Cutting Tools Reference Library · Wall Charts

SFM to RPM Chart

Spindle speed in RPM for common surface speeds and inch tool diameters, calculated from RPM = SFM × 3.82 ÷ diameter.

Ref CT-0056

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Surface feet per minute (SFM) is the speed of the cutting edge past the work. Tool and material makers give a recommended SFM; the machine needs RPM. The conversion is:

RPM = (SFM × 12) ÷ (π × D), which simplifies to RPM = SFM × 3.82 ÷ D
SFM = RPM × D × 0.262

D is the tool diameter in inches for drills, end mills and reamers, or the workpiece diameter for turning.

How to use it

Get the starting SFM for the tool material and work material from the tool maker. Find the tool diameter row and the nearest SFM column, then read the RPM. If the machine cannot reach that speed, run at its maximum and adjust feed.

RPM by diameter and surface speed

Diameter (in)	50 SFM	100 SFM	200 SFM	300 SFM	500 SFM	1,000 SFM
1/16	3,056	6,112	12,223	18,335	30,558	61,115
1/8	1,528	3,056	6,112	9,167	15,279	30,558
1/4	764	1,528	3,056	4,584	7,639	15,279
3/8	509	1,019	2,037	3,056	5,093	10,186
1/2	382	764	1,528	2,292	3,820	7,639
5/8	306	611	1,222	1,833	3,056	6,112
3/4	255	509	1,019	1,528	2,546	5,093
1	191	382	764	1,146	1,910	3,820
1-1/2	127	255	509	764	1,273	2,546
2	95	191	382	573	955	1,910

Key points

RPM scales directly with SFM and inversely with diameter. Double the diameter, halve the RPM.
Columns can be added: 150 SFM is the 50 SFM value plus the 100 SFM value.
These are calculated values, not recommendations. The right SFM depends on tool material, coating, work material, coolant and rigidity.
Feed is set separately: feed rate (IPM) = RPM × number of teeth × chip load, or RPM × IPR for drills.

Common mistakes

Using the shank diameter of a step or reduced-shank tool instead of the cutting diameter.
Using a carbide SFM with an HSS tool, which burns the tool quickly.
In turning, forgetting that the diameter, and so the surface speed, changes as the part gets smaller.

Governing standards: None. Starting speeds come from the tool manufacturer's data.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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