RPM Calculator
Need to know how fast a wheel, gear, or spindle is turning? Enter any two of RPM, speed, and diameter to calculate the third. Works for vehicle tires, CNC spindles, pulleys, conveyor rollers, and anything else that spins.
The core formula:
RPM = Speed / Circumference, where Circumference = PI x Diameter
Once you know two of the three values (RPM, speed, diameter), you can solve for the third.
Common applications:
- Vehicle tires -- find engine RPM at highway speed for a given tire size
- Machining -- calculate spindle RPM for a cutter diameter and recommended surface speed
- Bicycles -- determine wheel RPM from riding speed and wheel size
- Conveyor systems -- calculate roller RPM for a target belt speed
- Pulleys and gears -- find output RPM from input RPM and diameter ratio
Surface speed (shown in ft/min and m/min) is critical in machining. Material data sheets specify recommended surface speeds for cutting tools, and you convert that to RPM based on your tool diameter.