Tire Size Chart and How to Read the Numbers on a Tire
For drivers replacing tires, comparing sizes or checking whether a different size will fit. The numbers on the sidewall translate directly into width, height and load capacity, and every conversion below is calculated from the size code itself.
A tire size such as P225/65R17 102H means a passenger tire 225 mm (8.9 in) wide, with a sidewall 65% as tall as it is wide (146 mm, 5.8 in), radial construction, for a 17-inch wheel. Its overall diameter is about 28.5 in (724 mm); load index 102 = 1,874 lb (850 kg) per tire, and H = 130 mph (210 km/h).
- Example size
- P225/65R17 102H
- Diameter
- 28.5 in (724 mm)
- Section width
- 8.9 in (225 mm)
- Max load (102)
- 1,874 lb (850 kg)
On this page
- How to read a tire size
- Tire size chart: diameter and width of common sizes
- P-metric, LT, Euro-metric and flotation sizes
- Load index chart
- Speed rating chart
- Where to find the right tire size for your vehicle
- Changing tire size: the 3% rule and plus-sizing
- Tread depth: new, worn and legal
- Tire sizes for other vehicles
- Frequently asked questions
How to read a tire size
Every car and light-truck tire carries the same code on its sidewall. Read it left to right. The example below is a common size on compact SUVs.
| Part | Example | Meaning |
|---|---|---|
| Service type | P | Passenger tire (P-metric). LT = light truck, ST = special trailer, T = temporary spare. No letter usually means a Euro-metric passenger tire. |
| Section width | 225 | Width in millimeters from sidewall to sidewall, measured on the specified rim: 225 mm = 8.86 in |
| Aspect ratio | 65 | Sidewall height as a percentage of width: 225 × 0.65 = 146 mm (5.76 in) |
| Construction | R | Radial. D or a dash = bias-ply; B = bias-belted |
| Wheel diameter | 17 | Fits a 17-inch wheel (measured at the bead seat, in inches even on metric tires) |
| Load index | 102 | Maximum load per tire at maximum pressure: 850 kg (1,874 lb) |
| Speed rating | H | Maximum sustained speed at rated load: 130 mph (210 km/h) |
Two more codes sit nearby. The DOT code ends in four digits giving the week and year of manufacture (2524 = week 25 of 2024). The UTQG line on passenger tires shows a treadwear number, a traction grade (AA to C) and a temperature grade (A to C). Treadwear is a comparison between tires of the same brand, not a mileage figure.
Working out overall diameter
- Sidewall height. Width × aspect ratio ÷ 100. For 225/65: 225 × 0.65 = 146.25 mm.
- Both sidewalls. Double it: 292.5 mm, which is 11.52 in.
- Add the wheel. 17 in + 11.52 in = 28.5 in overall diameter (724 mm).
Real tires vary by a few millimeters from the calculated figure because each tread pattern and casing grows differently when inflated. Manufacturers publish the measured diameter in their spec tables, and it is usually within 1% of the math.
Tire size chart: diameter and width of common sizes
Calculated from the size codes. Sizes are grouped roughly from small cars to full-size pickups; the same size is often fitted to many models.
| Size | Overall diameter | Section width | Sidewall height | Typical vehicles |
|---|---|---|---|---|
| 195/65R15 | 25.0 in (635 mm) | 7.7 in | 5.0 in | Subcompact and older compact cars |
| 205/55R16 | 24.9 in (632 mm) | 8.1 in | 4.4 in | Compact sedans and hatchbacks |
| 215/55R17 | 26.3 in (668 mm) | 8.5 in | 4.7 in | Midsize sedans |
| 225/45R17 | 25.0 in (634 mm) | 8.9 in | 4.0 in | Sport trims of compact cars |
| 235/45R18 | 26.3 in (669 mm) | 9.3 in | 4.2 in | Midsize sedans on 18-in wheels |
| 225/65R17 | 28.5 in (724 mm) | 8.9 in | 5.8 in | Compact SUVs and crossovers |
| 235/65R17 | 29.0 in (737 mm) | 9.3 in | 6.0 in | Midsize crossovers, minivans |
| 235/55R19 | 29.2 in (741 mm) | 9.3 in | 5.1 in | Upper trims of compact and midsize SUVs |
| 245/60R18 | 29.6 in (751 mm) | 9.6 in | 5.8 in | Midsize SUVs, three-row crossovers |
| 255/55R20 | 31.0 in (788 mm) | 10.0 in | 5.5 in | Large SUVs on 20-in wheels |
| 265/70R17 | 31.6 in (803 mm) | 10.4 in | 7.3 in | Full-size and midsize pickups, body-on-frame SUVs |
| 275/65R18 | 32.1 in (815 mm) | 10.8 in | 7.0 in | Full-size pickups |
| 275/60R20 | 33.0 in (838 mm) | 10.8 in | 6.5 in | Full-size pickups and SUVs on 20-in wheels |
| 285/70R17 | 32.7 in (831 mm) | 11.2 in | 7.9 in | Off-road trims, the usual "33-inch" upgrade |
| 315/70R17 | 34.4 in (873 mm) | 12.4 in | 8.7 in | Off-road trims, the usual "35-inch" upgrade |
The table shows why the wheel number alone says little about size. A 225/45R17 and a 195/65R15 are the same height (25.0 in) because the lower aspect ratio offsets the bigger wheel. That is the principle behind plus-sizing, covered below. For the wheel side of the fitment (bolt pattern, offset, rim width), see the wheel size guide.
