Compound Miter Angle Calculator
Miter and blade-bevel settings for compound cuts — crown moulding (spring angle 38° or 45°), picture frames, boxes and planters with sloped sides — for any corner angle, with flat and nested cutting methods.
How it works
For pieces tilted at spring angle S meeting at corner angle C: miter = atan( sin S ÷ tan(C/2) ); bevel = asin( cos S × cos(C/2) ). For a box with sides sloped T from vertical, S = 90° − T
When a board leans as well as turns a corner — crown moulding against wall and ceiling, or the sides of a planter that splay outward — the joint needs both a miter (the table swing) and a bevel (the blade tilt), and the two settings depend on each other through the corner angle and the lean. The formulas are pure trigonometry, but the numbers are unintuitive: 38° spring crown on a square corner needs a 31.6° miter with the blade tilted 33.9°, which is why saw makers mark those detents. Out-of-square walls change both settings, so measure real corners. Cutting the crown “nested” at its installed angle against the fence needs only a simple miter but demands a tall fence and a saw with enough capacity; laying it flat with compound settings works on any saw.
Worked example
Standard 38° spring crown on a 90° corner: miter 31.62°, bevel 33.86°. A four-sided planter with sides leaning 15° needs a 43.1° miter and 14.5° bevel.
Frequently asked questions
Which piece gets the bevel to the left?
With the crown’s ceiling edge against the fence and the blade tilted left: inside corners — left piece miter right, right piece miter left; outside corners the reverse. Cut a labelled test pair and keep them as a reference.
How do I find the spring angle of my crown?
Set the moulding in a square with both flats seated; the angle between the wall flat and the back is the spring angle — 38° (52° to the ceiling) and 45° are the two common profiles.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.