Miter angle calculator
For flat trim — baseboard, door casing, chair rail nailed flat to the wall. Enter the corner angle and this halves it for you: no bevel, unlike crown molding, because flat trim never leaves the plane of the wall. Print the angle below as a true-size check.
90 for a square corner, measured with a protractor otherwise
Miter each piece at
45.0°
Bevel
0°
Miter check, at true size
Print at 100%, check the ruler, then register a bevel gauge or a cut offcut against the two lines to confirm the saw before you trust it on the good stock.
Put a tape on the printed ruler. If it does not read exactly 6 inches, the print was scaled — set the print dialog to 100% or “Actual size” and print it again. Do not cut wood from a template that failed this.
Baseline registers against your saw's fence or a straightedge; the second line is the miter cut.
Printing this properly
In the print dialog, set the scale to 100% or “Actual size” and turn off “Fit to page”. Measure the printed ruler with a tape before you trust the angle.
Worked example: a 90° corner
A 90° corner — a picture frame, a square box — is two pieces mitred at 45.0° each, with the blade square to the table.
Any other flat corner splits the same way. For a frame with equal sides:
- Triangle (60° corners)
- miter 60.0°
- Hexagon (120° corners)
- miter 30.0°
- Octagon (135° corners)
- miter 22.5°
- Twelve sides (150° corners)
- miter 15.0°
These are the figures the calculator above opens on. Change any field and it works the same problem for your numbers.
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About mitering flat trim
- What angle do I cut baseboard or casing for a corner?
- Half the corner angle. A square 90° corner miters at 45° on each piece; an open 135° corner — common where a bay or an addition meets the original wall at an angle — miters at 22.5°.
- Why doesn't this need a bevel setting like the crown molding calculator?
- Crown leans out from the wall, bridging it to the ceiling, so cutting it flat on the saw table needs a miter and a bevel together. Baseboard, casing and chair rail nailed flat never leave the plane of the wall — the joint is only ever a miter, and the bevel stays at zero the whole time.
- How do I find my actual corner angle?
- A digital angle finder reads it directly. Without one, hold a scrap of scrap trim in the corner as if it were the actual pieces, mark where the two overlap, and the angle between those marks — measured with a protractor or a speed square — is the corner. Most walls are close to 90°, but 'close' still shows up as a visible gap at the point of the miter.
You might also need
- Trim and baseboard calculatorLinear footage of flat trim for a room from its perimeter and its doorways, with a waste allowance.
- Crown molding anglesThe miter and bevel for any corner and any spring angle, plus the single setting for cutting it nested.
- 3-4-5 square checkThe diagonal that proves a corner square from any two leg lengths, scaled up for a full building corner.
- Door and window casingEvery head, leg and apron cut to its long point from the opening and the reveal, packed into the sticks you buy.
- Hexagon and octagon calculatorSide length, across flats and across corners from any one of them, for any regular polygon, with the area, the miter and each frame piece's cut lengths.