| Crown & corner | Flat miter | Flat bevel | Nested miter |
|---|---|---|---|
| 52/38, 90° inside/outside | 31.6° | 33.9° | 45° |
| 45/45, 90° inside/outside | 35.3° | 30.0° | 45° |
| 52/38, 135° corner (octagon) | 14.3° | 17.6° | 22.5° |
| 45/45, 135° corner (octagon) | 16.3° | 15.7° | 22.5° |
Measure the perimeter of the room, for a rectangle that is 2 × (length + width), then add 10 to 15 percent for miter cuts and mistakes. Divide the total by your stock length (8, 12 or 16 feet) and round up to get the number of pieces. Crown runs over doors and windows, so you do not subtract openings.
If you nest the crown upside-down against the saw fence at its spring angle, you miter each side at 45 degrees with no bevel. If you cut it flat on the table you need a compound cut: for standard 52/38 crown that is a 31.6-degree miter and a 33.9-degree bevel; for 45/45 crown it is a 35.3-degree miter and a 30-degree bevel.
The spring angle is how far the crown tips out from the wall. The two common profiles are 52/38 (52 degrees against the wall and 38 against the ceiling, the standard) and 45/45, which sits symmetrically. The spring angle sets both the compound miter and bevel, so identify it before cutting.
Add 10 to 15 percent to the measured perimeter. Crown wastes more than baseboard because every inside and outside corner needs a miter, and coped joints eat a few inches per cut. Rooms with many corners or short walls should use the higher figure.
Inside corners turn into the room (most rooms are all inside corners) and are often coped rather than mitered for a tight fit. Outside corners wrap a projection such as a chimney breast and must be mitered. The miter and bevel angles are the same size for a 90-degree inside or outside corner; only which side is waste changes.