CYCLE COMPUTER
TIRE SIZE CALCULATOR


To use the calculator below, select a wheel and tire size from the table or enter the wheel and tire size in mm in the "Dia. (mm)" boxes. It will automatically calculate the estimated circumference in mm (used by most new cycle computers), cm (used by some cycle computers).

 

Wheel Size
SizeDia. (mm)
Tire
SizeDia. (mm)
Estimated Wheel Circumference/Computer Setting
mmcm

 

The calculator above is based on the ISO/ETRTO (European Tyre and Rim Technical Organization) tire size which specifies tire size as a tire width and rim circumference in mm. A ISO tire size of 28-622 is how we would refer to a 700 x 28C tire has a tire width of 28 mm and a rim diameter of 622 mm.


INCHES TO MM CONVERTER


If your wheel size isn't listed in in the drop down above, you can just enter the number into the Dia. (mm) field. If you have inches and need mm, enter them in the following box:

Inchesmm

ROLLOUT TEST


Another way to set your wheel size without any calculations at all is to measure the distance you travel in one revolution of the tire with it inflated to the pressure you normally would use. This is easier said than done. Two suggested ways to do this are:

  1. Wall
    • Sit on your bike next to a wall.
    • Roll forward till your valve stem is at the bottom of the wheel.
    • Have a friend mark that spot with tape of chalk.
    • Roll forward one revolution of the wheel so the valve stem is at the bottom of the wheel again.
    • Mark that spot with tape of chalk.
    • Measure the distance between the two marks in mm. That's your number!
  2. Paint or Water
    • Put a blob of wet paint or water on the pavement.
    • Ride over it and keep riding.
    • Each time your tire hits the pavement again, it should leave a mark.
    • You should be able to measure the distance between marks (or between multiple marks for even greater accuracy).
    • Measure that distance in mm. That's your number!