CalculatorsWheel Circumference Calculator
Wheel Circumference Calculator
GPS computers still want a wheel circumference when you use a speed sensor. This page estimates it from the bead seat plus twice the labelled tyre width, before the tyre squashes under you.
Inputs
Results
- Circumference
- 2130 mm
The Result is indicative and educational. It does not constitute a design, a technical opinion or medical advice and does not replace calculations or verification by a person with the appropriate qualifications and authorisations. Before purchase, installation or use in practice – in particular in electrical installations – the Result should be verified by a qualified specialist. Details: Terms of Service, point 4.
How the number is made
Circumference mm = π × (bead-seat diameter + 2 × tyre width). 700c and 29-inch share 622 mm. 650b, sold as 27.5-inch for MTB, is 584. A traditional 26-inch is 559. Example: 700×25 → π × 672 = 2111 mm; the Garmin wheel-size chart lists 2105.
Against the Garmin chart, 700c tyres from 20 to 47 mm land within 1%. Wide 26-inch MTB tyres read 1–3% long, because they stand lower than they are wide. A roll-out test on the garage floor (valve at the bottom, one revolution, measure) beats this estimate for a final sensor calibration.
Related calculators
- Cadence to Speed Calculator
Uses this circumference to turn a gear into km/h.
- Tire Pressure Calculator
A soft tyre shortens the real circumference slightly.
Questions
Why not the number printed on the tyre?
700×28c is a label. The computer wants millimetres of circumference, which changes with width, pressure and rim.
How do I measure it for real?
Sit on the bike, valve at the bottom, roll one revolution, mark the floor, measure. Use this calculator when you cannot do that yet.
Is this the millimetre figure a GPS unit wants?
Yes. Garmin and Wahoo ask for the distance one wheel turn covers, in millimetres, so this result stays in millimetres with imperial units too. A soft tyre under a rider rolls a little shorter than this unloaded figure.
Example products
Product links are Affiliate Links to Amazon websites. Using them does not cost you anything extra, and if you make a purchase we may receive a commission. Details: Terms of Service, point 5.
- Speed sensor
Enter this millimetre value if the computer asks for wheel size instead of a tyre label.
$30–$60