Depth Per Pass Calculator
Splitting a cut into equal passes sounds trivial until the numbers stop dividing cleanly: take too much per pass and you snap a bit or overload the spindle, take too little and the job takes twice as long for no better finish. This calculator solves the pass-planning triangle in any direction, so you can start from the total depth, the pass count, or the depth per pass you trust, and get the third number instantly.
It is built for milling, turning, drilling, grinding, and CNC routing, anywhere material comes off in layers. Enter exactly two values, leave the third blank, and read the answer, including a note when the pass count has been rounded up to cover the full depth.
Fill in exactly two of the three fields and leave the one you want solved blank. Filling all three, or only one, returns a reminder instead of a wrong answer.
Quick Answer
Key takeaways
- Depth per pass is total depth divided by the number of passes, and this tool solves all three rearrangements of that one relationship, including the pass count most calculators never offer.
- The safe depth per pass is set by your tool, not by the arithmetic. A common CNC routing rule caps depth per pass at half the bit diameter, so a 1/4 inch bit stays at or under 0.125 inches per pass.
- Pass counts are rounded up to a whole number, so the full depth is always covered: 1.000 inch at 0.300 inches per pass returns 4 passes, not 3. At the entered depth per pass that cuts 1.200 inches in total, and the tool flags the overshoot in the result instead of hiding it.
- On a lathe, depth of cut is radial: the diameter falls by twice the depth per pass, so a diameter drop of 5 mm means 2.5 mm per pass on the radius.
- Quick Answer
- How to use this calculator: pick the blank field
- The formulas: one relationship, three directions
- Worked example: a 1.200 inch pocket in 4 passes
- Choosing a depth per pass your tool can actually survive
- The rounding trap when you solve for passes
- What competing calculators miss
- Frequently Asked Questions
- Add This Calculator to Your Website
- References
How to use this calculator: pick the blank field
The one habit this tool asks for is leaving exactly one field blank. The blank field is the question, and the two filled fields are the facts you already know.
Solve for depth per pass. You know the total depth and how many passes you want. Fill in total depth and number of passes, leave depth per pass blank. This is the everyday case: spreading a known cut over a chosen number of passes.
Solve for the number of passes. You know the total depth and the deepest pass your tool handles safely. Fill in total depth and depth per pass, leave the pass count blank. The answer is rounded up to a whole pass, so the full depth is always covered, and the result notes how far the entered depth per pass overshoots when the division is uneven.
Solve for total depth. You already have a pass plan and want the total it reaches. Fill in number of passes and depth per pass, leave total depth blank. Useful for checking a program before it runs, or for planning how deep a drilled hole needs to be alongside the fastener it must hold, which the bolt length calculator covers from the grip side.
Change one number and re-run. After a calculation the solved value fills its field, so clear the field you want to re-solve before calculating again, and keep exactly two fields filled each time.
The formulas: one relationship, three directions
Every answer this tool gives comes from a single identity: the passes, taken together, must add up to the total depth. Nothing else is assumed, which is why the same tool serves a mill, a lathe, a drill press, and a CNC router.
Two conventions are worth knowing before you trust the output. First, the fields are labelled in inches, and the result sentence says inches too. The division itself is unit-consistent, so machinists working in millimetres can enter millimetre values and the number returned is the correct millimetre answer, but read the number, not the unit word in the sentence: this tool has no unit switcher, and the word inches in its output does not convert anything. Second, a solved depth per pass is rounded to three decimals for display, so 1.000 inch over 3 passes shows as 0.333 inches per pass, and three passes at that displayed value total 0.999 inches. Program the unrounded value where your control allows it.
