Tire Size Calculator
To use the calculator, 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).
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.
If your wheel size isn't listed in the drop down, you can just enter the number into the Dia. (mm) field.