Angle Cut Calculator

Free Online Angle Cut Calculator

This angle cut calculator works out the exact miter angle, bevel angle, and cut length you need before you ever pick up a saw. It covers three situations: a single angled cut across one board, two pieces meeting at a corner, and a full compound cut for angled trim like crown molding. Type in your numbers and the calculator updates instantly, with a diagram that shows the cut and a step-by-step breakdown of the math behind it.

You don't need to remember any trigonometry to use it. Pick the mode that matches your project, enter the board width and angle (or the corner and spring angle for compound cuts), and read off the saw settings. It works the same whether you're cutting wood, metal, or plastic, since the geometry doesn't care what the material is.

What Is an Angle Cut?

An angle cut is any cut made across a piece of material at something other than a plain 90-degree crosscut. Three terms come up constantly in woodworking and metalwork, and they each mean something different:

• Miter cut — an angled cut across the face or width of a board, seen from above. Picture frame corners and baseboard corners are miter cuts.
• Bevel cut — an angled cut through the thickness of a board, tilting the blade instead of the workpiece. This changes the edge profile rather than the face length.
• Compound cut — a miter and a bevel combined in a single cut. This is what you need whenever the material itself sits at an angle, such as crown molding leaning against a wall and ceiling.

Angle Cut Formulas

All three modes in this calculator come down to right-triangle trigonometry. Here are the formulas it uses:

• Simple cut length = Board Width ÷ cos(Cut Angle)
• Simple cut offset (how far the cut travels along the board) = Board Width × tan(Cut Angle)
• Corner miter angle (each piece) = Corner Angle ÷ 2
• Corner cut length = Board Width ÷ cos(Miter Angle)
• Compound miter angle = atan( tan(Corner Angle ÷ 2) × sin(Spring Angle) )
• Compound bevel angle = asin( cos(Spring Angle) × sin(Corner Angle ÷ 2) )

How to Use This Calculator

Start by choosing the mode that fits your cut. For a single angled crosscut — like the end of a shelf bracket or a picture frame leg — use Simple Cut and enter the board width and the angle away from square. For two boards meeting at a corner, such as baseboard, fencing, or a segmented ring, use Corner / Joint Cut and enter the angle the joint turns through (90° for a normal square corner). Building a hexagon, octagon, or another regular shape instead? Fill in the number of sides and the calculator works out the corner angle for you.

For crown molding, coving, or any trim that leans against the wall at an angle, switch to Compound Cut. Enter the wall corner angle and the molding's spring angle, and the calculator returns both the miter setting and the bevel setting your saw needs — the same two numbers printed on the compound miter charts sold at hardware stores.

Worked Example: Simple Angle Cut

Say you're cutting the end of a 4-inch-wide board at a 30° angle. The cut length works out to 4 ÷ cos(30°) = 4 ÷ 0.866 = 4.62 inches — noticeably longer than the board itself, because the cut runs diagonally rather than straight across. The offset, or how far that cut travels along the length of the board, is 4 × tan(30°) = 2.31 inches. That's the measurement you'd mark before making the cut with a combination square or protractor.

Worked Example: Corner Joint Cut

For a standard square picture frame, the corner angle is 90°, so each of the four pieces is mitered at 90° ÷ 2 = 45°. Set both boards to 45° on the saw, cut, and the two 45° faces meet to form a clean 90° corner. On a 3-inch-wide frame piece, the cut face itself measures 3 ÷ cos(45°) = 4.24 inches — again longer than the board is wide, since the blade travels the diagonal.

Building something with more sides changes the numbers but not the method. A regular hexagon has six 60° corners, so each miter angle is 60° ÷ 2 = 30°. An octagon (eight sides) needs a 22.5° miter, and a twelve-sided shape needs 15°. Enter the number of sides in this calculator and it works the angle out automatically.

Worked Example: Compound Cut for Crown Molding

Crown molding is where most people first run into compound cuts, because the molding doesn't sit flat against the wall — it springs off it at an angle. For a standard 90° inside corner with 45°-spring crown molding, this calculator returns a 35.26° miter angle and a 30° bevel angle. Those two numbers happen to match the classic "30/35.3" settings printed on almost every compound miter saw's crown-molding chart.

Switch to 38°-spring crown molding on the same 90° corner, and the settings change to roughly a 31.62° miter and a 33.86° bevel — the other commonly published pair of numbers. The molding's spring angle has a real, calculable effect on both saw settings, which is exactly why compound cuts trip people up when they try to eyeball them.

Common Corner Angles and Their Miter Settings

A quick reference for corner and joint cuts, using Miter Angle = Corner Angle ÷ 2:

• 90° square corner (4 sides) → 45° miter on each piece
• 72° corner (5 sides, pentagon) → 36° miter
• 60° corner (6 sides, hexagon) → 30° miter
• 45° corner (8 sides, octagon) → 22.5° miter
• 36° corner (10 sides, decagon) → 18° miter
• 30° corner (12 sides) → 15° miter
• 120° outside corner (obtuse joint) → 60° miter
• 135° outside corner → 67.5° miter

Tips for Getting a Clean, Accurate Cut

The math gets you the angle. A few habits get you the fit:

• Always cut a test piece from scrap first and check the fit before cutting your finished material.
• Account for the saw's kerf — the small amount of material the blade removes — by measuring and marking on the waste side of your line, not the finished side.
• Double-check whether your saw reads angles from the 90° (square) position or from 0° (parallel to the fence); this calculator's angles are measured from square, which matches most miter saws.
• For compound cuts, set the bevel first, then the miter, then confirm both settings on the saw before cutting — most compound miter saws hold the bevel less securely once the miter is engaged.
• Clamp thin or narrow stock rather than holding it by hand; angled cuts put more sideways force on the blade than a plain crosscut.
• Sand or plane very lightly after cutting if the joint is a hair off — a small adjustment is easier to fix by hand than by recutting the whole piece.

Where Angle Cuts Are Used

Angle cuts show up across almost every trade that works with rigid materials:

• Picture frames, mirrors, and door and window casing, which all rely on clean 45° miters at each corner.
• Crown molding, cove molding, and other raked trim, which need full compound cuts to sit flush against both the wall and ceiling.
• Fencing and decking, where rail ends are often mitered to follow a corner or a change in direction.
• Roof framing and rafters, where birdsmouth and end cuts follow the roof pitch.
• Metal fabrication and pipe work, where angle iron, tubing, and conduit are mitered to form clean corner joints.
• Segmented woodturning and bowl-making, where staves are cut at precise angles so a ring of pieces closes into a perfect circle.

Common Mistakes to Avoid

Most bad-fitting joints trace back to one of a handful of avoidable mistakes:

• Mixing up the miter angle and the corner angle — remember the miter setting on the saw is half the corner angle, not the corner angle itself.
• Forgetting that outside corners (like the outer edge of a deck) and inside corners (like the inside of a room) use the same formula but can be easy to enter backwards.
• Skipping the bevel setting on a compound cut and only setting the miter, which leaves the joint gapping open on one face.
• Not accounting for blade kerf on tight, high-precision joints such as segmented rings or small picture frames.
• Measuring board width from the wrong edge after the material has already been trimmed once, which throws off every cut length that follows.