Grinding wheel RPM calculator
Spindle speed for any wheel.
Enter the wheel diameter and the surface speed you want to get the RPM, plus the maximum RPM from the speed printed on the wheel. Free, no sign-up.
- Metric or imperialMillimetres and m/s, or inches and SFPM. Switching converts what you typed.
- Maximum RPM for your wheelFrom the label's maximum in m/s, SFPM or RPM, rounded down to stay safe.
- Maximum RPM charts belowFor 13 metric and 13 imperial wheel sizes.
The grinding wheel RPM formula.
RPM is the surface speed turned back into spindle turns. A smaller wheel needs more turns for the same speed.
Metric
ns = 60,000 × vs / (π × ds)
vs is the surface speed in m/s and ds the wheel diameter in millimetres.
Imperial
RPM = SFPM × 12 / (π × D)
D is the wheel diameter in inches.
Worked examples
A 400 mm wheel at 33 m/s needs 60,000 × 33 / (π × 400) = 1,576 RPM. If the wheel is rated 35 m/s, its maximum is 1,671 RPM. A 16 in wheel at 6,500 SFPM needs 1,552 RPM.
The RPM on the wheel comes first
When a wheel prints a maximum RPM, never exceed it, even after the wheel has worn smaller. The machine's spindle and guard must be rated for the speed too.
Maximum RPM by wheel diameter.
The highest RPM at which a wheel's edge stays at each speed rating. Values are rounded down.
| Wheel diameter | 35 m/s | 45 m/s | 50 m/s | 63 m/s | 80 m/s |
|---|---|---|---|---|---|
| 100 mm | 6,684 | 8,594 | 9,549 | 12,032 | 15,278 |
| 125 mm | 5,347 | 6,875 | 7,639 | 9,625 | 12,223 |
| 150 mm | 4,456 | 5,729 | 6,366 | 8,021 | 10,185 |
| 175 mm | 3,819 | 4,911 | 5,456 | 6,875 | 8,730 |
| 200 mm | 3,342 | 4,297 | 4,774 | 6,016 | 7,639 |
| 250 mm | 2,673 | 3,437 | 3,819 | 4,812 | 6,111 |
| 300 mm | 2,228 | 2,864 | 3,183 | 4,010 | 5,092 |
| 350 mm | 1,909 | 2,455 | 2,728 | 3,437 | 4,365 |
| 400 mm | 1,671 | 2,148 | 2,387 | 3,008 | 3,819 |
| 450 mm | 1,485 | 1,909 | 2,122 | 2,673 | 3,395 |
| 500 mm | 1,336 | 1,718 | 1,909 | 2,406 | 3,055 |
| 600 mm | 1,114 | 1,432 | 1,591 | 2,005 | 2,546 |
| 750 mm | 891 | 1,145 | 1,273 | 1,604 | 2,037 |
| Wheel diameter | 6,500 SFPM | 8,500 SFPM | 9,500 SFPM | 12,000 SFPM | 16,000 SFPM |
|---|---|---|---|---|---|
| 4 in | 6,207 | 8,116 | 9,071 | 11,459 | 15,278 |
| 5 in | 4,965 | 6,493 | 7,257 | 9,167 | 12,223 |
| 6 in | 4,138 | 5,411 | 6,047 | 7,639 | 10,185 |
| 7 in | 3,546 | 4,638 | 5,183 | 6,548 | 8,730 |
| 8 in | 3,103 | 4,058 | 4,535 | 5,729 | 7,639 |
| 10 in | 2,482 | 3,246 | 3,628 | 4,583 | 6,111 |
| 12 in | 2,069 | 2,705 | 3,023 | 3,819 | 5,092 |
| 14 in | 1,773 | 2,319 | 2,591 | 3,274 | 4,365 |
| 16 in | 1,551 | 2,029 | 2,267 | 2,864 | 3,819 |
| 18 in | 1,379 | 1,803 | 2,015 | 2,546 | 3,395 |
| 20 in | 1,241 | 1,623 | 1,814 | 2,291 | 3,055 |
| 24 in | 1,034 | 1,352 | 1,511 | 1,909 | 2,546 |
| 30 in | 827 | 1,082 | 1,209 | 1,527 | 2,037 |
These are the speeds at which a wheel of that diameter reaches each rating. If your wheel prints its own maximum RPM, that number takes priority.
Grinding wheel RPM questions.
Short answers to what machinists ask most.
How do I find the maximum RPM for a grinding wheel?
Read it on the wheel or its label: most wheels print a maximum RPM, a maximum surface speed, or both. If only the surface speed is printed, maximum RPM = 60,000 × maximum m/s / (π × diameter in mm). A 400 mm wheel rated 35 m/s may run at up to 1,671 RPM.
What is the difference between wheel RPM and machine RPM?
Machine RPM is the speed the spindle actually turns at. Wheel RPM is the maximum the wheel is rated for. The machine's speed must always be at or below the wheel's rating.
Can I raise the RPM as the wheel wears?
Yes, to keep the surface speed steady as the diameter shrinks, as long as you stay at or below the maximum RPM printed on the wheel and the machine's own rating.
Why does a smaller wheel need more RPM?
Its edge travels a shorter distance each turn. For the same surface speed, a 200 mm wheel needs twice the RPM of a 400 mm wheel.
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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