Spindle RPM / SFM Calculator
Convert between spindle RPM and surface speed (SFM / m/min) for any cutter diameter.
Calculation Direction
Cutter Diameter
Common: 3mm, 6mm, 8mm, 10mm, 12mm
Cutting Speed
Result
Required RPM
-
rpm
Equivalent in other unit
-
Material Speed Reference
Click a row to use the carbide midpoint as cutting speed.
| Material | HSS (m/min) | Carbide (m/min) |
|---|
Frequently Asked Questions
What is SFM (Surface Feet per Minute)?
SFM stands for Surface Feet per Minute. It describes the speed at which the cutting edge of the tool moves across the surface of the workpiece. Every material has an optimal SFM range — too slow causes rubbing and heat buildup, while too fast wears the tool prematurely. SFM is the imperial equivalent of the metric cutting speed measured in meters per minute (m/min).
How do I choose the right cutting speed for my material?
Start with the material speed reference table above. Use the HSS values for high-speed steel end mills and the Carbide values for carbide tooling. Within each range, start at the lower end for harder alloys or deep cuts, and move toward the higher end for softer grades and light finishing passes. Always check your tool manufacturer's recommendations when available, as coatings (TiN, AlTiN, etc.) can increase recommended speeds significantly.
What if my calculated RPM exceeds my spindle's maximum?
If the required RPM is higher than your spindle can achieve, you have two options: use a larger diameter cutter (which lowers the required RPM for the same surface speed) or run at your spindle's maximum RPM and accept a lower-than-ideal surface speed. In the second case, reduce the feed rate proportionally to maintain the correct chip load. Small hobby CNC routers often run into this with very small diameter bits in soft materials like aluminum.