What is the miter angle for a standard 90-degree corner?

45 degrees on each piece. Equal-width boards split the joint angle evenly, so a 90-degree corner gives 90 / 2 = 45 degrees per side.

Why are the two miter angles different when the boards are different widths?

To keep the outer corner point aligned, a narrower board must be cut at a smaller angle than a wider board meeting it at the same corner — cutting both at a flat 45 degrees only works when the two boards match in width.

How much does it cost to have a mitered joint cut and fitted professionally in Canada?

A carpenter in Canada typically charges around CAD 110-370 for a single mitered trim or molding joint, depending on the molding profile, the material, and whether a compound (crown molding) cut is required.

Miter Angle Calculator — Saw Angle for Corner Joints

Miter Angle Calculator: Corner Cut Angle for Trim and Molding

When two pieces of trim, molding, or picture-frame stock meet at a corner, each piece is cut at half the corner's angle so the two cut faces sit flush together — a square 90-degree corner needs a 45-degree miter on each side. Real corners are not always exactly 90 degrees, and the two boards are not always the same width, so this calculator takes the actual joint angle and each board's width and returns the exact miter angle and saw dial setting for every piece.

How to use the miter angle calculator

Enter the joint angle — the actual angle of the corner, in degrees. Use 90 for a standard square corner, or measure it with an angle finder if the wall is out of square.
Enter the width of each board. Leave them equal if both pieces match, or enter each width separately for an asymmetric joint.
Read off the miter angle and saw dial setting for each board — the number to set on the saw's angle scale, measured from the straight-through 90-degree position.

The miter angle formula

For equal-width boards, each miter angle is simply half the joint angle: miter angle = joint angle / 2. A 90-degree corner needs a 45-degree cut on each piece (90 / 2 = 45); a 120-degree corner needs 60 degrees on each piece.

When the boards differ in width, the angle is no longer split evenly: the narrower board takes the smaller angle, found from narrower angle = arctan(n × sin(theta) / (m + n × cos(theta))), where m and n are the wider and narrower widths and theta is the joint angle. The wider board takes the rest of the joint angle, and each saw dial setting equals |90 - miter angle|.

Tips

Crown molding sits at an angle to the wall and ceiling rather than flat, so a true corner needs a compound miter — the miter angle plus a bevel or spring angle — not the flat miter angle alone.

Cut a test joint in scrap first. Walls are rarely perfectly square, so treat the calculated angle as a starting point and fine-tune by a degree or two if the fit is off.

In Canada, a carpenter typically charges about CAD 110-370 to cut and fit a single mitered trim or molding joint, depending on the material and whether it is a simple flat miter or a compound crown-molding cut.