Calculator · Panels & cutting
Miter Angle Calculator
Calculate miter settings for frames, trim, polygon projects, and angled joints.
Miter angle calculator
Simple flat miters only. Compound crown moulding and bevel-plus-miter calculations are not included in this phase.
Result
Enter a corner angle or polygon side count, then calculate the simple flat miter.
How it works
This calculator handles simple flat miters for frames, trim, boxes, and regular polygon projects. Corner mode uses the included finished angle between the two joined pieces; polygon mode derives that included angle from the number of sides in a regular frame.
Compound crown moulding, bevel angles, spring angles, and three-dimensional trim setups are outside this phase.
- Corner mode: miter cut from square = (180 - included corner angle) / 2.
- Corner mode: saw complement angle = included corner angle / 2.
- Regular polygon mode: corner angle = 180 - (360 / number of sides).
- Regular polygon mode: miter cut from square = 180 / number of sides.
- Regular polygon mode: saw complement angle = 90 - miter cut from square.
Worked example
A 90 degree corner gives a 45 degree miter cut from square.
A 120 degree included corner gives (180 - 120) / 2 = 30 degrees from square and a 60 degree complement. A 6-sided regular frame has the same 120 degree included corner and gives the same settings.
Common mistakes
- Confusing a miter angle with a bevel angle.
- Using the wrong saw convention for the saw scale or fence setup.
- Assuming real walls, frames, and stock are perfectly square.
- Skipping test cuts before cutting finished lumber/timber or trim pieces.
Common questions
Does this calculate compound crown moulding?
No. This phase covers simple flat miters only.
What is miter cut from square?
It is the saw rotation away from a square crosscut. For two equal cuts, subtract the included corner angle from 180 degrees and divide by two.
What is the saw complement angle?
It is 90 degrees minus the miter cut-from-square setting, equal to half the included corner angle for two equal cuts. It is useful for saws or setups that use the complementary scale.
Should I make test cuts?
Yes. Saw calibration, wall angles, blade deflection, and material movement can all affect the final fit.