How to choose an inner tube:
Check all the information indicated on the sidewall of the tyre (diameter and width). For example, 14 x 1.90 means your tyre is 14 inches in diameter and 1.90 inches wide.
On the tyre sidewall you will also find the dimensions in mm in ETRTO international units. For example, 47-254 means a tyre that is 47mm wide and has an inner diameter of 254mm (approx. 14 x 1.90).