Crown molding angle calculator
Enter the spring angle and corner, get the saw settings.
What are the saw settings for crown molding?
For standard 38° (52/38) crown lying flat on the saw at a 90° corner: miter 31.62° and bevel 33.86°. For 45° crown: miter 35.26° and bevel 30°.
What is the spring angle?
The angle between the back of the molding and the wall. Common crown is 38° (sold as 52/38) or 45° (45/45).
How are the angles calculated?
Miter = atan(sin S ÷ tan(A/2)) and bevel = asin(cos S × cos(A/2)), where S is the spring angle and A the corner angle.
What about corners that are not 90°?
Enter the actual corner angle: for 38° crown at a 135° corner, the miter is 14.31° and the bevel 17.55°. Measure the corner with an angle finder first.
Are outside corners different?
The angles are the same as for the matching inside corner; only the direction of the cut on each piece changes.
How do I find the spring angle of my molding?
Read it from the package or profile drawing: crown sold as 52/38 has a 38° spring angle. With no label, hold an offcut in its installed position against a square corner and measure the angle between its back and the vertical face with a bevel gauge. Installers on the Woodweb forum note that the back, not the decorative face, sets the spring angle, and that a cupped back throws a compound cut off.
Should crown be cut flat or in position against the fence?
This calculator gives the flat settings, with the back on the saw table. Some finish carpenters on the Woodweb forum cut crown upside down in its installed position because they find it faster and more accurate, and keep flat cutting for molding too tall for the saw. In position the table and fence stand in for the ceiling and the wall, so the cut is a plain miter of half the corner angle: 45° at a square corner, with no bevel.
Where the formulas come from and where they stop
Crown molding leans out from the wall, so its cut face is tilted two ways at once. With the back flat on the saw table and the top edge against the fence, as in Bosch's manual, the blade has to follow the vertical plane that bisects the room corner, which gives the formulas above. They assume a flat back, plumb walls, a flat ceiling and a spring angle that is true for your piece. An outside corner is entered as the angle above 180° and gives the same two numbers as the matching inside corner.
Worked example
A 38° crown in a square, 90° inside corner: sin 38° = 0.6157 and tan 45° = 1, so the miter is atan(0.6157) = 31.62°. cos 38° = 0.7880 and cos 45° = 0.7071, so the bevel is asin(0.5572) = 33.86°. Bosch lists 31.6° and 33.9°. For 45° crown the same corner gives 35.26° and 30.00° (Bosch: 35.3° and 30.0°). If the corner really measures 92°, the settings become 30.73° and 33.19°, almost a degree off on the miter.
Common mistakes
Entering the wrong spring angle is the most common error: 52/38 crown has a 38° spring angle, and typing 52 returns 38.24° and 25.81° instead of 31.62° and 33.86°, a joint that will not close. Next, assuming every corner is 90°; measure each one. Then the directions: Bosch's tables give the same two numbers for inside and outside corners and for left and right ends, with the directions mirrored, so mark each piece. Finally, always make a test cut on scrap, as Bosch's manual says.
Sources: Bosch Power Tools, compound miter saw operating manual (model 4412), “Crown Molding Laying Flat on Table” (38° and 45° setting tables, spring angle, test-cut warning); Woodweb Knowledge Base, “Finding Compound Angles for Crown Moulding” (installers on cupped backs and cutting in position). The formulas are the geometry of the flat position and reproduce Bosch’s values. Related: baseboard calculator, framing calculator. How we check our calculators.