Miter Angle Calculator

Enter the corner angle and board widths to get exact miter saw settings, printable templates, and step-by-step tips.

Please enter a corner angle between 0° and 360°.
Board width must be a positive number.
Board width must be a positive number.
Board A Miter Angle
45.00°
Board B Miter Angle
45.00°
Miter Saw Setting
45.00°
Bevel Angle
0.00°
Set your miter saw to: 90° − 45.00° = 45.00°

Joint Diagram

Diagram will appear here

Miter Angle Guide & Instructions

Table of Contents

What is a Miter Angle?

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A miter angle is the angle at which you cut the end of a board to join it with another board at a corner. Unlike a butt joint where boards meet at 90 degrees, a miter joint creates a clean, seamless appearance by cutting both boards at complementary angles.

For a standard 90-degree corner, the miter angle is 45 degrees for each board. However, for corners that aren’t 90 degrees or when boards have different widths, the calculation becomes more complex and requires trigonometric formulas.

Miter joints are commonly used in:

  • Picture frames and mirrors
  • Door and window trim
  • Crown molding
  • Furniture making
  • Decorative woodworking projects

Miter Angle Formulas

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Equal Width Boards

For boards of equal width, the miter angle is simply half of the corner angle:

miter angle = corner angle ÷ 2

Example: For a 90° corner, each board is cut at 45°.

Unequal Width Boards

When boards have different widths, the miter angles are calculated using trigonometry:

miter angle A = arctan( (width B × sin(corner angle)) ÷ (width A + width B × cos(corner angle)) )
miter angle B = corner angle – miter angle A

These formulas ensure that the joint line bisects the corner angle, creating a perfect fit regardless of board width differences.

Crown Molding (Compound Cuts)

Crown molding requires both miter and bevel angles because it’s installed at an angle to both the wall and ceiling. The calculations are more complex:

miter angle = arctan( cos(spring angle) × tan(corner angle ÷ 2) )
bevel angle = arcsin( sin(spring angle) × sin(corner angle ÷ 2) )

The spring angle is the angle at which the molding sits against the wall (typically 38° or 45°).

How to Set Your Miter Saw

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1 Measure the Corner Angle

Use a protractor or angle finder to accurately measure the corner angle. For inside corners, this is typically 90°, but older homes often have corners that aren’t perfectly square.

2 Measure Board Widths

Measure the width of both boards that will form the joint. If they’re the same width, the calculation simplifies.

3 Calculate Miter Angles

Use our calculator above to determine the exact miter angles for both boards based on your measurements.

4 Set Your Miter Saw

Most miter saws are calibrated so that 0° represents a straight 90° cut. To cut at a specific miter angle, set the saw to the calculated angle. For example, a 45° miter cut requires setting the saw to 45°.

5 Make Test Cuts

Always make test cuts on scrap wood first to verify your settings. Minor adjustments are often needed due to saw calibration or blade deflection.

6 Cut Your Workpieces

Once satisfied with your test cuts, proceed to cut your actual workpieces. Remember the carpenter’s adage: “Measure twice, cut once.”

Troubleshooting Tips

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Common Miter Joint Problems and Solutions

Gaps at the Joint

If you’re seeing gaps where the miter joints meet:

  • Check your measurements: Even a small error in measuring the corner angle can result in noticeable gaps.
  • Verify saw calibration: Use a reliable square to check that your miter saw is properly calibrated.
  • Account for blade kerf: The thickness of the saw blade can affect the cut. Our calculator includes kerf compensation for precise results.
Uneven Joint Line

If the joint line doesn’t bisect the corner evenly:

  • Confirm board widths: Make sure you’ve entered the correct widths for both boards.
  • Check for parallel surfaces: Ensure both boards have parallel edges.
  • Verify corner angle: Re-measure the corner angle, especially for non-90° corners.
Crown Molding Not Lying Flat

For crown molding installations:

  • Confirm spring angle: Make sure you’re using the correct spring angle for your molding.
  • Check both miter and bevel settings: Crown molding requires both angles to be set correctly on a compound miter saw.
  • Test cut scrap first: Always practice on scrap pieces before cutting expensive molding.

Frequently Asked Questions

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What is a miter angle?
A miter angle is the angle at which you cut the end of a board to join it with another board at a corner. For a standard 90-degree corner, the miter angle is 45 degrees for each board.
How do I calculate miter angles for unequal width boards?
For boards of unequal widths, the miter angle formula is more complex. You need to use trigonometry: miter angle = arctan((width1 × sin(corner angle)) / (width2 + width1 × cos(corner angle))). Our calculator handles this automatically.
What’s the difference between inside and outside corners?
Inside corners are where two walls meet in a concave angle (like a room corner), while outside corners protrude outward. The miter angles are complementary – if an inside corner requires 45-degree cuts, the corresponding outside corner would require 135-degree cuts.
How do I set up my miter saw for crown molding?
Crown molding requires compound miter cuts. You need to set both the miter angle (horizontal rotation) and bevel angle (vertical tilt). Our calculator provides both values based on your corner angle and the spring angle of your crown molding.
What is blade kerf and should I compensate for it?
Blade kerf is the width of material removed by the saw blade. For precise joinery, you may need to compensate for kerf by slightly adjusting your cut positions. Our calculator includes an optional kerf compensation feature.
Why are my miter joints not fitting perfectly?
Common issues include inaccurate measuring, saw calibration problems, blade deflection, or wall irregularities. Always measure twice, make test cuts on scrap wood, and ensure your saw is properly calibrated.