How to Read a Tire Size
A tire size such as 225/45R17 94W reads: 225 mm section width, sidewall 45% of the width, R for radial construction, a 17-inch rim, load index 94 (670 kg per tire) and speed symbol W (270 km/h). The first four parts set the dimensions; the last two are the load and speed ratings.
Decode a tire size
The calculator needs JavaScript. The formulas and tables on this page work without it: sidewall = width × aspect ratio ÷ 100, and diameter = rim × 25.4 + 2 × sidewall (in mm).
Overall diameter
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The sidewall code, part by part
- 225: section width
- The width of the tire in millimetres at its widest point, measured on its measuring rim, not counting raised lettering.
- 45: aspect ratio
- The sidewall height as a percentage of the width: 45% of 225 mm is 101 mm.
- R: construction
- R means radial, which almost all car tires are. ZR appears on some high-speed tires. B and D mark bias and diagonal constructions. A dash means the construction is not given in the size.
- 17: rim diameter
- The diameter of the wheel the tire fits, in inches.
- 94: load index
- A code for the maximum load per tire at the reference pressure: 94 means 670 kg. See the table below.
- W: speed symbol
- A code for the maximum speed at which the tire can carry its load under the conditions of the standard: W means 270 km/h. See the table below.
- Prefixes and extra marks
- P in front (P225/45R17) marks a passenger tire sized to the US TRA standard; LT marks a light truck tire. XL or Extra Load and RF (reinforced) mark tires built for a higher load at a higher pressure.
Load index table
| Index | Load | Index | Load | Index | Load |
|---|---|---|---|---|---|
| 60 | 250 kg / 551 lb | 83 | 487 kg / 1074 lb | 106 | 950 kg / 2094 lb |
| 61 | 257 kg / 567 lb | 84 | 500 kg / 1102 lb | 107 | 975 kg / 2150 lb |
| 62 | 265 kg / 584 lb | 85 | 515 kg / 1135 lb | 108 | 1000 kg / 2205 lb |
| 63 | 272 kg / 600 lb | 86 | 530 kg / 1168 lb | 109 | 1030 kg / 2271 lb |
| 64 | 280 kg / 617 lb | 87 | 545 kg / 1202 lb | 110 | 1060 kg / 2337 lb |
| 65 | 290 kg / 639 lb | 88 | 560 kg / 1235 lb | 111 | 1090 kg / 2403 lb |
| 66 | 300 kg / 661 lb | 89 | 580 kg / 1279 lb | 112 | 1120 kg / 2469 lb |
| 67 | 307 kg / 677 lb | 90 | 600 kg / 1323 lb | 113 | 1150 kg / 2535 lb |
| 68 | 315 kg / 694 lb | 91 | 615 kg / 1356 lb | 114 | 1180 kg / 2601 lb |
| 69 | 325 kg / 717 lb | 92 | 630 kg / 1389 lb | 115 | 1215 kg / 2679 lb |
| 70 | 335 kg / 739 lb | 93 | 650 kg / 1433 lb | 116 | 1250 kg / 2756 lb |
| 71 | 345 kg / 761 lb | 94 | 670 kg / 1477 lb | 117 | 1285 kg / 2833 lb |
| 72 | 355 kg / 783 lb | 95 | 690 kg / 1521 lb | 118 | 1320 kg / 2910 lb |
| 73 | 365 kg / 805 lb | 96 | 710 kg / 1565 lb | 119 | 1360 kg / 2998 lb |
| 74 | 375 kg / 827 lb | 97 | 730 kg / 1609 lb | 120 | 1400 kg / 3086 lb |
| 75 | 387 kg / 853 lb | 98 | 750 kg / 1653 lb | 121 | 1450 kg / 3197 lb |
| 76 | 400 kg / 882 lb | 99 | 775 kg / 1709 lb | 122 | 1500 kg / 3307 lb |
| 77 | 412 kg / 908 lb | 100 | 800 kg / 1764 lb | 123 | 1550 kg / 3417 lb |
| 78 | 425 kg / 937 lb | 101 | 825 kg / 1819 lb | 124 | 1600 kg / 3527 lb |
| 79 | 437 kg / 963 lb | 102 | 850 kg / 1874 lb | 125 | 1650 kg / 3638 lb |
| 80 | 450 kg / 992 lb | 103 | 875 kg / 1929 lb | 126 | 1700 kg / 3748 lb |
| 81 | 462 kg / 1019 lb | 104 | 900 kg / 1984 lb | ||
| 82 | 475 kg / 1047 lb | 105 | 925 kg / 2039 lb |
Standard values from the ETRTO load index table as listed in Wikipedia: Tire code. Pounds converted and rounded.
Speed symbol table
| Symbol | km/h | mph |
|---|---|---|
| L | 120 | 75 |
| M | 130 | 81 |
| N | 140 | 87 |
| P | 150 | 93 |
| Q | 160 | 99 |
| R | 170 | 106 |
| S | 180 | 112 |
| T | 190 | 118 |
| U | 200 | 124 |
| H | 210 | 130 |
| V | 240 | 149 |
| W | 270 | 168 |
| Y | 300 | 186 |
Standard values as listed in Wikipedia: Tire code. Z or ZR in the size marks a tire for speeds over 240 km/h; the speed symbol after the load index gives the exact rating.
Load index and speed when changing size
Your vehicle’s tire placard and owner’s manual give the tire sizes and the load and speed ratings specified for it. Whether a lower rating is ever allowed depends on local rules. Always check your vehicle owner’s manual, the tire placard in the door jamb, or a tire shop before changing size.
Other markings
Sidewalls also carry a date code (the last four digits of the DOT number give the week and year of manufacture, such as 0422 for week 4 of 2022), winter markings such as M+S and the three-peak mountain snowflake, and an E-mark showing approval under UN rules. Sources: Wikipedia: Tire code.
Frequently asked questions
What do the numbers on a tire mean?
In 225/45R17 94W, 225 is the width in mm, 45 is the sidewall height as a percentage of width, R is radial, 17 is the rim size in inches, 94 is the load index and W is the speed symbol.
What is the load index?
A number code for the maximum load one tire can carry at its reference pressure. 91 is 615 kg, 94 is 670 kg and 100 is 800 kg. The full table is on this page.
What does the speed rating mean?
A letter code for the maximum speed at which the tire can carry its rated load under the standard’s test conditions. H is 210 km/h (130 mph), V is 240 km/h and W is 270 km/h.
What does XL mean on a tire?
XL, Extra Load or RF (reinforced) marks a tire built to carry a higher load than the standard version of the same size, at a higher pressure. The load index shows the actual capacity.
What does the P or LT in front mean?
P marks a passenger tire sized to the US TRA standard; no letter usually means the European ETRTO standard. LT marks a light truck tire. Load capacities in the two systems can differ for the same size.
How do I find how old a tire is?
Look for the DOT code on the sidewall. Its last four digits give the week and year of manufacture: 0422 means the fourth week of 2022.
Last updated: October 15, 2026