Lathe RPM calculator
Pick your workpiece diameter, material, and tool type to get the right spindle speed for turning. Covers HSS and carbide tooling in metric and imperial.
Units
Tool material
Spindle limits
Recommended RPM
1,655rpm
RPM range
1,019–2,292 rpm
Cutting speed
80–180 m/min
Coolant / air blast
RecommendedFlood coolant or cutting oil recommended
G-code
S1655spindle speed, ready to paste into your program
RPM = Vc × 1000 / (π × D)
min: 80 m/min / (π × 25 mm) = 1,019 rpm
max: 180 m/min / (π × 25 mm) = 2,292 rpm
min: 80 m/min / (π × 25 mm) = 1,019 rpm
max: 180 m/min / (π × 25 mm) = 2,292 rpm
Lathe turning cutting speed reference
Typical cutting speeds for lathe turning with a sharp tool and adequate coolant where needed. These are starting points only. Actual speeds depend on your machine rigidity, depth of cut, tool condition, and coolant setup. Always start at the lower end of the range and increase while watching chip colour and tool wear.
| Material | HSS (m/min) | Carbide (m/min) | Coolant / air blast |
|---|---|---|---|
| Aluminium (6061 / free-cutting) | 60–120 | 200–500 | Recommended |
| Brass (free-cutting CZ121) | 60–120 | 200–400 | Not needed |
| Copper | 30–60 | 100–250 | Recommended |
| Mild steel (1018–1025) | 18–35 | 80–180 | Recommended |
| Carbon steel (1040–1050) | 12–25 | 60–150 | Recommended |
| Stainless steel (304) Work-hardening; use a rigid setup and a sharp insert | 8–18 | 45–100 | Required |
| Cast iron (gray) Brittle chip; cast-iron dust is harmful, use extraction | 12–25 | 60–130 | Not needed |
| Titanium (Ti6Al4V) Keep feed low and never let the tool dwell | 6–12 | 30–60 | Required |
| Hard plastic (nylon, acetal, ABS) Use a sharp tool. Liquid coolant can swell or craze the part | 100–250 | 250–500 | Not needed |
| Wood (hardwood) | 200–500 | 600–1500 | Not needed |
Frequently asked questions
How do I calculate lathe RPM?
Lathe RPM = (cutting speed × 1000) / (π × workpiece diameter) in metric, or (SFM × 12) / (π × diameter in inches) in imperial. Pick the cutting speed for your material and tool type, divide by the circumference of the workpiece, and you get the spindle speed that keeps the tool tip moving at the right surface speed.
What is cutting speed (Vc or SFM)?
Cutting speed is how fast the workpiece surface moves past the tool tip, measured in metres per minute (m/min) or surface feet per minute (SFM). Every material and tool combination has a recommended range. Too slow rubs and work-hardens the surface; too fast overheats the cutting edge and shortens tool life.
What is the difference between HSS and carbide tooling for turning?
High-speed steel (HSS) is tougher and cheaper but limited to lower cutting speeds. Carbide inserts are harder and heat-resistant, letting you run 3 to 5 times faster, though they chip more easily on interrupted cuts. Use HSS on soft materials, low-power lathes, or interrupted cuts; use carbide when you have the rigidity and power to take advantage of the higher speeds.
Why does workpiece diameter affect lathe RPM so much?
The tool tip travels a larger circumference on a bigger workpiece for every spindle revolution. To keep the cutting speed constant, the spindle must turn more slowly as diameter increases. A 100 mm bar needs less than half the RPM of a 40 mm bar to achieve the same surface speed.
What if the recommended RPM is higher than my lathe can reach?
Set your spindle maximum in the calculator and it will warn you when the recommendation exceeds it. You can still get good results by using the lower end of the cutting speed range, particularly with a sharp tool and the correct feed rate.
Does it matter whether I use metric or imperial units?
No. The calculator converts between m/min and SFM and between mm and inches, so the final RPM is the same either way. Use whichever units your machine and tooling datasheets are in.
RPM = (Vc × 1000) / (π × D); start at the low end of the range and increase while the chips are short and the tool stays cool.