Grinding wheel speed calculator
Surface speed in m/s and SFPM.
Enter the wheel diameter and the spindle speed to get the surface speed, then check it against the maximum printed on the wheel. Free, no sign-up.
- Metric or imperialMillimetres and m/s, or inches and SFPM. Switching converts what you typed.
- Checked against the wheelEnter the label's maximum in m/s, SFPM or RPM to see how close you are.
- Formula and example belowThe same calculation by hand, with a worked example.
The grinding wheel speed formula.
Surface speed is how fast the edge of the wheel travels. It depends on two things: the diameter and the RPM.
Metric, in metres per second
vs = π × ds × ns / 60,000
ds is the wheel diameter in millimetres and ns the spindle speed in RPM. Dividing by 60,000 turns millimetres per minute into metres per second.
Imperial, in surface feet per minute
SFPM = π × D × RPM / 12
D is the wheel diameter in inches. To convert between the two, 1 m/s = 196.85 SFPM.
Worked example
A 400 mm wheel at 1,500 RPM: π × 400 × 1,500 / 60,000 = 31.4 m/s, or 6,184 SFPM. On a wheel rated 35 m/s, that is 90% of its maximum.
As the wheel wears
Surface speed falls with the diameter. Dressed down to 350 mm, the same wheel runs at 27.5 m/s at 1,500 RPM, 12.5% slower. You can raise the RPM to win it back, but never above the RPM printed on the wheel.
Surface speed conversion table.
Common wheel speeds in m/s and SFPM, with the RPM each one needs on three wheel sizes.
| Surface speed | SFPM | RPM, 300 mm wheel | RPM, 400 mm wheel | RPM, 500 mm wheel |
|---|---|---|---|---|
| 20 m/s | 3,937 | 1,273 | 955 | 764 |
| 25 m/s | 4,921 | 1,592 | 1,194 | 955 |
| 30 m/s | 5,906 | 1,910 | 1,432 | 1,146 |
| 33 m/s | 6,496 | 2,101 | 1,576 | 1,261 |
| 35 m/s | 6,890 | 2,228 | 1,671 | 1,337 |
| 40 m/s | 7,874 | 2,546 | 1,910 | 1,528 |
| 45 m/s | 8,858 | 2,865 | 2,149 | 1,719 |
| 50 m/s | 9,843 | 3,183 | 2,387 | 1,910 |
| 60 m/s | 11,811 | 3,820 | 2,865 | 2,292 |
| 63 m/s | 12,402 | 4,011 | 3,008 | 2,406 |
| 80 m/s | 15,748 | 5,093 | 3,820 | 3,056 |
RPM values are rounded. The maximum speed printed on your wheel always takes priority.
Grinding wheel speed questions.
Short answers to what machinists ask most.
What is a normal grinding wheel speed?
Most conventional vitrified wheels run at 25 to 35 m/s, about 4,900 to 6,900 SFPM. Wheels built for higher speeds are marked 45, 50 or 63 m/s, and some superabrasive wheels go higher still. Internal grinding often runs slower because the wheels are small. Whatever the process, the limit is the maximum printed on the wheel or its label.
How do I convert m/s to SFPM?
Multiply by 196.85. To go from SFPM to m/s, divide by 196.85. For example, 35 m/s is about 6,890 SFPM.
Is surface speed the same as RPM?
No. RPM is how fast the spindle turns. Surface speed is how fast the edge of the wheel moves, so it also depends on the diameter. A 200 mm wheel at 3,000 RPM and a 400 mm wheel at 1,500 RPM both run at 31.4 m/s.
What happens if a wheel runs above its maximum speed?
It can burst. The maximum printed on the wheel is a safety limit, not a target. Never exceed it, never run the wheel above the RPM marked on it, and check that the machine and its guard are rated for the speed too.
Does this calculator save what I type?
No. It runs in your browser, and nothing you type is sent or stored.
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