Compound Miter Calculator
Live resultInside Corner
ActiveCrown lies flat on its back on the table, decorative face up, with the ceiling edge against the fence. This cut: left piece. Swing the miter and tilt the bevel to the results above.
Outside Corner
Crown miter & bevel reference
Two numbers come off the saw at every crown corner, and both of them move when the spring angle or the wall corner moves. The tables below hold the values a finish carpenter reaches for most: the three stock spring angles, precomputed miter and bevel settings across the corner angles a real wall actually reads, the closed-form math behind them, and the stock lengths and saw-orientation rules that decide whether a cut becomes trim or scrap.
Stock spring angles
Crown molding in North America is milled to a spring angle, the angle between the back of the molding and the wall once it is installed. Three values cover almost all stock profiles.
| Spring angle | Also called | Prevalence | Ceiling complement |
|---|---|---|---|
| 38° | "52/38 crown" (the 52° is the ceiling side) | Most common stock profile | 52° |
| 45° | "45/45 crown" | Common; symmetric profile | 45° |
| 52° | "38/52 crown" (reversed) | Less common, taller profiles | 38° |
The single most expensive habit in crown work is reading the complement off the ceiling, then entering it as the spring angle. The spring angle is measured from the wall. A 38° profile reads 52° against the ceiling, and entering 52 sends every miter and bevel after it wrong.
Saw settings by corner angle
At a true 90° corner the three stock profiles land on three different setting pairs, rounded to one decimal below. That spread is why the “set both to 45” shortcut only ever works for one specific profile.
| Spring angle | Miter | Bevel |
|---|---|---|
| 38° | 31.6° | 33.9° |
| 45° | 35.3° | 30.0° |
| 52° | 38.2° | 25.8° |
But drywall corners drift. Framing settles and joint compound builds up in the inside angle, so a corner that looks square commonly reads 88° or 92°. These tables give the inside-corner miter and bevel as the measured corner walks from 85° to 95°.
Spring 38°, by measured corner
| Corner | Miter | Bevel |
|---|---|---|
| 85° | 33.9° | 35.5° |
| 88° | 32.5° | 34.5° |
| 90° | 31.6° | 33.9° |
| 92° | 30.7° | 33.2° |
| 95° | 29.4° | 32.2° |
Spring 45°, by measured corner
| Corner | Miter | Bevel |
|---|---|---|
| 85° | 37.7° | 31.4° |
| 88° | 36.2° | 30.6° |
| 90° | 35.3° | 30.0° |
| 92° | 34.3° | 29.4° |
| 95° | 32.9° | 28.5° |
Spring 52°, by measured corner
| Corner | Miter | Bevel |
|---|---|---|
| 85° | 40.7° | 27.0° |
| 88° | 39.2° | 26.3° |
| 90° | 38.2° | 25.8° |
| 92° | 37.3° | 25.3° |
| 95° | 35.8° | 24.6° |
A 2° corner error shifts the miter by roughly a degree, which is enough to open a business-card gap in trim at eye level. For an outside corner the same formulas run on (360 − C) in place of the measured corner; at a square outside corner the saw-setting magnitudes match the inside values, only the blade swings the other way.
Compound miter formulas
The closed-form trig that produces every value above. φ is the spring angle from the wall, C is the measured corner angle.
Miter: M = arctan( sin φ ÷ tan(C / 2) )
Bevel: B = arcsin( cos φ × cos(C / 2) )Outside corner: substitute (360 − C) for C and run the same two equations. Worked example for a 45° profile on an 88° inside corner:
C / 2 = 44°
tan 44° = 0.9657
sin 45° = 0.7071
M = arctan(0.7071 ÷ 0.9657) = arctan(0.7322) = 36.2°
cos 45° = 0.7071
cos 44° = 0.7193
B = arcsin(0.7071 × 0.7193) = arcsin(0.5086) = 30.6°Stock and saw orientation
Crown ships long, so a blown cut wastes a long board. Plan order quantity against these standard lengths.
| Stock length | Typical material | Note |
|---|---|---|
| 8 ft | MDF, primed pine, polystyrene | Most common retail length |
| 12 ft | Pine, poplar, MDF | Fewer seams on long walls |
| 16 ft | Hardwood, MDF | Reduces splices on long runs; awkward to transport |
Order about 10–15% over the measured linear footage. Inside corners consume length on both pieces, outside corners need extra return stock, and a saw blade removes roughly 0.1 in of kerf per pass, so the cut list never sums exactly to the wall measurement.
The angles are only half the cut. These miter and bevel settings are for cutting flat: the crown lies on its back on the saw table, decorative face up, and the bevel tilt recreates the spring angle, so nothing leans against the fence.
| Element | Where it goes |
|---|---|
| Back of the molding | Flat on the saw table |
| Decorative face | Up, toward you |
| Ceiling edge of the molding | Against the fence |
| Keeper piece (inside corner) | To the left of the blade for a left-hand wall, mirrored for the right |
Get the orientation wrong and the long point lands on the wrong end of the board, which is the fastest way to turn a foot of molding into offcut. Mark the keeper side before the blade comes down.
Related concepts
- Compound cut: any cut combining a miter (horizontal blade swing) and a bevel (blade tilt). Crown is the everyday example; hopper joints and roof valleys are others.
- Nested vs flat cutting: nested keeps the crown angled against the fence and needs only a miter on a single-bevel saw; flat lays the crown on the table and requires both miter and bevel set on the saw.
- Digital angle finder: the $30 tool that reads the actual corner. Every setting in these tables is only as right as the corner angle fed into it.
- Coping: an alternative to mitering inside corners, where one piece butts square and the other is cut to follow its profile with a coping saw. Hides corners that are badly out of square.
- Spring angle vs crown projection: spring angle sets the saw math; projection (how far the crown drops down the wall and out along the ceiling) sets layout and is a separate measurement.