Miter & Bevel Angle Calculator

Frequently Asked Questions

How do I find the miter angle for a regular polygon?

Each miter is 180 ÷ N degrees, where N is the number of sides. A hexagonal frame (6 sides) needs 180 ÷ 6 = 30° miters, and a typical 4-sided picture frame needs 180 ÷ 4 = 45°.

How do I miter an arbitrary (non-90°) corner?

Bisect the corner angle: miter = corner angle ÷ 2. A 120° wall corner is mitered at 60° on each piece, and any two miters at a joint must sum to the corner angle.

How does that relate to the saw's blade-tilt scale?

Many miter saws read the complement of the cut, so the scale shows 90° − miter. A 30° miter (hexagon) is set as 60° on a scale that measures from the fence, which is why hexagons feel "backwards" on some saws.

Why do my 45° miters leave a gap?

Usually the corner is not actually 90°, or the two pieces are not the same length on their long edge. Measure the real corner with a bevel gauge, divide by 2 for each miter, and check that the saw fence is square to the blade.

Provided by AllCalculators.io
Free online calculators for everyday. No registration required.

Estimates for informational purposes only.

Important Disclaimer: Estimates for informational purposes only.

This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

JavaScript is required to use the interactive calculator above. The questions and answers below remain readable without JavaScript.

How This Calculator Works

A clean mitered joint requires the two mating pieces to each be cut at exactly half the angle the corner turns through. For a regular closed frame - a picture frame, an octagon planter, a hexagon box - the exterior turn at every corner is 360° ÷ N, so each piece is cut at half of that: miter = 180° ÷ N. For a single non-square corner (a bay window returning at, say, 135°) the joint simply bisects the corner: each piece is cut at corner ÷ 2. This tool also gives the blade-tilt complement - the 90° − miter value - because a table-saw blade or a sliding saw set by tilt rather than by miter gauge reads the complement of the chop-saw scale. Switch modes for a regular polygon or an arbitrary corner.

Formula / Method

Regular polygon: interior angle = (N − 2) × 180° ÷ N; the exterior (turn) angle = 360° ÷ N; the miter cut on each end = 180° ÷ N. The two miters meet to form the full joint angle = 360° ÷ N. Arbitrary corner: the cut on each piece = corner ÷ 2. The table-saw blade-tilt complement = 90° − miter, used when the cut is made flat on the table with the blade tilted rather than upright against a miter gauge. A square (4-sided) frame gives 180 ÷ 4 = 45°, the familiar picture-frame number, confirming the formula.

Worked Example

A hexagonal planter has N = 6 sides. Miter = 180 ÷ 6 = 30°, so set the chop saw 30° off square; each joint closes to 2 × 30 = 60° and the interior angle is (6 − 2) × 180 ÷ 6 = 120°. The table-saw blade-tilt complement is 90 − 30 = 60°. For an octagon, miter = 180 ÷ 8 = 22.5°. For a single bay-window return where the wall turns through 135°, each trim piece is cut at 135 ÷ 2 = 67.5°. Cut every piece from the same gauge setting and a test scrap first - a 0.5° error per cut multiplies across many corners into a visible gap.

Common Mistakes

Confusing the miter-saw scale (degrees off 90°) with the included joint angle - the saw reads the cut angle, not the corner.

Setting the table-saw blade tilt to the miter value instead of its 90° complement.

Cutting all pieces with the saw set one way so mirrored ends do not pair; alternate the stock face or the gauge direction.

Assuming an "90° corner" in an old house is actually square - measure the real angle; walls drift several degrees.

Ignoring blade kerf and stop-block placement, so finished pieces come out a hair short and the frame will not close.

Tips & FAQ

Why won't my picture frame close? Almost always cumulative miter error: four corners at 45.3° instead of 45° leaves a visible gap. Cut and dry-clamp all four pieces and tweak the saw a fraction at a time. How do I find a real wall corner angle? Use an angle finder or protractor against the two walls, then halve that reading for each trim piece. Spring-back on tight miters? A whisker under 45° (e.g. 44.8°) closes the outside of the joint tight, which reads better than a gap. Long pieces? Set a stop block so every piece is identically long; equal lengths matter as much as equal angles for a frame to close square. Compound corners (crown molding)? A piece that also leans away from the wall needs a compound miter and bevel - use the dedicated compound-miter calculator, not this flat-cut tool. End grain on miters? Mitered corners are largely end-grain glue joints and are weak; reinforce with splines, biscuits, dominoes, or keys for anything that takes stress. Always confirm with a scrap test cut before committing your final stock - it costs one offcut and saves a whole project.

Miter & Bevel Angle Calculator

Frequently Asked Questions

Related Woodworking Calculators