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A4 · Woodworking calculator

Mitre Angle Calculator for Corners & Frames

Calculate two equal flat mitres for a measured inside corner or plan a regular multi-sided frame. Results distinguish the saw adjustment from square from the cut line measured along the workpiece.

Free to use · no account needed · calculations stay in this browser · formula reviewed 4 September 2026

Choose the calculation type

Corner mode joins two equal flat pieces. Regular-frame mode calculates equal mitres for a polygon.

Calculation type

For a two-piece inside corner C, saw adjustment from square = (180° − C) ÷ 2. The cut line measured from the long edge = C ÷ 2. For a regular n-sided frame, saw adjustment = 180° ÷ n.

Example result using the values shown

Saw adjustment from square
45°
Cut line from the long edge
45°
Finished inside corner
90°
Joint
Two equal flat mitres form the entered inside corner.

The numeric adjustment is a geometry check, not a prescribed machine direction. Confirm the reference face, waste side and saw scale.

  • Two equal flat pieces form a 90° inside corner.
  • Angles are nominal and do not include fitting corrections.

Read the two angle conventions

A mitre saw normally reads 0° for a square crosscut, so the calculator reports the adjustment away from square. A drawing may instead show the cut line from the workpiece's long edge. Those two values add to 90°.

For a 120° inside corner, the saw adjustment is 30° and the cut line is 60°. A regular hexagon has the same 120° inside corner, the same 30° saw adjustment and the same 60° cut line.

What this calculator does not cover

Sprung moulding, bevel settings and three-dimensional joints are not approximated here. Use the separate compound mitre calculator for cornice only for sprung moulding cut flat on the saw table.

Corner sketch

Finished inside corner_____°
Saw adjustment from square_____°
Cut line from long edge_____°
Reference face / waste side____________________