How to use the decoder
- Copy the size from the sidewall or from the tire placard in the driver's door jamb.
- Type it in full, service description included, and each part is explained on its own line.
- Each part shows what it means and its value in inches and millimeters.
P225/65R17 102H, part by part
| Part | Meaning | Value |
|---|---|---|
| P | Tire type. P is a P-metric passenger tire, LT light truck, ST special trailer and T temporary spare. No letter means a European (ISO) metric size. | Passenger |
| 225 | Section width, sidewall to sidewall, in millimeters | 8.86 in (225 mm) |
| 65 | Aspect ratio: sidewall height as a percentage of the width | 5.76 in (146.3 mm) of sidewall |
| R | Radial construction. D or B mean bias-ply, rare on cars today. | Radial |
| 17 | Rim diameter in inches | 17 in (431.8 mm) |
| 102 | Load index | 1,874 lb (850 kg) per tire |
| H | Speed rating | 130 mph (210 km/h) |
Put together: 17 × 25.4 + 2 × 146.25 = 724.3 mm, so the tire is about 28.52 in tall overall.
Other markings on the sidewall
- DOT code: DOT followed by plant and size codes and, at the end, four digits for the week and year of manufacture. 2523 means week 25 of 2023.
- UTQG grades, found on most passenger tires sold in the US: treadwear (a relative number, higher lasts longer), traction (AA, A, B or C) and temperature (A, B or C).
- M+S: a mud and snow tread design. The three-peak mountain snowflake symbol means the tire passed a snow traction test.
- XL or Reinforced: extra load construction, with a higher load index at a higher pressure.
- Max. load and max. pressure: the tire's limits, not the pressure to run. Use the pressure on the door placard.
Sizes in inches
Truck and off-road tires are often sized in inches. 33x12.50R17LT means about 33 in tall and 12.50 in wide, radial, for a 17 in rim, light truck construction. There is no aspect ratio to work out because the overall diameter is written directly.
Where to find your original size
In the US, FMVSS 110 requires a tire placard, usually on the driver's door jamb, with the original tire sizes, the recommended cold inflation pressures and the vehicle's maximum load of occupants and cargo. The owner's manual has the same data. If your vehicle uses different sizes front and rear, the placard lists both.
Age matters as much as tread. Many tire and vehicle makers recommend replacing tires after 6 to 10 years even when the tread looks fine. Check the DOT date on a used tire or a spare before you rely on it.
Questions
What do the numbers on a tire mean?
In 225/65R17 102H: 225 mm wide, sidewall 65% of the width, radial, 17 in rim, load index 102 (1,874 lb or 850 kg per tire) and speed rating H (130 mph or 210 km/h).
What does 65 mean in a tire size?
It is the aspect ratio: the sidewall is 65% as tall as the tire is wide. On a 225 mm tire that is 146.3 mm, or 5.76 in.
How do I know how old my tires are?
Find the last four digits of the DOT code on one sidewall: the first two are the week, the last two the year. 0424 is the fourth week of 2024.
What is the difference between P-metric and Euro-metric sizes?
Both use the same width, ratio and rim numbers. They follow different load standards, so the same size can carry a different load at the same pressure. Match the load index when you swap one for the other.