Woodworking calculator
Compound Miter Calculator
Find the paired miter and bevel settings for sloped trim, tapered boxes, crown style work, and other compound joints.
Sage’s guided lesson
Let’s understand the result before using it
Calculate miter and bevel saw settings for compound joints from corner angle and workpiece slope, with setup and verification tips. I’ll show you what the numbers mean, how to check the math yourself, and where real-world conditions can change the answer.
Start with the real job
What this calculator is actually doing
A compound joint turns in two planes at once. The corner angle controls the turn seen from above, while the slope controls how far the workpiece leans from level. The calculator resolves those two angles into a saw table miter and blade bevel.
Define the included corner and the slope from the saw table exactly as the calculator describes; crown spring angle is measured differently.
Now for the arithmetic
How to do the math yourself
The calculation first finds the flat miter, F = (180° − C) ÷ 2, where C is the included corner angle. With workpiece slope S measured up from the saw table, the saw settings are miter = arctan(tan(F) × cos(S)) and bevel = arcsin(sin(F) × sin(S)).
Worked example
Use a 90° included corner and a 38° slope from the saw table.Flat miter F = (180° − 90°) ÷ 2 = 45°Miter = arctan(tan 45° × cos 38°) = 38.23°Bevel = arcsin(sin 45° × sin 38°) = 25.84°Cut two scrap pieces in the intended orientation, then check the assembled corner.Set the saw from the calculated values, but expect the scale and detents to limit how closely the angles can be reproduced.
I know this is off topic, but this reminds me of a joke I heard when teaching this to one of my interns, What do you call a sad strawberry? A blueberry. Yeah, I don’t see the connection either, but I think it is cute!
Before you cut, mix, or order
Tips, shortcuts, and mistakes to avoid
- Confirm whether your saw scale reads zero with the blade square or uses the complementary angle.
- Label the face, top, and wall side of every piece before cutting; mirrored parts are easy to reverse.
- Real walls and boxes are rarely perfect, so measure the actual included corner rather than assuming 90 degrees.
A small corner error, reversed part, or wrong face against the fence can spoil a mathematically correct compound cut.
How we got here
A little history and background
Traditional carpenters solved compound cuts with full size layout, bevel gauges, and tables. Compound miter saws made the cuts faster, but the geometry did not change; modern calculators simply perform the same trigonometry instantly.
What the result does not tell you
The result assumes straight stock, an accurate saw, and a precise corner and slope measurement. Spring angle conventions, nested cutting, flat cutting, and manufacturer scale markings can change how the answer is entered at the saw. A common 38° crown spring angle corresponds to a 52° slope from the saw table when the molding is laid flat.
Frequently asked questions
Why are there two saw settings?
The miter turns the cut across the face, while the bevel tilts the blade through the thickness.
Can I assume every corner is 90 degrees?
No. Measure the actual included angle when fit matters.
Why should I test on scrap?
A correct calculation can still be offset by saw calibration, stock orientation, corner error, and the way the saw scale is labeled.
That wraps up the lesson
Class is over. It is officially cheese fries time.
You now know more about how the Compound Miter Calculator actually works, not just which buttons to press. That earns cheese fries, Sage’s favorite way to celebrate a finished lesson.
Before you use the result
Verify corner convention, slope convention, stock orientation, saw calibration, and a scrap test before cutting finished material.