Start with the sidewall
How to read your tire size
Read the numbers and letters on your tire, find the size recommended for your vehicle, and understand the difference between tire size formats.
Where to find the correct tire size
Look for the tire-information placard, usually on the driver’s door jamb, and the owner’s manual. The sidewall tells you what is installed today; it may not be the original or approved fitment. Some vehicles specify different front and rear sizes.
How to read 225/65R17 102H
225 is the tire’s width in millimeters. 65 means the sidewall height is 65% of that width: about 146 mm, not 65 mm. R means radial construction, and 17 is the wheel diameter in inches. After the size, 102 is the load index and H is the speed rating. Together, 102H is called the service description.
Tire size decoder
Read your tire’s sidewall.
Select a marking in this example to see what it means.
Example size: 225/65R17 102H
Marking 1 of 6
Width
225 is the approximate width in millimeters, measured from sidewall to sidewall.
P, LT, and flotation sizes
P at the start identifies a passenger-car sizing format; LT identifies light-truck tires. Some passenger sizes have no prefix. A size such as 35×12.50R20 gives approximate overall diameter and width in inches, followed by construction and wheel diameter. These are different sizing systems with different load and inflation requirements. Do not swap between them just because the numbers look similar.
Before you change sizes
Start with a size approved for your exact year, make, model, and trim. A different size can affect clearance, speedometer readings, and vehicle systems. Wheel width and load capacity matter too. Different front and rear sizes are called a staggered fitment. Have an installer verify any change, including the vehicle’s requirements for matching tire dimensions and wear on all-wheel-drive vehicles.
Your quick reference
| Marking | What it means | Example |
|---|---|---|
| 225 | Approximate width from sidewall to sidewall | 225 millimeters |
| 65 | Sidewall height as a percentage of width | 65% of 225 mm ≈ 146 mm |
| R | Construction | Radial |
| 17 | Wheel diameter | 17 inches |
| 102 | Load index | 102 = 850 kg / 1,874 lb under specified conditions |
| H | Speed rating | H = 130 mph / 210 km/h test rating, not a driving recommendation |
Common questions
Is 17 the height of the tire?
No. In 225/65R17, 17 is the diameter of the wheel in inches. Overall tire height also includes the sidewalls above and below the wheel.
How do I read 35×12.50R20?
This flotation format gives the nominal overall tire diameter (35 inches), width (12.50 inches), radial construction (R), and wheel diameter (20 inches). These are nominal dimensions; actual measurements vary by model.
Are two tires with the same size always interchangeable?
No. Load index, speed rating, construction, wheel requirements, and vehicle approvals still need to match. Check the complete specification, not just the size code.
Does 65 mean a 65 mm sidewall?
No. It is a percentage of width. For 225/65R17, multiply 225 by 0.65 to get an approximate sidewall height of 146 mm. The same aspect ratio on a wider tire gives a taller sidewall.
Remember
Size is only the starting point. Confirm the load index, speed rating, and approved wheel fitment too.
Sources & further reading
- Michelin: tire size and specification changes ↗ (opens in a new tab)
- Michelin: tire markings explained ↗ (opens in a new tab)
Use this guide to understand the terminology. Follow your vehicle’s owner’s manual, tire placard, and the tire manufacturer’s instructions for your exact application.