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Woodshop Math

Calculator

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.

After you calculate, print and download options will appear.

Result

Enter a corner angle or polygon side count, then calculate the simple flat miter.

These results are estimates only. Verify measurements, material specifications, structural requirements, safety requirements, and local building rules before buying materials or building.

How this calculator works

This calculator handles simple flat miters for frames, trim, boxes, and regular polygon projects. It can work from a known corner angle or 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.

Formula

  • Corner mode: miter cut from square = corner angle / 2.
  • Corner mode: saw complement angle = 90 - miter cut from square.
  • 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 4-sided frame also gives a 45 degree miter cut. A 6-sided regular frame gives a 30 degree miter cut from square.

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.

FAQs

Does this calculate compound crown moulding?

No. This phase covers simple flat miters only.

What is miter cut from square?

It is the angle that splits the corner evenly from a square end cut, such as 45 degrees for a 90 degree corner.

What is the saw complement angle?

It is 90 degrees minus the miter cut angle, useful for saws or setups that reference the fence or complementary scale.

Should I make test cuts?

Yes. Saw calibration, wall angles, blade deflection, and material movement can all affect the final fit.

Calculator disclaimer

These results are estimates only. Verify measurements, material specifications, structural requirements, safety requirements, and local building rules before buying materials or building.