Your blade runs long. Know exactly how far.
A round blade cuts past your line on the bottom of the slab. On a 24″ blade at 6″ deep that overrun is more than 10 inches, a number most cutters guess. Overcut gives you the real figure in fractional inches, with a live side-profile so you can mark it before you plunge.
See the derivation, the angle convention, and the FAQ on the Learn page, or scan the overcut reference tables just below.
The calculator
Mark the overcut at the back end of the cut on the underside before you plunge. The blade always exits long.
Blade overcut reference: distance by diameter and depth, single-pass limits, and bevel charts
A 24-inch blade cutting 6 inches deep runs 10 3/8 inches past your line on each face. That number is large, it is not intuitive, and it shifts with both blade size and depth. The tables below are the values cutters reach for off the saw: overcut by diameter and depth, how deep a single pass can go before the blade buries to its center, what a tilt does to the figure, and how far back you can cut against a fixed clearance.
Overcut by blade diameter and cut depth
Horizontal run-out past the line, vertical cut, rounded to the nearest sixteenth. Blank cells (n/a) are depths the blade can't reach in one pass, where the depth exceeds the radius. At the exact limit, where the depth equals the radius, the overcut equals the radius.
| Cut depth | 12 in | 16 in | 20 in | 24 in | 30 in | 36 in |
|---|---|---|---|---|---|---|
| 1 in | 3 5/16 | 3 7/8 | 4 3/8 | 4 13/16 | 5 3/8 | 5 15/16 |
| 2 in | 4 1/2 | 5 5/16 | 6 | 6 5/8 | 7 1/2 | 8 1/4 |
| 4 in | 5 11/16 | 6 15/16 | 8 | 8 15/16 | 10 3/16 | 11 5/16 |
| 6 in | 6 | 7 3/4 | 9 3/16 | 10 3/8 | 12 | 13 7/16 |
| 8 in | n/a | 8 | 9 13/16 | 11 5/16 | 13 1/4 | 14 15/16 |
Column headers are blade diameters. The overshoot grows fastest in the first inch or two of depth and flattens after that, which is why the shallow cuts are the ones people misjudge.
Blade sizes, single-pass limits, and tilt
Single-pass depth tops out at the blade radius. Past that point the rim sits buried to its center and the cut needs a second pass. The overcut at that maximum depth always equals the radius.
| Blade diameter | Metric size | Max single-pass depth | Overcut at max depth |
|---|---|---|---|
| 12 in | ~300 mm | 6 in | 6 in |
| 14 in | ~350 mm | 7 in | 7 in |
| 16 in | ~400 mm | 8 in | 8 in |
| 18 in | ~450 mm | 9 in | 9 in |
| 20 in | ~500 mm | 10 in | 10 in |
| 24 in | ~600 mm | 12 in | 12 in |
| 30 in | ~750 mm | 15 in | 15 in |
| 36 in | ~900 mm | 18 in | 18 in |
Walk-behind and hand-held diamond saws cluster around 12 to 24 inches; the larger sizes are flat-saw and wall-saw territory. Metric blades sell in round millimeter sizes, so a "600 mm" blade is 23.6 inches, not a true 24.
A tilted cut deepens the slant the blade has to reach through. The slant depth is the slab thickness times the multiplier below, and that slant depth feeds the same overcut math. Tilt reads from vertical, where 0 degrees is straight down.
| Tilt from vertical | Slant-depth multiplier | Overcut, 6 in slab, 24 in blade |
|---|---|---|
| 0° | ×1.00 | 10 3/8 in |
| 15° | ×1.04 | 10 1/2 in |
| 30° | ×1.15 | 10 7/8 in |
| 45° | ×1.41 | 11 1/2 in |
| 60° | ×2.00 | 12 in |
Working the problem backward against a wall or form you can't overrun gives the deepest single pass that stays inside a clearance. For a 24-inch blade: a 4-inch overcut limit caps depth near 11/16 in, 6 inches caps near 1 5/8 in, 8 inches near 3 1/16 in, 10 inches near 5 3/8 in, and 11 inches near 7 3/16 in.
Related concepts
- Kerf:
- the blade's own thickness, ignored by the geometric figure. True overshoot runs a hair wider than the table value, so the number is the conservative floor.
- Chord and sagitta:
- the same geometry under math names. Overcut is half a chord; cut depth is the sagitta (chord height).
- Run-out and overshoot:
- trade names for the same distance, plus "cut extension" for the part that shows on a finished face.
- ANSI B7.1:
- the safety standard for abrasive and diamond blade use that governs the limits geometry can't, such as RPM ratings and guard requirements.
- Multi-pass cutting:
- how to clear depths past the radius, where the single-pass ceiling in the table no longer applies.