How to read a tire size
The code on the sidewall — for example P225/65R17 102H — packs seven pieces of information. Here is what each one means and what it tells you about the tire's real dimensions.
Last reviewed October 2, 2026
| Part | Meaning | For this tire |
|---|---|---|
| P | Service type: P = passenger, LT = light truck, ST = special trailer, T = temporary spare. No letter = Euro-metric. | Passenger tire |
| 225 | Section width in millimeters | 225 mm = 8.86 in |
| 65 | Aspect ratio: sidewall height as a % of the width | 65% × 225 = 146.3 mm = 5.76 in |
| R | Construction (R = radial) | Radial |
| 17 | Wheel (rim) diameter in inches | Fits a 17-inch wheel |
| 102 | Load index — maximum load per tire (see chart) | 850 kg / 1874 lb per tire |
| H | Speed symbol — maximum tested speed (see chart) | 210 km/h (130 mph) |
Put together, the overall diameter is the wheel plus two sidewalls: 17 + 2 × 5.76 = 28.52 in (724 mm). Try any size in the tire size calculator.
Inch (flotation) sizes
Off-road and light-truck tires are often labeled in inches: LT35x12.50R17 121Q means 35 in overall diameter, 12.50 in section width, radial, for a 17-inch wheel, load index 121 and speed symbol Q (160 km/h, 99 mph). The sidewall is (35 − 17) ÷ 2 = 9 in. Convert to metric with the inch ↔ metric converter.
Other markings you will see
- DOT code — ends with the week and year of manufacture (decode it).
- Load range (C, D, E, F) — on LT tires, the ply-rating equivalent; higher letters carry more load at higher pressure.
- XL / Reinforced — extra-load passenger tire.
- M+S — mud and snow tread geometry; 3PMSF (three-peak mountain snowflake) — meets a standardized snow traction test.
- UTQG (treadwear, traction, temperature) — US grading for passenger tires; treadwear grades are assigned by each manufacturer, so treadwear comparisons across brands are less reliable.
- Max. load / max. press. — the tire's limits, not the recommended pressure. Use the pressure on your vehicle placard.
Frequently asked questions
What does the R mean in a tire size?
Radial construction — the cord plies run radially across the tire. Almost all modern car and light-truck tires are radial. "D" or "-" means bias-ply and "B" belted bias; "ZR" in the size indicates a tire rated above 240 km/h (149 mph).
Is the first number the tread width?
No. It is the section width in millimeters — sidewall to sidewall at the widest point on the measuring rim. Tread width is narrower and varies by model.
What is the difference between P and LT tires?
P-metric tires are designed for passenger vehicles. LT (light truck) tires are built for heavier loads and are often run at higher pressures; their load capacity is also expressed as a load range (C, D, E…). Load capacity and correct pressures differ between the two, so a change from one type to the other should be checked with the vehicle documentation and a qualified tire professional.
What does XL mean?
Extra Load (also "Reinforced"): a passenger tire built to carry more load at a higher inflation pressure than a standard-load tire of the same size.
Related tools
- Tire size calculator
Diameter, width, sidewall and revolutions for any size.
- Load index chart
Every load index from 60 to 150 in kg and lb.
- Speed rating chart
Speed symbols J to Y in km/h and mph.
- DOT date code decoder
Find out when a tire was made and how old it is.