Worked example: a 1.200 inch pocket in 4 passes
The calculator is pre-filled with this case. A pocket 1.200 inches deep, roughed and finished in 4 equal passes, works out as follows, and the same three numbers solve in every direction.
| Direction | Inputs | Tool output |
|---|---|---|
| Depth per pass | 1.200 in total, 4 passes | 0.300 inches per pass |
| Number of passes | 1.200 in total, 0.300 in per pass | 4 passes |
| Total depth | 4 passes at 0.300 in | 1.200 inches |
| Pass | Depth removed this pass | Cumulative depth |
|---|---|---|
| 1 | 0.300 in | 0.300 in |
| 2 | 0.300 in | 0.600 in |
| 3 | 0.300 in | 0.900 in |
| 4 | 0.300 in | 1.200 in |
Equal passes are the right default for roughing, but many machinists deliberately make the last pass lighter: three passes at 0.350 inches reach 1.050 inches, leaving a 0.150 inch finishing pass that takes the pocket to size with a better surface. That split is a judgment the arithmetic cannot make for you, and it matters because the final pass is also where dimensional accuracy is won, the same accuracy that drawing tolerances and tools like the bonus tolerance calculator exist to protect. When you plan the job end to end, the cut length calculator handles the companion question of how much stock each part consumes.
Choosing a depth per pass your tool can actually survive
The calculator divides evenly. Whether the resulting number is safe depends on the tool diameter, the material, and the rigidity of the setup, and published guidance is consistent on the shape of the answer: smaller tools and harder materials mean shallower passes.
For CNC routing, Inventables, the maker of Easel, gives the clearest rule of thumb in its support documentation: keep depth per pass at or under half the bit diameter, so a 1/4 inch bit stays at 0.125 inches per pass and a 1/8 inch bit at 0.0625 inches. Run that through this tool and a 0.750 inch cut in plywood at 0.125 inches per pass needs exactly 6 passes. For end milling in metal, published axial depth of cut ranges scale with tool diameter in the same spirit:
| End mill diameter | Typical axial depth of cut range | Maximum axial depth of cut |
|---|---|---|
| 3 mm | 0.3 to 0.6 mm | 1.5 mm |
| 6 mm | 0.6 to 1.2 mm | 3 mm |
| 10 mm | 1 to 2 mm | 5 mm |
| 12 mm | 1.5 to 2.5 mm | 6 mm |
| 16 mm | 2 to 3.5 mm | 8 mm |
| 20 mm | 2.5 to 4 mm | 10 mm |
| 25 mm | 3 to 5 mm | 12 mm |
Sandvik Coromant frames the same limit from the tooling side: maximum cutting depth is primarily limited by insert size and machine power, with torque the binding constraint in roughing and vibration in finishing. Treat the table as a starting range for a rigid setup in typical materials, then solve for the pass count with a depth per pass inside it. Turning has one extra wrinkle: depth of cut there is measured on the radius, so turning a 65 mm diameter down to 60 mm is a 2.5 mm depth of cut per pass, not 5 mm, because the diameter falls by twice the radial depth.
Deeper passes: the case for
- Fewer passes means shorter cycle time and less total tool travel.
- Less rubbing at the cutting edge, which can work-harden some materials when passes are too light.
- Better chip formation on rigid machines with power to spare.
Deeper passes: the case against
- Higher cutting forces deflect the tool and the workpiece, costing accuracy.
- More heat and faster edge wear, and a snapped tool on the last pass scraps the part.
- Chatter and poor surface finish, especially on long, thin tools and light machines.
The rounding trap when you solve for passes
Pass counts have to be whole numbers, and this tool rounds the exact quotient up to the next whole pass. Rounding to the nearest pass can mean short: enter a total depth of 1.000 inch and a depth per pass of 0.300 inches and the exact answer is 3.33 passes, which nearest rounding would cut to 3 passes. Three passes at 0.300 inches cut only 0.900 inches, leaving 0.100 inches of material behind. This tool instead returns 4 passes, so the full depth is always covered.
What competing calculators miss
Most depth per pass calculators solve exactly one direction: total depth and passes in, depth per pass out. If you start from the other end, knowing the deepest pass your bit survives and needing the pass count, they leave you to do the division and the rounding judgment yourself, and none of them rounds the count up or warns you when a rounded count would fail to reach the full depth. One competitor adds a recommended maximum depth from tool diameter and material, which is a useful idea, but the recommendation is a single generic figure rather than the diameter-scaled ranges published in machining references, and it still cannot solve for total depth from a pass plan you already have.
This page keeps all three solving directions in one tool, shows the pass-by-pass schedule for the worked example, publishes the diameter-based depth ranges with their sources, and rounds the pass count up so the rounding trap cannot strand material, instead of presenting a rounded pass count as exact.
