Wheel Size Speed Calculator

How it is calculated

Each turn of the wheel moves you forward by one circumference, so speed (km/h) = circumference (mm) ÷ 1,000,000 × RPM × 60. The division by 1,000,000 converts millimetres to kilometres, and the 60 converts minutes to hours. Miles per hour is the km/h value divided by 1.60934. Both results are shown with one decimal. The RPM field means wheel revolutions per minute, not pedal cadence; pedal cadence must first be multiplied by the gear ratio. The tool accepts an RPM of zero (0.0 km/h) but shows no result for a circumference outside 100–10,000 mm, or for an RPM that is negative or above 10,000. It assumes no slip and uses the circumference you type, so a wrong tyre value shifts every result.

Common mistakes

• Typing pedal cadence (for example 90) as the RPM. The field is wheel revolutions; at a 50 ÷ 16 gear, 90 pedal RPM is about 281 wheel RPM, which is 35.5 km/h on this wheel, not the 11.4 km/h that 90 would show.
• Entering the circumference in metres or centimetres. The field is in millimetres, and 2.105 is below the 100 mm minimum, so no result appears.
• Entering the wheel diameter (such as 700) instead of the circumference. A value of 700 is accepted as a 700 mm circumference and gives a speed far too low; multiply the diameter by π first (diameter 670 mm is a circumference of about 2,105 mm).
• Using the printed tyre size without checking the rolled value. Tyre width, pressure and rider weight change the real circumference by a few millimetres.