How to use it
Count the sides
Enter the number of equal sides, 3 to 36: 4 for a square frame or box, 6 for a hexagon, 8 for an octagon.
Enter the slope
How far each side leans from flat: 0° for a picture frame lying flat, 90° for a box with upright sides, and in between for sides that splay. A side leaning 15° out from vertical has a 75° slope.
Read both settings
Miter is measured from square, bevel from vertical, which is how miter saw scales read. Set both and cut every end the same, the piece flat on the saw table.
Cut scrap first
DEWALT's manual says to make trial cuts and fit the pieces together before cutting the real ones.
The method
Miter and bevel for an n-sided frame or box
corner C = 180° − 360° ÷ n
miter = atan( cos t ÷ tan(C ÷ 2) )
bevel = asin( sin t × cos(C ÷ 2) )
- n
- number of equal sides
- t
- slope of each side from flat (degrees)
- C
- corner angle seen from above (degrees)
At t = 0 the miter is 180° ÷ n and there is no bevel; at t = 90° there is no miter and the bevel is 180° ÷ n. Crown molding is the same geometry with t = 90° − the spring angle.
| Case | Calculator | Reference |
|---|---|---|
| 4 sides, 26° slope | Miter 41.9°, bevel 18.1° | DEWALT's chart example: 42° and 18° |
| 4 sides, 45° slope | Miter 35.3°, bevel 30.0° | By hand: atan(cos 45°) = 35.26°, asin(sin 45° × cos 45°) = 30° |
| 6 sides, flat | Miter 30.0°, bevel 0.0° | 180° ÷ 6 |
| Crown, 52/38, 90° wall | Miter 31.6°, bevel 33.9° | Makita Table (A): 31.6° and 33.9°; DEWALT 31.62° and 33.85° |
DEWALT's example is read from a printed chart to the nearest degree. Makita's full crown tables, every wall angle from 60° to 180°, are checked in the tests behind this calculator.
Worked example: a splayed sleeve
Four sides leaning 15° outward have a 75° slope. The calculator gives a 14.5° miter and a 43.1° bevel. With 5 in wide sides, each leans in by 5 × cos 75° = 1.29 in over its width, so a 10 in top edge becomes a bottom edge of 10 − 2 × 1.29 = 7.41 in. The full build, with a drawing, is on miter saw projects.
What it cannot do
- Unequal sides or corners. The calculator assumes a regular shape. For a single corner of any angle, the crown calculator's wall angle does the same job for crown.
- Your saw's limits. A bevel above the saw's range cannot be cut flat: 49° on DEWALT's DWS779, 48° on Makita's LS1019. Check the setting against your saw before cutting.
- Better than the saw. Results show to 0.1°; a saw's scale and detents may not set that finely, which is why the makers insist on trial cuts.
Before cutting compound miters
- Sides counted and slope measured from flat
- Bevel within your saw's range
- Both settings locked, dry run done
- Trial pieces cut and fitted
- Every end cut with the piece the same way up
For crown molding on any wall angle, use the crown molding angle calculator. How the saw's miter and bevel work is in the miter saw guide.
Sources
The formulas are the standard ones for compound miters; they are checked against DEWALT's worked example (read from its chart, to the nearest degree) and against both of Makita's printed crown tables, 242 rows, of which 240 agree to the 0.1° Makita prints. Settings are shown to 0.1°, which is finer than most saw scales can be set; trial cuts settle the rest.
- 1.
Used for: A compound miter as a cut made with a miter and a bevel at once, for frames and boxes with slanting sides; its compound-miter chart and worked example — a four-sided box with 26° angles at a 42° miter and an 18° bevel — and the instruction to make trial cuts on scrap; miter scale 50° left and 60° right, bevel 49° each way.
- 2.
LS1019/LS1019L Slide Compound Miter Saw instruction manual, Mexico edition (Spanish section reviewed). Makita, 2025.
Used for: Printed crown tables for 52/38 and 45° crown at every wall angle from 60° to 180°, which the same formulas reproduce to the table's 0.1° rounding; miter 60° and bevel 48° each way on the LS1019.
About this calculator
Written by BenchRoot Editorial. How BenchRoot sources, checks and corrects its pages is set out in the Editorial Policy. If something here is wrong or unclear, the contact page explains how to tell us.