Bay window
Bay Window Miter Calculator
Flat stock against the wall — no bevel. Measure each corner; bays are rarely framed dead-on.
Quick answer
A standard 45° bay has 135° interior corners → cut each piece at 22.5°. A 30° bay (150° corners) cuts at 15°.
Why "45° bay" doesn't mean cut at 45°
The "45°" of a bay window describes how far the wall turns, not the saw setting. A 45° turn leaves a 135° opening at the inside of the corner, and the two trim pieces split that — so each is cut at 22.5°. It trips people up constantly. Enter the interior corner angle (the open angle you'd measure with an angle finder) and the calculator handles the rest.
FAQ
+What angle is a bay window corner?
Most bay windows turn at 45°, which makes a 135° interior corner — each piece is mitered at 22.5°. Some bays turn at 30°. Measure your actual corner to be sure, since older bays vary.
+How do I cut trim for a 45° bay window?
A 45° bay has 135° interior corners, so set the miter saw to 22.5° for each piece. Cut both mating pieces at that angle and the joint closes flat across the corner.
+My bay window corners are uneven — what now?
Bays are rarely framed perfectly. Measure each corner separately with an angle finder and cut each joint to its own number. Treat the calculator value as a starting point and fine-tune on scrap.
+Does this work for the window seat and sill too?
Yes. The corner angle is the same whether you are trimming the sill, the seat, or the casing — flat stock against the wall is a flat miter with no bevel.