23.20°.
Why crown molding needs two angles, not one
Flat trim like baseboard or door casing lies in a single plane, so joining two pieces at a corner only needs one saw rotation — the miter angle. Crown molding is different: it spans the angle between the wall and ceiling, so it's tilted relative to both surfaces at once. Cutting it correctly at a corner requires rotating the saw (the miter angle) and tilting the blade (the bevel angle) simultaneously — a compound cut. Skip the bevel and the joint gapes open even if the miter angle looks right on paper.
Why the spring angle changes the numbers
These settings are for crown molding laid flat on the saw table. Nested upright cutting is a different setup. Use the included wall angle: miter = atan(sin(spring)×tan((180−corner)/2)); bevel = asin(cos(spring)×sin((180−corner)/2)). At 120°/38°, the settings are 19.57° and 23.20°.
Cutting flat (nested) versus cutting upright
This calculator's formula assumes the standard shop method: the molding lies flat against the saw table, tilted at its spring angle exactly as it will sit against the wall and ceiling once installed, and the saw does both the rotation and the tilt. Some carpenters instead cut crown molding standing upright against a fence using only a single miter angle and a specialty jig — a different technique with different math that this tool does not model. Confirm which method your setup uses before applying these numbers.
Limits and edge cases
This calculator handles the standard two-surface (wall-and-ceiling) compound miter for crown molding and similarly spring-angled trim. It assumes a perfectly straight, symmetric corner and molding profile — hand-shaped or out-of-plane moldings may need a test cut to confirm the fit. For simple single-plane trim with no spring angle (baseboard, flat casing), use the standalone Trim Miter Angle Calculator instead, which only needs the corner angle.