Machining · feeds speeds
Drill RPM Calculator
Calculate drill spindle RPM from cutting diameter and a user-sourced surface speed, with optional feed per revolution.
Browser calculator
Calculate drill RPM
Enter cutting diameter and a cutting-speed value from the exact drill source.
A geometry-only drill diameter example is preloaded. Enter cutting speed from the exact tool source; BrowserPowerTools supplies no starting speed.
Surface speed must be greater than zero.
How to calculate drill RPM
Choose metric or inch units, enter the drill’s cutting diameter, and enter a cutting-speed value from the exact drill manufacturer’s current information. Optional feed per revolution adds a calculated linear feed. A maximum RPM you enter creates a warning but never silently clamps the mathematical answer.
RPM = 1000 × m/min ÷ (π × diameter mm)
RPM = 12 × SFM ÷ (π × diameter in)
feed per minute = feed per revolution × RPM
Worked example
A 10 mm drill and a user-entered 30 m/min produce 954.93 RPM. If the user also enters 0.1 mm/rev, calculated feed is 95.493 mm/min.
These inputs demonstrate the equation; they are not a recommendation for a particular tool or work material.
Selecting defensible inputs
Confirm the exact drill type, cutting diameter, tool material/coating, work material and hardness, operation, coolant and setup. Indexable drills, step drills, annular cutters, deep holes and interrupted cuts can require product-specific definitions and limits. Use the cutter maker’s current data and the machine documentation.
Common mistakes
- Entering radius instead of diameter.
- Treating feed per tooth as drill feed per revolution.
- Copying an SFM value for a different tool material, coating or workpiece.
- Ignoring the machine’s spindle range, power, holder and workholding limits.
- Assuming calculated RPM is a safe recommendation.
FAQ
Why does a smaller drill produce higher RPM?
At a fixed surface speed, RPM is inversely proportional to diameter.
Does the tool round to a machine speed?
No. It shows the calculated relationship and warns against an optional user limit without making the operating decision.
Can I use a chart from another manufacturer?
Only if that source explicitly applies to the actual tool and application. BrowserPowerTools intentionally bundles no generalized speed chart.
References and further reading
These sources define or explain the calculation. Source editions and model limits are part of the result—not decorative citations.
- Formulas and definitions for milling — metric, Sandvik Coromant; accessed 2026-08-22. CHIP-C01
- Mill Speeds and Feeds Formulas — Inch, Haas Automation; accessed 2026-08-22. CHIP-C02
- NIST Guide to the SI, National Institute of Standards and Technology; accessed 2026-08-22. CHIP-C04