Linear feet with coped-corner waste & board count
Crown molding is trim installed at the wall–ceiling joint, cut at a compound angle so it "springs" against both surfaces. The molding's cross-section is defined by its spring angle — the angle it rotates from horizontal when installed. The two common spring angles are 38°/52° and 45°/45°, describing how the profile splits between wall and ceiling contact. You must set your saw to match the molding's spring angle or the joints will not close.
Inside corners can be coped — one piece runs square into the corner and the other is cut with a coping saw along its profile so it nests over the first. Coping produces tighter, longer-lasting inside corners than mitering because walls rarely meet at exactly 90°. Coped joints take extra material and time, which is why installers add a waste factor of 10–20% to linear feet.
For a 90° inside corner with 45/45 crown laid flat in a miter saw (matching most DIY saw setups), each piece is cut at 45° miter. For 38/52 crown in a 90° corner, the miter is still 45° but the bevel changes to about 33.9° when cutting the molding flat, per standard crown molding charts. For out-of-square corners, measure the actual angle, divide by 2, and set the miter to the half-angle.
When the molding is nested against the saw fence at its installed spring angle (rather than laid flat), the miter setting equals half the corner angle directly, and no bevel compensation is needed — this is why many pros build a simple fence jig.
The table below shows the common spring angle profiles and their typical miter/bevel settings for 90° corners cut with the molding laid flat.
| Spring angle | Typical use | Miter (flat cut, 90° corner) | Bevel (flat cut, 90° corner) |
|---|---|---|---|
| 45°/45° | Many common profiles | 45° | 0° (miter only) |
| 38°/52° | Most big-box molding | 45° | ~33.9° |
Measure each wall and sum the lengths; do not subtract for inside corners because coped joints overlap. Add 10–20% waste for coped corners, splices, and defect cuts — longer walls need a splice scarf joint cut at 45° in the molding run. Order by the linear foot, and buy an extra full length if your total is close to a whole number of pieces.
Standard molding lengths run 8 to 16 feet. Plan splices to fall between wall studs if possible, and pre-finish or paint before installation to reduce touch-up on the ceiling line.
Crown installs against walls and ceilings that are rarely flat. Before cutting, check corners with a framing square: out-of-square corners change the miter angle from 45° to the measured half-angle, and a corner 3° off square visibly opens a mitered joint. Wavy walls produce gaps along the top edge; many installers cope the top contact line or caulk after installation, which paint hides but which is easier on smaller gaps.
Fastening is typically to the wall studs and ceiling joists with finish nails — two 8d nails at stud locations is a common pattern — with construction adhesive reducing nail count on irregular surfaces. Long runs need scarf joints (a 45° overlapping cut) placed between supports, glued and nailed through the overlap so the joint moves as one piece.
Outside corners mirror inside corners but are almost always mitered rather than coped, because a coped joint only nests on an inside corner. Walls that bow outward create gaps at outside miters; walls that bow inward make the joint bind. Dry-fitting each piece before nailing catches these issues while the piece can still be recut, and numbering the back of each piece against a sketch of the room keeps a long installation organized.
What is a spring angle in crown molding?
It is the angle the molding rotates from the wall/ceiling plane when installed — the angle between the molding's back and the wall. Common profiles are 38°/52° and 45°/45°, and your saw settings depend on which you have.
How do I find my molding's spring angle?
Measure the angles on the back of the molding: the two beveled contacting surfaces meet the wall and ceiling. If they sit at 45° and 45° it is a 45/45 profile; if 38° and 52°, it is 38/52 — the two most common standards.
Why cope inside corners instead of mitering them?
Coped joints nest one profiled end over a square-cut piece, absorbing wall irregularities. Walls rarely meet at exactly 90°, so miters open over time; copes stay tight, at the cost of more cutting time and slightly more material.
What waste factor should I add for crown molding?
10–20% is typical: coped corners overlap, splices need scarf cuts, and some lengths are lost to defects. The high end applies to rooms with many corners.
Can I cut crown molding standing up in the saw?
Yes — if you nest the molding against the saw fence at its spring angle, the miter setting is simply half the corner angle and no bevel compensation is needed. Cutting flat requires the miter/bevel pairs shown in the table above.