Frequently Asked Questions
Depth per pass is the thickness of material removed by a single pass of the tool. If a cut reaches 1.200 inches of total depth in 4 equal passes, each pass removes 0.300 inches. It applies to milling, turning, drilling, grinding, and CNC routing, anywhere the final depth is reached in layers rather than in one cut.
Divide the total depth by the depth per pass you plan to take. In this calculator, fill in total depth and depth per pass and leave the number of passes blank. The result is rounded up to a whole pass, so the full depth is always covered. Check the rounding note in the result for the overshoot at the entered depth per pass, and solve again for the slightly smaller depth per pass that divides evenly if you want equal passes.
Because the fields and the result sentence are labelled in inches and the tool has no unit switcher. The arithmetic is a plain division, so if you enter millimetre values consistently, the number returned is the correct millimetre answer. Only the unit word in the sentence is wrong for metric work, so trust the number and ignore the word, or convert your inputs to inches first.
A widely used CNC routing rule, published by Inventables for Easel, caps depth per pass at half the bit diameter. For a 1/4 inch bit that is 0.125 inches per pass, and for a 1/8 inch bit it is 0.0625 inches. A 0.750 inch deep cut at 0.125 inches per pass therefore needs 6 passes, which this calculator confirms when you solve for the pass count.
The solved depth per pass is shown to three decimal places, and the solved pass count is rounded up to the next whole pass. Rounding to the nearest pass could leave material behind, so this tool rounds up instead: 1.000 inch at 0.300 inches per pass solves to 4 passes, which cut 1.200 inches at the entered depth per pass. The result box flags that overshoot, and you can either make the last pass lighter or re-solve at the new count for a slightly smaller even depth per pass, 0.250 inches in that example.
They describe the same quantity from two angles. Depth of cut is the general machining term for how deep the tool engages, split into axial depth along the tool axis and radial depth across it in milling. Depth per pass is that same depth expressed as a plan: the share of the total depth assigned to one pass. On a lathe, remember the depth of cut is radial, so the diameter shrinks by twice the depth per pass.
Often, yes. Equal passes are efficient for roughing, but a lighter final pass reduces tool deflection and leaves a better surface at the final size. A common pattern is to rough most of the depth in equal passes and reserve roughly 0.100 to 0.150 inches of the example depth range for one finishing pass. This calculator splits evenly, so plan the finishing allowance by solving the roughing depth separately from the finish pass.
No. It divides the depth you give it and cannot see your tool, material, or machine. Safe values come from toolmaker guidance and references such as the diameter-based ranges in this article: smaller tools and harder materials need shallower passes, and maximum cutting depth is limited by insert size and machine power. Use those ranges to pick a depth per pass, then let the tool work out the pass count.
Add This Calculator to Your Website
References
- Sandvik Coromant, "Milling formulas and definitions" - the toolmaker reference defining axial cutting depth (ap) and radial cutting depth (ae), and noting that maximum cutting depth is limited primarily by insert size and machine power. Sandvik Coromant: Milling Formulas and Definitions. Accessed October 2026.
- Inventables, Easel Support, "Cut Depth and Depth Per Pass" - the CNC routing guidance behind the rule that depth per pass should not exceed half the bit diameter, with worked pass counts for common bits. Inventables Easel Support: Cut Depth and Depth Per Pass. Accessed October 2026.
- ProleanTech, "Thorough Guide On Depth Of Cutting In CNC Machining" - source of the end mill axial depth of cut ranges by tool diameter and the turning example in which a 65 mm to 60 mm diameter reduction is a 2.5 mm radial depth of cut. ProleanTech: Depth of Cutting in CNC Machining. Accessed October 2026.
- BraveCalculator, "Depth Per Pass Calculator" - a competing single-direction calculator checked for the competitor comparison in this article. BraveCalculator: Depth Per Pass Calculator. Accessed October 2026.
- Savvy Calculator, "Depth Per Pass Calculator" - a competing calculator checked for the competitor comparison, including its recommended maximum depth feature. Savvy Calculator: Depth Per Pass Calculator. Accessed October 2026.