How do you calculate a miter saw setting?
For the default 90° included corner, cut each member at 45° on a saw scale that reads 0° for a square crosscut. The change in direction is 90°. The two settings have equal magnitudes; their left or right orientation depends on the marked joint and stock face.
Included corner I + change in direction T = 180°.
Each saw miter setting M = (180° − I) / 2 = T / 2.
Blade bevel = 0° for this planar model.
The included angle is measured between rays extending from the joint along the two members. For an equal miter, the joint line bisects that angle. The cut line therefore makes half the included angle with each member, while a zero-based saw scale measures away from a perpendicular cut. Subtracting that half-angle from 90° gives the formula above.
A straight continuation has an included angle of 180°, a turn of 0° and two square-cut ends at 0°. This tool accepts included angles greater than 0° through 180°, or turns from 0° up to but not including 180°. Reflex corners, unequal-width flush joints and unequal miter splits need a different construction model.
Included angle versus turn angle: calculated examples
Choose the reference your measurement actually describes. A 135° included corner has a 45° turn and needs two 22.5° saw settings. Entering 135° as a turn describes a different joint. Changing the reference selector converts a valid entry to keep the same geometry.
| Included corner | Turn angle | Saw setting, each | Compared with an illustrative 45° travel limit |
|---|---|---|---|
| 180° | 0° | 0° | Within entered limit |
| 135° | 45° | 22.5° | Within entered limit |
| 120° | 60° | 30° | Within entered limit |
| 93° | 87° | 43.5° | Within entered limit |
| 90° | 90° | 45° | Within entered limit |
| 88° | 92° | 46° | Exceeds entered limit |
| 60° | 120° | 60° | Exceeds entered limit |
These are computed geometric examples, not measurements of completed joints. They do not establish an acceptable machining tolerance. A 93° included corner gives 43.5° per member, while an 88° corner gives 46°; simply halving the included angle would reverse the correction.
Check the scale and the actual saw range
The DEWALT DW708 manual defines its zero miter position as a blade perpendicular to the fence. It also describes a second scale that reads 90° at square, so the same physical cut can have a different number on a different scale. Use the zero-based setting shown here only with the matching reference on your saw.
Travel is model- and direction-specific. For example, that DW708 manual lists 50° left and 60° right; those values are not assigned to another saw. The calculator's 45° default is an editable comparison value. Enter the limit for the intended direction and compare both directions when your setup needs them. Being within the entered limit does not check stock width, thickness, fence clearance or a fixture.
For a flat miter, keep the blade bevel at 0° in this model. A compound cut changes both miter and bevel and requires additional geometry. This page does not supply compound crown-molding settings or a way to bypass machine stops. Verify the scale and joint orientation on scrap using the exact saw instructions.
Frequently asked questions
What is the formula for two equal miter cuts?
For an included corner angle I, each zero-based saw setting is (180° − I) / 2. If you know the change in direction T instead, each setting is T / 2. The two members share the same miter magnitude.
Why is a 135° corner cut at 22.5° instead of 67.5°?
The saw scale used here starts at 0° for a square crosscut. A 135° included corner changes direction by 45°, so each member needs a 22.5° miter. The 67.5° value is half the included corner, measured from a different reference.
What do included angle and change in direction mean?
The included angle is the non-reflex angle between two rays running from the joint out along the members. Change in direction is the amount a path turns as it passes through the joint: 180° minus the included angle. A straight continuation is 180° included and 0° turn.
Does this calculate compound bevels or crown-molding cuts?
No. This is a planar, equal-miter model with the blade bevel at 0°. Compound cuts need additional geometry such as a spring or slope angle. Unequal-width flush joints can also need unequal miters, which this tool does not calculate.
What if the result exceeds my saw’s miter range?
The tool flags a setting above the travel limit you enter. Check the correct left or right limit and stock capacity in your exact saw manual. A calculated angle within that number does not verify a cutting setup. Do not force the saw beyond its stops.
Sources and calculation scope
The source checks below support the scale convention and equal-miter conversion. The diagrams illustrate geometry and are not full-size cutting templates.
- DEWALT DW708 instruction manual — printed pp. 4, 7, 9 and 11: travel, square-cut zero, and miter scales
The manual defines square-cut zero and distinguishes its zero-based scale from its supplementary 90° scale. It gives model-specific travel and regular-frame examples. The general conversion here follows from the stated angle definitions.
- AltitudeCraft protractor manufacturer guide — corner angle to zero-based saw setting
The section about digital angle finders gives (180° − corner angle) / 2. Only the flat, equal-miter conversion is used here; the guide’s unrelated equipment claims are not adopted.
Plan stile-and-rail door parts with the Shaker door frame calculator, or arrange sheet panels with the plywood sheet layout tool. A miter angle does not replace the measured tongue and groove dimensions used for a cope-and-stick door frame.