Measure the height of the tire from the top tread to the bottom tread.
Measure the width of the tire across the top tread.
Measure the rim size from rim to rim.
Place the numbers in order. For example, a 13-inch tire height with a 5-inch width that sits on a 6-inch rim will be written as "13 x 5 x 6" or "13/5 x 6." In some cases, tire measurements are recorded in millimeters. In that case, the tire size will be written as, "330 x 127- 6." The last number will always be recorded in inches, but depending on the brand of inner tube, both the height and width may be recorded in millimeters.
Take these measurements to any hardware store or lawn and garden shop. It will have an inner tube that will fit your needs.