CNC Feed Rate Calculator for Milling and Drilling
Compute feed rate from RPM and chip load (milling) or feed per revolution (drilling), in metric or imperial, with a reverse mode that recovers the chip load or feed/rev from a feed rate you are already running. Values are starting points — confirm against your tool maker's data.
Quick answer
This calculator computes CNC feed rate for both milling and drilling. Milling: Feed = RPM × flutes × chip load (mm/tooth or IPT). Drilling: Feed = RPM × feed per revolution (mm/rev or IPR). It also runs in reverse — given a feed rate, it returns the chip load or feed/rev so you can check a program you already run. The result is a starting point; the safe value comes from your tool manufacturer's recommendation and your setup.
01Feed rate calculator
Forward mode computes feed rate from chip load (milling) or feed
per revolution (drilling). Reverse mode recovers the per-edge value from a feed
rate you already run. All values are starting points — confirm against the
tool maker's data.
This tool is provided for reference purposes only. Users shall make their own assessment of actual circumstances, and no guarantee is made for absolute accuracy.
02Choose milling or drilling first
Milling mode
The tool has multiple flutes, so the feed rate is the per-tooth chip load multiplied by the number of flutes and the RPM. Use this for end mills, face mills and slot drills.
Drilling mode
The tool advances a fixed amount per revolution. There is no flute count to multiply — only RPM × feed per revolution. Use this for drills, reamers and taps.
03Milling formula
Forward
- Vf
- feed rate, mm/min or IPM
- z
- number of flutes
- fz
- chip load, mm/tooth or IPT
Reverse: fz = Vf / (RPM × z)
04Drilling formula
Forward
- Vf
- feed rate, mm/min or IPM
- fn
- feed per revolution, mm/rev or IPR
Reverse: fn = Vf / RPM
05Metric and imperial handling
| Quantity | Metric | Imperial |
|---|---|---|
| Feed rate | mm/min | IPM (inch/min) |
| Per-edge (milling) | mm/tooth | IPT (inch/tooth) |
| Per-rev (drilling) | mm/rev | IPR (inch/rev) |
Table 1. Unit pairs. The calculator switches all labels and the formula's units together, so you cannot accidentally mix systems mid-calculation.
06Worked examples
Check: same RPM ballpark, very different feeds — because the milling tool multiplies by four flutes and the drill does not. That contrast is exactly why the mode matters.
07Reverse calculation — auditing an existing program
Reverse mode answers "what chip load is this program actually running?" Take a feed rate you already use and recover the per-edge value:
- Milling: fz = Vf / (RPM × z). If the result is outside the tool maker's window, the program is wrong even if the part "looks fine".
- Drilling: fn = Vf / RPM. Compare to the recommended feed/rev for the drill grade and material.
08Adjustment guidance
If chips are dusty / edge rubbing
Effective chip load is too low. Raise feed/tooth (milling) or feed/rev (drilling); check for chip thinning on light radial passes; confirm the edge is sharp.
If edge chips / vibration
Effective chip load too high. Lower feed/tooth; shorten stick-out; add flutes to keep feed rate up; verify rigidity and power.
Adjust, then re-check against the tool maker's window and your first-article results. See the chip load guide for the full diagnosis order.
09Related tools and reading
FAQFrequently asked questions
Which formula should I use, milling or drilling?
It depends on the tool. Milling uses Feed = RPM × flutes × chip load per tooth, because an end mill has multiple edges. Drilling uses Feed = RPM × feed per revolution, because a drill advances a fixed amount per turn regardless of its two lips. Selecting the wrong mode is the most common feed-rate error — the calculator forces you to choose.
What is the difference between feed rate and feed per revolution?
Feed per revolution (mm/rev or IPR) is the advance per single turn. Feed rate (mm/min or IPM) is that advance multiplied by RPM — the speed the axis actually moves. Feed rate = RPM × feed/rev. They are related by spindle speed, not interchangeable.
What units will I get out?
Metric mode returns mm/min; imperial returns IPM (inches per minute). The per-edge value is mm/tooth (metric) or IPT (imperial). Pick the system your shop uses — the calculator shows the correct unit on every field.
Can it work backwards from a feed rate I already run?
Yes — switch to reverse mode. Give it the feed rate, RPM and flutes (milling) or just feed rate and RPM (drilling), and it returns the chip load or feed/rev. That is how you check whether an existing program is inside the tool's recommended window.
Why does drilling not use 'per tooth'?
A drill's two lips are not independent cutting edges the way end-mill flutes are; the drill is programmed as one advance per revolution. You can derive a per-lip bite (feed/rev ÷ 2) for diagnosis, but the control reads feed per revolution. Forcing a per-tooth model onto drilling is a frequent source of wrong numbers.
What if I enter zero flutes or a negative number?
The calculator blocks non-positive RPM and, in milling mode, flute counts below 1, and shows an inline error instead of a bad result. Zero flutes is physically impossible for milling.
Does the calculator recommend a chip load?
No. You supply the chip load or feed/rev; the calculator converts it to a feed rate. Where that input comes from is your tool manufacturer's data for the exact grade and material — our chip load guide explains how to read it.
Why do my chips look wrong even at the calculated feed?
Because chip load is not the only input. Radial engagement (chip thinning), tool sharpness, coolant and runout all shift the actual chip. If chips are dusty at the right feed, suspect chip thinning on a light radial pass and raise the feed accordingly.
Should feed rate change with depth?
Within a single tool pass, feed per revolution is usually held constant; what changes with depth is usually coolant and evacuation strategy (pecking). Very deep or interrupted holes may need a reduced breakthrough feed. Let the tool maker's window and the chip appearance guide you.
Are the calculated values guaranteed safe?
No. They are theoretical starting points. Real capability depends on rigidity, runout, coolant, material condition and hole depth. Start conservative, watch the chips, optimise and record.
●The CNC drilling & parameters library
Feed rate is the last of the four linked numbers. Pick the right mode first — milling and drilling use different formulas.
The complete hole-making framework: operations, drill types, accuracy, cycles and process selection.
How cutting speed, RPM, feed per revolution and chip load fit together, with starting points by material.
Built-up edge, long chips, burrs, deep holes and hole accuracy in 6061, 7075, 2024 and 5052.
Feed per tooth vs feed per revolution, chip thinning, and what chip shape tells you about your parameters.
What SFM and m/min measure, why diameter changes RPM, and how to convert between them correctly.
Convert surface speed and tool diameter into spindle RPM, in both imperial and metric units.
Canned cycle selection, Q/R/P/K parameters, G98/G99 returns, commented examples and alarms.
A decision framework from operation and material to geometry, coating, holder, reach and volume.
Flood, through-tool, MQL, air blast and dry machining, plus concentration, filtration and troubleshooting.
Identify flank wear, cratering, BUE, chipping and thermal cracking, then correct them in the right order.
Diameter, true position, cylindricity, finish, burrs, process capability and how each one is inspected.
Calculated values are starting points
A feed rate is only as good as the chip load behind it and the setup around it. Send us your application — tool model, material, depth, coolant and machine — and we will return a parameter set proven on a first article, not a number from a formula.
- 26 years of in-house precision machining
- Tooling, coolant and rigidity reviewed together
- 3-, 4- and 5-axis CNC, 100+ machines
- First-article proving before production
- ISO 9001 quality system
- 24-hour response on engineering reviews
