What is a compound miter cut?

A compound miter cut combines two angled cuts on one workpiece: a miter (horizontal angle) and a bevel (blade tilt). Simple miter cuts change only the horizontal angle while keeping the blade vertical. Compound cuts are required when the workpiece is tilted relative to the wall surface, as with crown molding, or when joining pieces that meet at both a horizontal and vertical angle simultaneously.

What angle do I set my miter saw for a 90-degree corner?

Set your miter saw to 45° for a standard 90° corner. The miter angle formula is (180° − corner angle) / 2, so a 90° corner gives (180 − 90) / 2 = 45°. This applies to baseboards, door casing, chair rail, and any flat trim meeting at a square corner. If the corner is not exactly 90°, measure it with a digital angle finder and recalculate.

How do you calculate crown molding angles?

Crown molding requires compound miter angles calculated from two inputs: the wall corner angle and the crown's spring angle. The flat-on-saw formulas are: miter = arctan(sin(spring) / tan(corner/2)) and bevel = arcsin(cos(spring) × sin(corner/2)). For a standard 90° corner with 38° spring crown, the flat settings are 31.6° miter and 33.9° bevel. Alternatively, hold the crown nested at its spring angle against the saw fence and cut a simple 45° miter with no bevel.

What is a spring angle on crown molding?

The spring angle is the angle between the back of the crown molding and the wall when the crown is installed. Standard crown profiles come in two common spring angles: 38° (also called 52/38, where the crown tilts 52° from the ceiling and 38° from the wall) and 45° (also called 45/45, where both angles are equal). To find the spring angle on existing crown, hold a piece against the wall and ceiling, then measure the angle between the back and the wall with a protractor.

What is the difference between miter and bevel on a miter saw?

The miter is the horizontal rotation of the saw blade relative to the fence, controlled by the turntable at the base. The bevel is the vertical tilt of the blade relative to the table, controlled by the tilt mechanism on the saw head. A simple miter rotates the turntable while keeping the blade vertical (0° bevel). A compound cut adjusts both the miter turntable and the bevel tilt simultaneously.

How do you cut crown molding flat on a miter saw?

To cut crown flat, lay the crown face-up on the saw table and set both the miter and bevel angles from the compound miter formula. For 90° corners with 38° spring crown, set the miter to 31.6° and the bevel to 33.9°. For 45° spring crown at 90° corners, set 35.3° miter and 30° bevel. The flat method is preferred for sliding miter saws because the workpiece lies stable on the table, producing cleaner cuts on wide crown profiles.

What are the miter angles for an octagon?

Each joint in a regular octagon requires a 22.5° miter angle. The formula is 180° / number of sides, so 180° / 8 = 22.5°. The interior angle of a regular octagon is 135°. For other polygons: hexagon = 30°, pentagon = 36°, square = 45°, triangle = 60°, dodecagon = 15°. Multiply the miter angle by 2 to verify: the exterior angle at each joint should equal 360° / number of sides.

Free Compound Miter Calculator — Miter & Bevel Angles

How to Use the Compound Miter Calculator

How to Calculate Miter Angles

The miter angle for any corner joint is calculated with a simple formula:miter = (180° − corner angle) / 2. This works because a miter joint splits the difference between two meeting surfaces equally. For the most common case — a standard 90° corner — the miter angle is (180° − 90°) / 2 = 45°. Set your miter saw to 45° on either side for inside or outside corners, and the two pieces will meet at a clean right angle.

Not all corners are exactly 90°, however. Older homes may have walls that meet at 87° or 93°, and bay windows often create 135° or 150° corners. For a 135° corner, the miter angle is (180° − 135°) / 2 = 22.5°. This calculator handles any corner angle — simply enter the measured angle and read the precise miter setting directly, eliminating the mental math and reducing the chance of a mis-cut.

Understanding Compound Miter Cuts

A simple miter rotates the saw blade horizontally while keeping it perpendicular to the table. This is all you need when the workpiece lies flat against the wall — baseboards, door casing, chair rail, and picture frames all use simple miters. A compound miter adds a second angle: the saw blade also tilts (bevels) away from vertical. The combination of horizontal miter rotation and vertical bevel tilt produces a cut that matches joints where the workpiece is tilted relative to the wall surface.

