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Cuts

Miter Angle Calculator

The miter cut for any corner, square or not.

Your measurementsEvery assumption editable01

Measure the actual corner — walls are almost never the 90° they look.

Two for a normal corner. More only for an unusual joint.

Miter cutCalculated live02

Result

45° saw setting

Cut each piece at 45° — saw scale reads 45°

Corner anglean inside corner
90°
Pieces meeting
2
Angle per piecethe corner divided between the pieces
45°
Saw scale settingmeasured off square, as mitre saws read
45°

Each piece takes half the corner, not the whole of it. A 90° corner needs two 45° cuts, and the commonest error is setting the saw to the corner angle rather than to half of it.

Mitre saws read off square, so a 45° cut appears as 45 on the scale but a 22.5° cut appears as 67.5. Both figures are given because tools disagree about which they display.

Measure the corner rather than assuming it. Walls out by two or three degrees are entirely normal, and a mitre cut to a theoretical 90° leaves a gap you will spend longer filling than measuring would have taken.

Each piece takes half the corner, not the whole of it. Measure the actual angle — walls are almost never the 90° they appear — and this gives both the cut angle and what your saw scale should read.

Why use this tool?What it does differently03

Why use this tool?

Any corner

Inside, outside, or anything between. Bay windows and older houses are rarely square.

Saw scale figure

What the tool actually reads, alongside the true cut angle.

The halving

The commonest error is setting the saw to the corner angle rather than to half of it.

More than two pieces

For unusual joints where three or more members meet.

How this worksThe method04

How this miter angle calculator works

Two pieces meeting at a corner each take half of it. A 90° corner needs two 45° cuts; a 135° octagon corner needs two at 67.5°.

Mitre saws measure off square rather than from the face, so the scale reads 90 less the cut angle. At 45° the two happen to coincide, which is why square corners feel intuitive and everything else does not.

Measuring the corner beats assuming it. Walls out by two or three degrees are entirely normal, and a mitre cut to a theoretical 90° leaves a gap that takes longer to fill than measuring would have taken.

How to use itStep by step05

How to use it

  1. Step 1: Measure the corner

    With an angle finder or a bevel gauge and a protractor. Do not assume 90.

  2. Step 2: Halve it

    Each of the two pieces takes half. This does that and shows both conventions.

  3. Step 3: Set the saw

    Using the scale figure, which is measured off square.

  4. Step 4: Check with an offcut

    Two scrap pieces cut and held together will show any error immediately.

Example usageWorked figures06

Example usage

A square corner
90° gives 45° per piece, and the saw scale also reads 45 — the one case where the two conventions coincide.
An octagon corner
135° gives 67.5° per piece but the saw reads 22.5. Setting 67.5 on the scale would be badly wrong.
A real-world wall
A corner measuring 87° gives 43.5° per piece, saw scale 46.5. Three degrees of wall error is completely normal and entirely visible if ignored.
Frequently asked questionsCommon questions07

Frequently asked questions

What angle do I cut for a 90 degree corner?

45 degrees on each of the two pieces. The saw scale also reads 45, which is the only angle where the cut and the scale figure match.

How do I miter a corner that is not square?

Measure the actual angle and halve it. A corner of 87° needs two cuts of 43.5°, which reads 46.5 on a mitre saw scale.

Why does my saw scale not match the angle I calculated?

Saws measure off square rather than from the face, so the scale shows 90 less the cut angle. Both figures are given here.

How do I measure a corner accurately?

A digital angle finder is quickest. Otherwise set a sliding bevel to the corner and read it against a protractor — more reliable than trying to measure in place.

Do inside and outside corners differ?

The arithmetic is identical; what changes is which face of the cut is long. Mark the long point before cutting and the two are hard to confuse.

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