Layout model and usable dimensions
A corner angle and a miter-saw scale reading are different measurements. This calculator finds equal flat miters for two matching pieces that meet at a measured interior corner, or for all corners of a regular polygon. The saw setting is measured away from a square crosscut. It also reports the angle on each cut face so you can check which convention your measuring tool uses. This is a two-dimensional flat-joint calculation, intended for trim lying in one plane. Crown molding, tilted workpieces, and compound bevel cuts require additional geometry.
Fit, direction and offcut constraints
- Inside and outside corners need mirrored cut directions even when their numeric saw setting is identical.
- Irregular polygons require each actual corner angle rather than a shared side count.
- This flat-miter result does not calculate bevel settings or a safe setup for every saw or workpiece.
Layout arithmetic and example
A worked example
A measured 90° interior corner gives a 45° saw setting. In regular-polygon mode, six sides produce a 30° saw setting.
Measure and compare a layout
- Select a measured interior corner or a regular polygon.
- Enter the corner angle, or the number of equal polygon sides.
- Set opposite-handed equal miters and verify the joint with scrap before final cuts.
Frequently asked questions
What miter angle makes a 90 degree corner?
Two equal flat miters use a 45 degree saw setting away from a square cut.
What saw angle do I use for a hexagon frame?
A regular hexagon has a 120 degree interior angle, so equal joints use a 30 degree miter-saw setting.
Can I use this for crown molding?
Only for a flat joint in one plane. Crown molding held or laid at an angle can require a separate compound-miter calculation.
Read the project guides
- How to Plan a Cut List with Saw Kerf, Offcuts and Stock Lengths
Plan repeated lumber cuts using actual stock lengths, end trimming, kerf, whole-board rounding, and realistic offcut reuse.
Calculation method: JICWH methodology. Examples are planning assumptions, not product recommendations.