P-metric, LT, Euro-metric and flotation sizes
The same width and aspect ratio can appear with different prefixes, and they are not interchangeable.
- P-metric (P225/65R17): the US passenger standard (TRA). Load is set by the load index.
- Euro-metric (225/65R17): the ETRTO passenger standard, interchangeable with the P-metric size as long as the load index is at least as high. XL (extra load) or RF (reinforced) tires carry more at a higher pressure, usually up to 50 psi instead of 35 psi for the rated load.
- LT (LT265/70R17 121/118S): light-truck tires with a stiffer casing and a load range letter. Load range C is inflated up to 50 psi, D to 65 psi, E to 80 psi. The two load indexes are single and dual-wheel ratings.
- Flotation (33x12.50R15LT): sizes stated in inches: about 33 in tall, 12.5 in wide, for a 15-inch wheel. Used for off-road tires.
- ST: trailer-only tires. Never fit them to a car or truck. Their sizing and load ranges are explained in the trailer tire size guide.
An LT tire fitted to a half-ton truck in place of the original P-metric size needs a higher pressure to carry the same load, and may ride harder. Going the other way (P-metric on a truck specified for LT tires) can leave the tire overloaded. Match the load the door placard requires, not just the size.
Load index chart
The load index is the maximum weight one tire carries at its maximum inflation pressure. Multiply by four for the set and compare with the vehicle's gross axle ratings, not its curb weight.
| Load index | Max load (lb) | Max load (kg) | Load index | Max load (lb) | Max load (kg) |
|---|---|---|---|---|---|
| 85 | 1,135 | 515 | 104 | 1,984 | 900 |
| 88 | 1,235 | 560 | 107 | 2,150 | 975 |
| 91 | 1,356 | 615 | 110 | 2,337 | 1,060 |
| 94 | 1,477 | 670 | 112 | 2,469 | 1,120 |
| 96 | 1,565 | 710 | 115 | 2,679 | 1,215 |
| 98 | 1,653 | 750 | 116 | 2,756 | 1,250 |
| 100 | 1,764 | 800 | 118 | 2,910 | 1,320 |
| 102 | 1,874 | 850 | 121 | 3,197 | 1,450 |
Speed rating chart
The letter after the load index is the highest speed the tire can sustain at its rated load. The ratings are defined in km/h; the mph values are conversions.
| Rating | mph | km/h | Typical use |
|---|---|---|---|
| L | 75 | 120 | Off-road light-truck tires |
| N | 87 | 140 | Temporary spares (T-type) |
| Q | 99 | 160 | Some winter and mud-terrain tires |
| R | 106 | 170 | Light-truck all-terrain tires |
| S | 112 | 180 | Family cars, minivans, pickups |
| T | 118 | 190 | Family cars, crossovers |
| H | 130 | 210 | Most sedans and SUVs |
| V | 149 | 240 | Sport sedans, performance trims |
| W | 168 | 270 | Performance cars |
| Y | 186 | 300 | High-performance cars; (Y) means above 186 mph |
Replacement tires should match or exceed the original speed rating on all four corners. Winter tires are the accepted exception: many makers allow a lower rating if the driver keeps to the lower limit.
