Compound Miter Angle Calculator

Calculate miter and bevel angles for trim at non-90° corners

Project Details
Enter your measurements and requirements
Results
Calculated estimates for your project
Miter Angle38.24°
Bevel Angle25.81°
Corner TypeAcute (<90°)
Spring Angle Used38.0° (38° = crown, 52° = base cap)

Additional Information

About This Compound Miter Calculator

Our compound miter calculator determines the exact miter and bevel angles needed to cut crown molding, trim, and other materials at non-90-degree corners. Whether you're dealing with an obtuse corner in a bay window or an odd-angled wall, this tool eliminates the frustrating trial-and-error approach.

Compound miter cuts require setting both the miter (rotation) and bevel (tilt) angles on your saw. The calculations depend on the corner angle and the spring angle of your molding - the angle at which the molding sits against the wall and ceiling. Standard crown molding has a 38-degree spring angle, while some profiles use 45 or 52 degrees.

This calculator is essential for finish carpenters, DIYers installing crown molding, and anyone asking "what angle do I cut crown molding for a 135-degree corner?" or "how do I calculate compound miter angles?" The results work for any corner angle, not just common 90 or 45-degree cuts.

How to Use This Calculator

Follow these steps to calculate compound miter angles:

  1. Measure the corner angle using an angle finder or protractor
  2. Determine your molding's spring angle (38° is most common for crown)
  3. Enter both values into the calculator
  4. Set your miter saw to the calculated miter angle
  5. Set the bevel angle as indicated and make test cuts
Frequently Asked Questions

What is a spring angle in crown molding?

The spring angle is the angle between the back of the crown molding and the wall when installed. Most crown molding has a 38-degree spring angle (also called 38/52, meaning 38° from ceiling, 52° from wall). Some profiles use 45/45 spring angles. Check your molding packaging or hold it against a square to determine the spring angle.

How do I cut crown molding for a 90-degree corner?

For standard 90-degree corners with 38/52 crown molding, set your miter saw to 31.6° miter and 33.9° bevel. Alternatively, position the crown upside down and against the fence (nested cutting) and make simple 45° miter cuts with no bevel. The nested method is simpler but requires adequate saw capacity.

How do I measure an odd corner angle?

Use an angle finder tool placed against both walls to read the corner angle directly. Alternatively, use a bevel gauge against both walls and measure the angle with a protractor. Digital angle finders are accurate to 0.1 degrees. Remember that inside corners are typically less than 180°, and outside corners are greater than 180°.

Why don't my miter joints fit perfectly?

Common issues include: walls that aren't perfectly square (measure each corner), saw blade not calibrated to true 0°, incorrect spring angle assumed, or material movement. Always make test cuts in scrap material. Fine-tune angles by adjusting 0.5° at a time. Even slight errors compound across the joint.

Can I use these angles for baseboard at odd corners?

Yes, but baseboard sits flat against the wall with a 0° spring angle. For baseboard at non-90° corners, you only need a miter cut equal to half the corner angle (no bevel needed). For example, a 135° corner needs a 67.5° miter cut on each piece. Use the calculator with 0° spring angle for flat trim.

What saw do I need for compound miter cuts?

A compound miter saw can adjust both miter and bevel angles. A dual-bevel compound miter saw allows bevel cuts in both directions without flipping the workpiece. For large crown molding, a 10 or 12-inch sliding compound miter saw provides the capacity needed. Ensure your saw's bevel range covers the calculated angle.

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