Find the tire size code on the sidewall
Read the format, such as 225/45R17
Measure the tire width from sidewall to sidewall
Measure the sidewall height from rim to tread edge
Measure the wheel diameter across the rim
Measure the overall tire diameter from top to bottom
Measure the tire circumference around the outside
Check the tire’s aspect ratio if listed
Compare all measurements to the size code
Use a tire size calculator if needed