# Wheel speed and RPM calculator for robots

> Convert wheel RPM to robot speed and back: enter wheel diameter and RPM or target speed to get m/s, km/h and the RPM you need.

Canonical: https://roboticsengineering.in/wheel-speed-rpm-calculator/ | Published: 2026-11-03 | Updated: 2026-11-04

**Robot speed is wheel circumference times wheel turns per second.** Enter the wheel diameter and either the RPM or the speed you want.

Wheel diameter (mm)Wheel speed (RPM)Target speed (m/s)

From RPM: **–** m/s (– km/h)For the target speed, wheel RPM needed: **–**

Real speed is lower than this under load, and the tyre squashes a little, which changes the effective diameter.

## How it is calculated

Circumference = π × diameter. Speed in m/s = circumference in metres × RPM ÷ 60. Needed RPM = speed × 60 ÷ circumference. Multiply m/s by 3.6 for km/h.

## A worked example

A 65 mm wheel has a circumference of π × 0.065 = 0.204 m. At 150 RPM it moves 0.204 × 150 ÷ 60 = 0.511 m/s, about 1.84 km/h. To drive at 0.5 m/s you need 0.5 × 60 ÷ 0.204 = 147 RPM.

## Common mistakes

- Typing the radius where the diameter is asked for.
- Using motor RPM instead of wheel RPM. Divide by the gear ratio first.
- Ignoring that two-wheel robots turn by running the wheels at different speeds.

## Related

[gear train calculator](https://roboticsengineering.in/gear-train-calculator/), [battery runtime calculator](https://roboticsengineering.in/robot-battery-runtime-calculator/), [robot under ₹2,000](https://roboticsengineering.in/robot-under-2000-india/).

Last reviewed: November 2026. The calculator runs in your browser and sends nothing anywhere. Results are ideal-case figures; add margin before you order parts.

## Another worked example

A 100 mm wheel has a circumference of π × 0.1 = 0.3142 m. At 60 RPM it moves 0.3142 × 60 ÷ 60 = 0.314 m/s, which is 0.314 × 3.6 = 1.13 km/h. To drive at 0.3 m/s you need 0.3 × 60 ÷ 0.3142 = 57.3 RPM.

## Turning with two driven wheels

A differential-drive robot turns because its two wheels run at different speeds. If the distance between the wheel contact points (the track width) is b, the turning rate is (right speed − left speed) ÷ b in radians per second. With a track of 150 mm, a right wheel at 0.4 m/s and a left wheel at 0.2 m/s: 0.2 ÷ 0.15 = 1.333 rad/s, which is about 76 degrees per second. The robot’s forward speed is the average of the two wheels, 0.3 m/s.

## From motor to wheel

Motor datasheets list shaft RPM. If a gearbox sits between the motor and the wheel, divide the motor RPM by the gear ratio first. A motor at 3,000 RPM through a 30:1 gearbox gives a wheel at 100 RPM.

## Assumptions and limits

- No-load RPM is a maximum. Under load and at battery voltage that sags, the real speed is lower.
- Wheels slip, especially while accelerating. Use encoders if you need distance that is more accurate than a calculation.
- Soft tyres squash and change the effective rolling diameter. Measure it by rolling the wheel over a marked distance if it matters.

## Common mistakes

- Entering the diameter in centimetres into a millimetre field.
- Forgetting that a different wheel size changes both top speed and the torque available at the ground.