RPM to Linear Speed Calculator
Rotational speed alone doesn't tell you how fast a surface point is actually moving — that depends on the diameter too, which is why a small wheel and a large wheel spinning at the same RPM travel very different actual speeds.
Inputs
Result
15.708 m/s
56.55 km/h
How the rpm to linear speed calculator works
Surface (linear) speed = π × diameter × RPM ÷ 60, converting the diameter from mm to metres and RPM (per minute) to a per-second basis.
Worked example: 1,500 RPM, 200 mm diameter
- Diameter in metres: 200 ÷ 1,000 = 0.2 m.
- Speed = π × 0.2 × 1,500 ÷ 60 ≈ 15.71 m/s.
- In km/h: 15.71 × 3.6 ≈ 56.55 km/h.
Common mistakes to avoid
Assuming the same RPM always means the same surface speed
Surface speed scales directly with diameter — doubling the diameter at the same RPM exactly doubles the surface speed, which is why cutting-tool and tyre specifications always pair RPM with a specific diameter.
Entering diameter instead of radius, or vice versa, inconsistently with the formula
This formula specifically expects diameter (not radius) in millimetres — halving or doubling by using the wrong one throws the result off by exactly a factor of 2.
Frequently asked questions
Why does this matter for cutting tools or grinding wheels?
Manufacturers specify a maximum safe surface speed for a tool material — the same RPM that's safe for a small-diameter wheel could exceed the safe surface speed on a larger one.
How is this related to a vehicle's speed from wheel RPM?
The exact same formula: a wheel's rotational speed (RPM) combined with its diameter gives the vehicle's linear ground speed, which is essentially how a mechanical speedometer historically worked.
What if I know surface speed and need to find the required RPM?
Rearrange: RPM = (speed in m/s × 60) ÷ (π × diameter in metres).
Does this account for slip, like a tyre slipping on a road surface?
No — this is the ideal surface speed assuming no slip; a slipping wheel's actual ground speed would be less than this calculation predicts.
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