Compound miter calculator
Calculate blade tilt and miter angle for crown molding and other compound cuts.
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Crown molding sits at an angle between the wall and ceiling — the spring angle. To cut a joint at a corner, you need two angles set on the saw simultaneously: the miter angle (turntable/fence setting) and the blade tilt (bevel setting).
Most crown molding is either 38° or 45° spring angle. The most common corner is 90° (square). For non-square corners (bay windows, angled walls), measure the actual corner angle and enter it here.
Cutting crown molding flat on a miter saw requires two angles: the miter angle (the rotation of the saw blade left/right) and the bevel angle(the tilt of the blade). These aren't the same as the wall corner angle because crown molding sits at an angle to the wall — the spring angle. A 38° spring crown on a standard 90° corner needs a miter of 31.6° and a bevel of 33.9°, not the 45° you'd use for flat trim. Get these angles wrong and your corners won't close.
Tips
- Check the spring angle on the molding profile — it's printed on the back of most stock
- Always cut test pieces from scrap before cutting the real material
- For outside corners, reverse the miter angle direction
- Measure actual corner angles with a digital protractor — walls are rarely exactly 90°
FAQ
What angle do I cut crown molding at?
For standard 38° spring crown on 90° inside or outside corners, cut with a miter angle of 31.6° and a bevel angle of 33.9°. For 45° spring crown on 90° corners, use a miter of 35.3° and a bevel of 30°. These are the angles when cutting the molding flat on the saw table. Cutting nested (against the fence) uses different angles — 45° miter, 0° bevel — but requires the molding to be properly positioned against the fence.
What is spring angle?
Spring angle is the angle between the back of the crown molding and the wall. The two most common spring angles are 38° and 45°. You can find your molding's spring angle by looking at the manufacturer's spec sheet, or by measuring the width of the flat back surfaces that contact the wall and ceiling — a 38° crown has a wider wall flat than ceiling flat, while a 45° crown has equal flats.
Why are my crown molding corners not closing?
The most common cause is using the wrong spring angle in your calculations — assume 38° when it's actually 45° and the gap will be visible. Other causes: cutting the molding upside down or backwards, not accounting for out-of-square corners (measure the actual wall angle with a digital angle finder), or wall corners that aren't truly 90°. Always test-fit a small scrap piece before cutting your finish material.
What is coping crown molding and when should I use it?
Coping is an alternative to mitering inside corners where you cut the first piece of crown square against the wall, then cut the second piece to match the profile of the first using a coping saw. Unlike mitered inside corners, coped joints stay tight even when the walls shift seasonally or aren't perfectly square — which is almost always the case in real houses. Professional trim carpenters cope every inside corner as standard practice. Outside corners are always mitered — coping only applies to inside corners.
How do I cope crown molding with a coping saw?
First, cut the first piece square (butted flat against the wall). Then cut the second piece with a 45° inside miter cut on your miter saw — this exposes the profile you need to follow. Using a pencil, trace the profile line along the front edge of the molding where the cut meets the face. Now take your coping saw and cut along that traced line, angling the blade back slightly (5-10°) to undercut the joint — this creates a knife-edge that tucks tightly against the first piece. Test-fit, file or sand any tight spots with a rat-tail file, and install.
Coping vs mitering inside corners — which is better?
Coping is almost always better for inside corners. Mitered inside corners require both walls to be perfectly 90° and both pieces to be cut at exactly 45°. Any deviation creates a visible gap. Coped joints are forgiving because only the front face needs to match the profile. The one downside is speed — a coped joint takes 5-10 minutes versus 30 seconds for a miter — but the quality difference on finish work is worth the extra effort. For paint-grade work where you'll fill gaps with caulk, mitered inside corners are acceptable. For stain-grade work, always cope.