Crown molding doesn't lie flat against the wall or ceiling — it sits at a spring angle against both, which means a single miter cut isn't enough to join two pieces cleanly at a corner. This calculator solves the two saw settings, miter and bevel, that reproduce the correct joint when the molding is cut nested flat against the saw table.
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
The spring angle — how steeply the molding's back sits against the wall — determines how much of the corner angle gets distributed between the miter and the bevel. A 38° profile and a 45° profile cut at the identical 90° corner need noticeably different saw settings (31.62°/33.86° versus 35.26°/30°), because the geometry of the tilt is different even though the wall corner hasn't changed. Always confirm which spring angle your molding uses — cutting 45° settings on 38° stock (or vice versa) produces a visibly open joint.
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.