Bike wheel circumference calculator
Set the bike computer to a wheel circumference of 2,130 mm. The wheel is 678.0 mm across with the tire on, and before any allowance its circumference is 2,130 mm.
Result
Wheel circumference
mm
Wheel diameter with tire
mm
Circumference before the allowance
mm
Wheel turns per kilometer
Wheel turns per mile
How it works
A bike computer counts wheel turns, so it needs to know how far the bike rolls in one turn. That is the bike computer wheel size, the wheel circumference. You can read it from a bike tire circumference chart if your tire is listed, but charts cover a fixed set of sizes and do not agree with each other. This calculator gets the tire circumference from the ETRTO size on the sidewall instead: the wheel diameter with the tire is the rim diameter plus twice the tire width, and the circumference is that times pi. Use the result as the wheel size setting for a cycle computer, in millimeters or centimeters. A loaded tire rolls a little shorter, so you can take an allowance off; a measured roll-out is still the most exact figure.
Formula
wheel diameter = rim bead seat diameter + 2 × tire width. Circumference = π × diameter. With an allowance for the loaded tire, circumference = π × diameter × (1 − allowance). Wheel turns per kilometer = 1 000 000 mm ÷ circumference in mm.
Worked example
The calculator opens with this example; the result above is computed from it.
| Input | Value |
|---|---|
| Rim size | 622 = 700C, 29 inch |
| Tire width | 28 mm |
| Allowance for the loaded tire | 0 % |
| Wheel circumference | 2,130 mm |
| Wheel diameter with tire | 678.0 mm |
| Circumference before the allowance | 2,130 mm |
| Wheel turns per kilometer | 469.5 |
| Wheel turns per mile | 755.6 |
Common cases
| Case | Starting values | Wheel circumference | Wheel diameter with tire | Circumference before the allowance | Wheel turns per kilometer | Wheel turns per mile |
|---|---|---|---|---|---|---|
| Road bike tire | Tire width 28 mm; Allowance for the loaded tire 0 % | 2,130 mm | 678.0 mm | 2,130 mm | 469.5 | 755.6 |
| Road bike tire with the rider on | Tire width 28 mm; Allowance for the loaded tire 1 % | 2,109 mm | 678.0 mm | 2,130 mm | 474.2 | 763.2 |
| Gravel bike tire | Tire width 40 mm; Allowance for the loaded tire 0 % | 2,205 mm | 702.0 mm | 2,205 mm | 453.4 | 729.7 |
| Twenty-nine inch mountain bike tire | Tire width 60 mm; Allowance for the loaded tire 0 % | 2,331 mm | 742.0 mm | 2,331 mm | 429.0 | 690.4 |
| Twenty-seven and a half inch mountain bike tire | Tire width 60 mm; Allowance for the loaded tire 0 % | 2,212 mm | 704.0 mm | 2,212 mm | 452.1 | 727.7 |
| Twenty inch folding bike tire | Tire width 40 mm; Allowance for the loaded tire 0 % | 1,527 mm | 486.0 mm | 1,527 mm | 655.0 | 1,054.1 |
Questions and answers
What wheel size do I enter in my bike computer?
Enter the wheel circumference. For a road tire 28 mm wide the wheel is 678.0 mm across with the tire on, which makes a circumference of 2,130 mm.
Does my weight change the wheel circumference?
A little. A loaded tire flattens and rolls shorter. With an allowance of 1 %, a wheel of 2,130 mm becomes 2,109 mm. Measuring the roll-out with you on the bike gives the exact figure.
Assumptions and limits
- The formula treats the tire as tall as it is wide. Real tires differ, so the result is an estimate, usually within a percent or two.
- With no allowance the figure is for an unloaded wheel. Your weight and a lower pressure make the wheel roll shorter.
- For an exact setting, roll the bike one wheel turn with you on it and measure the distance on the floor.
- A chart from a computer maker may give a slightly different number for the same tire, because some rows were measured on one brand of tire.
The result is an estimate for planning, not professional advice.
Sources
- Sheldon Brown: cyclecomputer calibration (circumference from the ISO size, a worked example, and how far real tires differ)retrieved 2026-10-13
- Wikipedia: ISO 5775 (overall diameter is the rim diameter plus twice the section height; bead seat diameters)retrieved 2026-10-13
- CatEye: tire size chart and the roll-out methodretrieved 2026-10-13
- Polar: wheel size settings (measure the roll-out; chart values are advisory)retrieved 2026-10-13
Last updated:
Method in depth: Wheel circumference from the tire size
Cite this page: Crank Math, “Bike wheel circumference calculator”, https://crank-math.pages.dev/wheels/bike-wheel-circumference-calculator/ (updated 13 October 2026).
Found a mistake? Email handycalc.sites+crankmath@gmail.com.