Openings & corners
An opening cut taken from the face overruns the corner on the hidden side. The overcut tells you the exact offset so the back face lands where you intend.
How far a circular blade cuts past your line
A 24-inch blade set 6 inches deep runs more than 10 inches past the line you marked, on each face of the slab. The bottom of the cut is shorter than the top, because the blade is round and only its lowest point sits at your depth. Overcut, also called run-out, blade overshoot, or cut extension, is the horizontal distance from your line to where the cut actually ends on the surface.
The idea · why the back of a cut runs long
Why the back of the cut runs past your line
Picture the blade as a circle dropped partway into the stone. The line you marked sits under the deepest point of the arc. As the rim climbs back toward the surface, it leans forward of that point, so by the time the cut reaches the top face it has already overshot. The same thing happens behind the mark.
This is why a plunge or a stopped cut on a countertop leaves the underside short while the top reads long, and why an opening cut taken from the face can nick a corner you meant to leave whole. Cutters call it run-out, blade overshoot, or cut extension. It matters most on finished slabs, pool coping, and any cut that stops short of an edge, where an extra inch of kerf shows in the daylight.
Finished slabs & coping
On finished slabs and pool coping, an extra inch of kerf shows in the daylight. Knowing the cut extension keeps run-out off the surfaces you mean to leave clean.
Stopped & relief cuts
Any cut that stops short of an edge leaves the underside cut past the line you can see. Mark the real run-out and stop short deliberately, not by guesswork.
The math · one closed-form equation
The formula, and the four letters in it
One closed-form equation drives every mode. R is the blade radius, half the diameter you read off the blade. D is the depth of cut, measured straight down. The term 2R − D is what remains of the diameter above your cut.
overcut = √(D · (2R − D))
D = depth of cut, measured straight down
R = blade radius = blade diameter ÷ 2
√ = square root
Worked: 24″ blade → R = 12. At D = 6,
overcut = √(6 · (24 − 6)) = √108 ≈ 10.39″ (10 3/8″).
R = blade radius = blade diameter ÷ 2
√ = square root
Worked: 24″ blade → R = 12. At D = 6,
overcut = √(6 · (24 − 6)) = √108 ≈ 10.39″ (10 3/8″).
We take blade diameter as the input, not radius, because that is the number stamped on the blade and the one a cutter already carries in their head. Every generic chord calculator asks for a radius or a central angle instead, which forces you to re-map the real problem before you can read an answer.
Worked example · see it & look it up
A 24″ blade, 6 inches deep, worked out
Take a 24-inch blade, so R is 12, cutting 6 inches deep: overcut = √(6 · (24 − 6)) = √108 ≈ 10.39 in. The tool rounds that to the nearest sixteenth and shows 10 3/8 in. Doubling the depth from 4 to 8 inches adds barely two inches of overcut. The curve flattens because the blade is already near its widest horizontal span by the time it is buried halfway. That is also why eyeballing fails at shallow depths, where the overshoot grows fastest per inch and your gut underestimates it.
Side profile · scaled to your numbers live
Overcut for a 24″ blade across cut depths
| Cut depth | Overcut, 24-in blade |
|---|---|
| 1 in | 4 13/16″ |
| 2 in | 6 5/8″ |
| 4 in | 8 15/16″ |
| 6 in | 10 3/8″ |
| 8 in | 11 5/16″ |
| 11 in | 11 15/16″ |
Bevel mode · read this once
Tilt the blade and the depth changes first
Bevel mode handles an angled cut. Enter the slab thickness and the tilt, and the real slant depth becomes D = T ÷ cos(θ), which feeds straight back into the same overcut formula. Tilt is measured from vertical: 0 degrees is straight down, and at 0 the bevel result collapses exactly to the forward number. A 6-inch slab cut at 45 degrees has a slant depth near 8.49 inches, pushing overcut on a 24-inch blade to about 11 1/2 in.
0° = straight down
The field is labelled “tilt from vertical” and drawn on the diagram on purpose.
0° → blade upright, collapses exactly to Forward mode.
Larger angle → deeper slant depth D = thickness ÷ cos(angle).
The easiest mistake is reading the angle from horizontal: do that and the slant depth is wrong from the first keystroke, so the picture is there to catch a bad mental model before the saw moves.
0° → blade upright, collapses exactly to Forward mode.
Larger angle → deeper slant depth D = thickness ÷ cos(angle).
The easiest mistake is reading the angle from horizontal: do that and the slant depth is wrong from the first keystroke, so the picture is there to catch a bad mental model before the saw moves.
Reverse mode · a job-site guardrail
Running it backward to protect a clearance
Sometimes the constraint is the overshoot, not the depth. You have a wall, a pipe, or a form you can't run past. Reverse mode takes the largest overcut you can tolerate and returns the deepest single-pass cut that stays inside it, using D = R − √(R² − O²). A 24-inch blade with a 10-inch overcut limit can go about 5 3/8 in deep before it crosses the line. That turns a geometry formula into a job-site guardrail, which is the one move no other blade calculator we found makes.
Assumptions · where the number stops
What the number assumes, and where it stops
Single-pass depth caps at the blade radius. Past D = R the blade is buried to its center and the cut can't finish in one pass, so the tool shows a warning instead of a figure. It flags any tilt beyond 85 degrees as unreliable, and it rejects a reverse overcut larger than the radius, which has no real solution.
The formula ignores kerf, the blade's own thickness, so true overshoot runs a hair wider than the number shown. That is deliberate. Keeping kerf out keeps the result conservative. Read the answer as the geometric run-out for a clean, sharp blade, then add your own margin for a worn rim or a wandering cut.
For the abrasive-blade safety limits that sit outside geometry, the governing reference is ANSI B7.1.
Questions · plain answers
Overcut, run-out, and the math, answered.
Overcut is the horizontal distance a round blade cuts past your marked line on the underside of the slab. Because the disc is round, at full plunge depth the rim exits past the marked line on the bottom face even though the blade only dropped straight down, so the cut on the bottom runs longer than the line you drew on top. Cutters also call it run-out, blade overshoot, or cut extension.
Now run your own numbers.
You know what overcut is and where it comes from. Punch in your blade and depth, get the real run-out in fractional inches, and mark it before you plunge.
Back to the calculator