Where to find the right tire size for your vehicle
- Driver's door jamb: the Tire and Loading Information placard required by FMVSS 110 lists the original tire size and the cold inflation pressures, front and rear. This pressure, usually 30-36 psi on cars and crossovers, is the one to use.
- Owner's manual: lists every size offered on each trim, which matters if your car came with different wheel options.
- The tire itself: shows what is fitted now, which may not be the original size on a used car.
The number molded into the sidewall next to "Max. Press." is the tire's limit, not a recommended pressure.
Changing tire size: the 3% rule and plus-sizing
A new size should stay within about 3% of the original overall diameter. Bigger differences upset the speedometer, ABS and stability-control readings, and may rub. Plus-sizing keeps the diameter while the wheel grows and the sidewall shrinks:
| Option | Size | Overall diameter | Difference |
|---|---|---|---|
| Original | 205/55R16 | 24.9 in (632 mm) | 0 |
| Plus one | 225/45R17 | 25.0 in (634 mm) | +0.4% |
| Plus two | 225/40R18 | 25.1 in (637 mm) | +0.8% |
| Minus one (winter set) | 195/65R15 | 25.0 in (635 mm) | +0.4% |
Speedometer effect: the reading is off by the same percentage as the diameter change. Going from 225/65R17 (28.5 in) to 235/65R17 (29.0 in) is +1.8%, so at an indicated 60 mph you are doing about 61.1 mph. Taller tires make the speedometer read low.
Clearance is the other limit. Each extra 10 mm of width moves the inner sidewall about 5 mm closer to the suspension, and each 1 in of extra diameter lifts the tire 0.5 in toward the fender liner. Check at full steering lock and with the suspension compressed.
Tread depth: new, worn and legal
| State | Inches | Millimeters |
|---|---|---|
| New passenger tire | 10/32 to 11/32 in | 7.9 to 8.7 mm |
| New all-terrain light-truck tire | 12/32 to 15/32 in | 9.5 to 11.9 mm |
| Wet-grip drop-off point (common advice) | 4/32 in | 3.2 mm |
| Legal minimum, most US states | 2/32 in | 1.6 mm |
| Legal minimum, EU and UK cars | 0.063 in | 1.6 mm |
Treadwear indicator bars molded across the grooves become flush with the tread at 2/32 in. A US penny inserted head-first reaches Lincoln's head at about 2/32 in; a quarter reaches Washington's head at about 4/32 in.
Tire sizes for other vehicles
Other vehicles use different size systems, each with its own guide:
- Trailer tires: ST sizes, load ranges and the 65 mph rule.
- Motorcycle tires: metric, inch and alphanumeric codes, front vs rear pairs.
- ATV and UTV tires: three-number sizes such as 25x8-12.
- Bicycle tires: 700c, 29er and ISO/ETRTO bead seat sizes.
Frequently asked questions
How do I calculate a tire's height from its size?
Multiply the width by the aspect ratio to get the sidewall height, double it, and add the wheel diameter. For 265/70R17: 265 × 0.70 = 185.5 mm per sidewall, × 2 = 371 mm (14.6 in), plus 17 in = 31.6 in overall.
Can I put a different tire size on my car?
Yes, if the new size keeps the overall diameter within about 3% of the original, has a load index at least as high, fits the wheel's approved width range and clears the suspension and fenders at full steering lock. Sizes printed on your door placard are the ones the vehicle was certified with.
What does the R in a tire size mean?
R means radial construction, where the body plies run straight across the tire at 90° to the direction of travel. Almost every car and light-truck tire sold today is radial. A dash (-) or D means bias-ply and B means bias-belted, both mainly found on trailer, motorcycle and ATV tires.
What tire size is a 33-inch tire in metric?
The closest metric sizes are 285/75R16 (32.8 in), 285/70R17 (32.7 in), 285/65R18 (32.6 in) and 285/60R20 (33.5 in), all within 2% of 33 in. Flotation sizes such as 33x12.50R15 state the diameter directly.
Is a 235 tire much wider than a 225?
The section width grows by exactly 10 mm (0.39 in). Because the aspect ratio is a percentage of width, the sidewall also grows: 235/65R17 is 13 mm (0.5 in) taller overall than 225/65R17.
How old can a tire be?
The four-digit DOT date code gives the week and year it was made, so 1523 means week 15 of 2023. Many vehicle makers advise replacing tires six years after manufacture regardless of tread depth, and tire makers generally set ten years as the maximum service life.