Miter angle calculator
The cut angle for joining two pieces at a corner.
Fill in the fields and the result will appear here automatically.
Calculates a symmetric flat joint of two equal-width pieces at an angle greater than 0 and less than 180°. The cut angle is measured from the piece’s lengthwise axis. A separate row gives deviation from a crosscut, suitable for a scale where a square crosscut is zero. Check your saw’s scale convention.
How it works
Formula and logic
Cut angle α=θ/2; saw deviation from a crosscut β=(180°−θ)/2=90°−α. θ is positive and finite, strictly below 180°; fractional degrees are allowed. Pieces are mirrored. Unequal-width joints, spatial compound cuts and reflex angles θ≥180° are not calculated.
Example
A 90° corner gives the classic mitre: a 45° cut, and 45° on the saw too.
Fields and units
- Corner angle — °
How to use
- — Measure the actual wall angle with a protractor: in real rooms a right angle is rarely exactly right.
- — The mitre saw scale takes the "saw setting from 90°" row, not the cut angle itself.
- — The two pieces are cut mirrored: one to the left, one to the right of the same setting.
- — Crown moulding sitting at a tilt also needs a bevel angle — a flat cut by this formula will leave a gap.
Method and limitations
- Calculation method
- Formula and logic
- Limitation
- Unequal-width joints, spatial compound cuts and reflex angles θ≥180° are not calculated. Check your saw’s scale convention.
FAQ
Why is the saw number different?
The saw row is deviation from a square crosscut, which is 0° on the assumed scale. A cut at 67.5° from the lengthwise axis means a 22.5° deviation; for θ=90° both happen to be 45°.
Why does the cut not meet in a real corner?
Because walls are rarely at a true 90°. Even two degrees out leaves a visible gap on wide skirting — which is why the angle is measured on site rather than taken off a drawing.
Does this cover crown moulding?
Only for a flat cut. Crown sits tilted to both surfaces and needs a compound cut — the mitre angle together with a bevel angle on the saw.
What about a very sharp corner?
The same geometry applies for 0<θ<180°, but tool range and how the cut is made depend on the saw and piece. There is no universal rule to replace the joint at 30°.