Compound Miter Calculator

1. Enter the spring angle of your moulding; standard crown is 38 degrees.
2. Enter the corner angle; a standard inside corner is 90 degrees.
3. Read the miter angle to set on the saw table.
4. Read the bevel angle to tilt the blade.

A compound miter is a cut that combines two angles at once: a miter across the face and a bevel through the thickness. It is needed whenever a joint is tilted rather than flat, most famously for crown moulding, which sits at an angle between the wall and the ceiling.

Cutting crown flat on the saw, rather than propped at its spring angle, means you must dial in both a miter and a bevel. Get either wrong and the corner will not close, so the exact pair of settings matters. This is the cut that intimidates most trim carpenters when they start out, purely because two angles have to be right at the same time rather than one.

1. Take the spring angle of the moulding and the corner angle of the wall.
2. The miter comes from the sine of the spring over the tangent of half the corner.
3. The bevel comes from the cosine of the spring times the sine of half the corner.
4. Set the table to the miter and tilt the blade to the bevel.

When the spring angle is 90 degrees, the moulding is flat and the bevel drops to zero, leaving a simple miter, which is why flat frames need no bevel.

Standard crown moulding has a 38 degree spring angle, cut for a 90 degree inside corner. The miter works out to about 31.6 degrees and the bevel to about 33.9 degrees. A 45 degree crown on the same corner needs a 35.3 degree miter and a 30 degree bevel. Cut flat trim, a 90 degree spring, and you get a plain 45 degree miter with no bevel at all.

Spring Angle

The angle the moulding sits at drives both settings; 38 and 45 degrees are the common crown spring angles.

Corner Angle

A tighter or wider wall corner shifts the miter and bevel; 90 degrees is the usual inside corner.

Inside vs Outside Corners

The angles are the same size, but the cut direction flips, so keep track of which way each piece faces.

Saw Reference

Saws vary in how they read miter and bevel, so confirm your machine matches the numbers.

Saw settings for common crown on a 90 degree corner.

These assume cutting the moulding flat on the saw; propping it at the spring angle uses a plain miter instead.

Fitting Crown Moulding

Get the miter and bevel to cut crown flat on the saw.

Sloped Boxes and Hoppers

Work out compound cuts for tapered, angled-side projects.

Odd Corners

Handle walls that are not a clean 90 degrees by entering the real corner angle.

1. Swapping Miter and Bevel

The table setting is the miter; the blade tilt is the bevel. Mixing them ruins the joint.

2. Wrong Spring Angle

Using 45 for a 38 degree crown, or the reverse, throws both settings out.

3. Ignoring Corner Angle

Walls are rarely perfect; measure the real corner for a tight fit.

4. Losing Track of Direction

Inside and outside corners flip the cut, so label each piece before cutting.

The trigonometry is exact for the spring and corner angles you enter, matching standard crown tables. It gives the angles, not which way to face each piece.

On a 90 degree inside corner, set a 31.6 degree miter and a 33.9 degree bevel to cut standard 38 degree crown moulding flat on the saw.

A cut that combines a miter across the face and a bevel through the thickness, needed for tilted joints such as crown moulding.

The miter is arctan(sin(spring) over tan(corner/2)); the bevel is arcsin(cos(spring) times sin(corner/2)), where spring and corner are the moulding and wall angles.

The angle a moulding sits at between the wall and ceiling. Standard crown is 38 degrees; a 45 degree crown is the other common type.

On a 90 degree corner, 45 degree crown needs a 35.3 degree miter and a 30 degree bevel.

At a 90 degree spring angle the moulding lies flat, so the bevel is zero and you are left with a simple 45 degree miter.

Yes. Walls are rarely exactly 90 degrees, and even a couple of degrees off changes the miter and bevel for a tight fit.

The angles are the same size, but the cut direction reverses, so mark each piece for inside or outside before cutting.

No. The calculator runs entirely in your browser and nothing you enter is stored or sent anywhere.

• Crown molding (Wikipedia).
• Miter joint (Wikipedia).
• Bevel (Wikipedia).