Miter Angle For a 4 Sided Box
45°
- 4-sided regular flat frame
Methodmiter angle = 180 / number of sides.
This is the FLAT-frame angle (no slope). For a sloped/flared version of the same box, see the compound-miter answers or the angle calculator.
45° — the setting every miter saw has a built-in detent for, and the one so familiar it barely needs looking up, included here mainly for completeness and so the 4-sided case sits alongside its less-obvious neighbours.
Why this one specifically
A 4-sided box or frame is the default shape for nearly everything — picture frames, drawer boxes, simple planters — and it's the one shape in the common polygon set where the flat-frame formula (180 divided by the side count) produces a number most people already have memorized, which is exactly why the odd side counts (5, 7, 9, 11) catch people off guard: they assume those follow some similarly "nice" pattern, and they don't.
What moves the number
The 45° figure holds only for a FLAT frame with no lean or flare — a tapered or flared 4-sided box (a planter with sloped sides, for instance) needs a compound miter and bevel instead, a different calculation entirely from this flat-frame case.
See the miter angles for common polygons explainer for the full table, compound miter angles for sloped work if your 4-sided project actually flares or tapers, and confirm the exact figure in the angle calculator.