The most common application for compound miter cuts is crown molding. Because crown molding bridges the wall and ceiling at an angle (the spring angle), a simple miter alone won't produce the correct joint geometry. You have two options: cut the crown flat on the saw table using compound miter and bevel settings, or hold the crown at its spring angle against the saw fence (the "nested" or "on-the-stick" method) and use a simple miter only. Both methods produce the same joint — the choice depends on your saw capacity and personal preference.

Crown Molding Spring Angle Explained

The spring angle is the angle between the back of the crown molding and the wall when the crown is installed in position. It determines how far the crown projects from the wall onto the ceiling. Two standard spring angles dominate the market:

38° (52/38 profile) — the most common spring angle, found on the majority of residential crown molding. The crown tilts 52° from the ceiling and 38° from the wall. For a 90° corner, the flat-on-saw compound settings are approximately 31.6° miter and 33.9° bevel.

45° (45/45 profile) — an equal-angle profile where the crown sits at the same angle to both the wall and the ceiling. For a 90° corner, the flat compound settings are approximately 35.3° miter and 30° bevel. The 45° spring angle is often found on larger, more ornate crown profiles.

To determine the spring angle of existing crown, hold a short piece against the wall and ceiling in its installed position. Place a protractor or digital angle finder between the back of the crown and the wall surface — that reading is the spring angle. Getting this measurement right is critical, because even a 2° error in spring angle will produce visibly open joints at every corner.

Flat vs Nested Cutting Methods

The flat method lays the crown face-up on the saw table. You then set both the miter angle (turntable rotation) and the bevel angle (blade tilt) according to the compound formulas. This method works well on sliding compound miter saws because the workpiece lies stable on the table, producing cleaner cuts — especially on wide crown profiles that might wobble if held at an angle. The flat method requires a saw capable of both miter and bevel adjustments simultaneously.

The nested method (also called "on-the-stick") holds the crown upside down and at its spring angle against the saw fence. In this position, the fence represents the ceiling and the table represents the wall. Because the workpiece is already tilted to its installed angle, only a simple miter cut is needed — no bevel at all. This method is conceptually simpler and avoids the need to look up compound angle charts. The trade-off is that you must hold the crown firmly at the correct angle throughout the cut, and your saw's fence height and crown capacity limit the size of molding you can cut this way.

Polygon Miter Joints

When building multi-sided shapes — picture frames, planters, columns, or gazebos — each joint requires a miter angle based on the number of sides. The formula is:miter angle = 180° / n, where n is the number of sides. The interior angle of a regular polygon is (n − 2) × 180° / n.

Common applications: a square (4 sides) needs 45° miters, ahexagonal planter (6 sides) needs 30° miters, and anoctagonal gazebo (8 sides) needs 22.5° miters. For apentagon (5 sides), each miter is 36°; for adodecagon (12 sides), each miter is 15°. This calculator computes the miter angle for any polygon from 3 to 24 sides, so you can tackle everything from triangular shelf brackets to complex multi-sided deck planters.

Pro Tips

Always test cuts on scrap material before cutting finish pieces. Crown molding and hardwood trim are expensive — a test joint costs only a few inches of offcut material and can save you from ruining a full-length piece.
Use a digital angle finder to verify wall corners — most "90°" corners are actually 87°–93°. Even a 1° deviation from 90° changes the optimal miter setting and will produce a visible gap at the joint.
For inside crown molding corners, many carpenters prefer coping over mitering for a tighter fit. A coped joint cuts the profile shape on one piece so it butts against the face of the adjoining piece, accommodating slight angle variations better than a miter.
Check that your miter saw blade is square to the fence and table before making compound cuts. A blade that is even 0.5° out of alignment will compound the error across both the miter and bevel angles, making accurate joints impossible.
Mark "left" and "right" on crown pieces before cutting — compound cuts are mirror images. An inside left corner uses the opposite miter and bevel direction from an inside right corner, and confusing the two is the most common crown molding mistake.