Setting out and cutting
Mitred external corner: bevel angle and bevel width
- where
- bevel angle, blade tilt from square (°)
- angle between the two wall faces across the solid corner (°)
- bevel width across the back of the tile (mm)
- tile thickness (mm)
- square edge left on the face (mm)
Explain this equation
Gives the saw blade tilt for mitring tiles round an external corner, and how far the bevel runs across the back so you can mark it. Use it for porcelain boxings, window reveals and splayed corners.
A is the corner angle measured across the solid: 90° for a square boxing, 135° for a splayed one. The two tiles have to turn through 180° − A between them, so each takes half. The land is the small square edge left on the face so the arris does not chip.
Splitting the turn equally between the two tiles means both faces meet on the bisector of the corner. The bevel runs across the tile thickness, less the land, at angle β, so its width on the back is that thickness times tan β.
Sense check: a square corner needs 45° and, on a 10 mm tile leaving 1 mm land, the bevel runs 9 mm across the back. A 135° corner needs only 22.5°.
Watch out: saw scales are not always accurate. Cut a test pair from offcuts and check the fit before cutting good tiles.
Gives the saw blade tilt for each tile at a mitred external corner, and how far the bevel runs across the back of the tile so you can mark the cut.
Enter your values to see the result.
Good to know
A square external corner (A = 90°) needs each tile bevelled at 45°. A 135° corner (a splayed boxing) needs 22.5°. Leave a small square edge on the face (about 1 mm) so the arris does not chip and both faces meet cleanly; fill the small V with grout or a matching silicone. Mitres on through-bodied porcelain look clean; on glazed ceramic the biscuit shows, so use a trim.
Common mistake
Cutting the bevel to a sharp knife edge. It chips during cutting and handling and leaves a sharp, fragile corner that will not meet BS 5385 expectations for a safe finished edge.
Limits
Plane geometry for two wall faces meeting at a vertical corner. Compound mitres (corners that are also sloped) need a second angle. Saw scales and blade deflection vary, so test on an offcut.
Sources
Results are calculations from the published methods and manufacturer figures shown, and depend on the data you enter. Always follow the tile, adhesive and grout manufacturers’ instructions, BS 5385 and the Tile Association guidance. Coverage rates vary by product and substrate. Check prices and VAT rules with your own records and HMRC.