How to choose an inner tube
Check all the information indicated on the sidewall of the tyre (diameter and width). For example, 24 x 2.10 means your tyre is 24 inches in diameter and 2.10 inches wide.
On the tyre sidewall you will also find the dimensions in mm in ETRTO international units. For example, 50-507 means a tyre that is 50mm wide and has an inner diameter of 507mm (approx. 24 x 2.00).