Pickup and Light-Truck Tire Size Charts and Conversions: Reading the Sidewall Numbers
How to read LT-metric, P-metric, flotation and older truck tire sizes, convert them to inches, compare overall diameter, and understand what the calculations cannot show.
Contents
- How do you read a light-truck tire size on the sidewall?
- Dimensions, ratios and ratings are different kinds of numbers
- What truck tire size formats are used on pickups and light trucks?
- How flotation tire sizes differ from metric sizes
- LT vs metric tires: what is the difference?
- Load range on LT tire markings
- How do you convert truck tire sizes between metric and inches?
- Converting a metric size to inches
- Converting a flotation size to approximate metric terms
- Calculating circumference and revolutions per mile
- Truck tire size chart in inches
- Old truck tire size conversion chart: reading legacy truck tire sizes
- How do differences in width, aspect ratio and rim diameter affect tire size?
- Worked comparison: 265/70R17 vs 285/75R17
- Same width, different aspect ratio
- What calculated tire sizes cannot tell you
A pickup or light-truck tire size such as LT265/70R17 121/118S Load Range E describes the tire's dimensions and its load and speed ratings. LT means light truck. 265 is the section width in millimeters. 70 is the aspect ratio, so the sidewall height is 70% of the width. R means radial construction. 17 is the rim diameter in inches. 121/118 are the load indexes for single and dual mounting. S is the speed rating, and Load Range E shows the tire's strength class.
To convert a metric size to inches, follow three steps:
- Multiply the width by the aspect ratio to get the sidewall height in millimeters.
- Divide that figure by 25.4 to get inches.
- Add twice the sidewall height to the rim diameter. The result is the calculated overall diameter.
For LT265/70R17, this gives a sidewall of about 7.30 in and an overall diameter of about 31.6 in.
These figures are calculated geometry. They are not measured dimensions, and they do not confirm that a tire fits a particular truck.
How do you read a light-truck tire size on the sidewall?
A light-truck tire size has three dimensional values: section width, aspect ratio and rim diameter. It also has letters for tire type and construction, and service ratings for load and speed. The table below separates each marking in an LT-metric size by type and unit.
| Marking (example LT265/70R17 121/118S) | What it is | Unit | What you can compare with it |
|---|---|---|---|
| LT | Tire type: light truck | Letter code | Shows that the tire is built and rated to light-truck load standards, not passenger standards |
| 265 | Section width (nominal) | Millimeters | Width of the tire from sidewall to sidewall on its specified measuring rim; 265 mm is about 10.43 in |
| 70 | Aspect ratio | Percent (ratio, not a length) | Sidewall height as a share of width; a lower number means a shorter sidewall at the same width |
| R | Construction | Letter code | R means radial; a dash (as in older sizes like 7.50-16) indicates bias construction |
| 17 | Rim diameter | Inches | Must match the wheel diameter exactly |
| 121/118 | Load index, single/dual | Index number (coded value) | 121 = 1,450 kg (about 3,195 lb) per tire in single use; 118 = 1,320 kg (about 2,910 lb) per tire in dual use |
| S | Speed rating | Letter code | S = 112 mph (180 km/h) maximum under rated conditions |
| Load Range E | Load range (strength class) | Letter code | Indicates a construction strength comparable to a historical 10-ply rating and the tire's maximum inflation class |
The sidewall also states the maximum load and maximum inflation pressure in pounds and psi, plus kilograms and kPa. Those printed limits are the authority for that specific tire. The size string alone does not give them.
Dimensions, ratios and ratings are different kinds of numbers
Only the section width and rim diameter are physical lengths, and they use different units. Width is in millimeters, and rim diameter is in inches.
The aspect ratio is a percentage. It produces a length only when you multiply it by the width.
Load index and speed rating are codes that refer to standard tables. A higher load index means more capacity, but the numbers do not scale linearly. A load index of 121 is not 21% stronger than 100.
What truck tire size formats are used on pickups and light trucks?
Pickups and light trucks use five main size formats. Each format writes dimensions differently, so you need to know which one you are reading before comparing sizes.
| Format | Example | How dimensions are written | Typical use |
|---|---|---|---|
| LT-metric | LT275/70R18 125/122S | Width in mm, aspect ratio in %, rim in inches; LT prefix | 3/4-ton and 1-ton pickups, towing and hauling, heavy-duty off-road use |
| P-metric | P265/70R17 113T | Same geometry as LT-metric; P prefix | Passenger cars, SUVs and many half-ton pickups |
| Euro-metric | 265/70R17 115T or 235/65R16C | Same geometry, no prefix; C suffix marks commercial (van/light truck) tires | SUVs, crossovers, vans and some pickups |
| Flotation | 35x12.50R17LT 121Q | Overall diameter in inches x section width in inches, R, rim diameter in inches | Larger off-road and lifted trucks |
| Legacy numeric | 7.50R16LT or 7.50-16 8PR | Section width in inches and rim diameter in inches; aspect ratio not stated | Older trucks, vintage vehicles, some utility and trailer uses |
How flotation tire sizes differ from metric sizes
In a flotation size, the first number is the tire's nominal overall diameter in inches. In a metric size, the first number is the section width in millimeters.
For example, 35x12.50R17LT means a tire of about 35 in overall diameter and 12.50 in section width, for a 17 in rim. You can read the overall diameter directly, without calculation. To find the sidewall height, subtract the rim diameter from the overall diameter and divide by two. For this tire, (35 - 17) / 2 = 9 in.
LT vs metric tires: what is the difference?
LT-metric and P-metric tires with the same numbers have the same calculated dimensions. They differ in construction, load rating and inflation range.
An LT tire is designed to carry heavier loads at higher inflation pressures. It is usually built with a stronger internal structure and is marked with a load range. A P-metric tire is rated to passenger-tire load tables.
When a P-metric tire is used on a light truck, U.S. load tables typically reduce its rated capacity. They do this by dividing the passenger load figure by 1.10.
Euro-metric tires have no prefix and use their own load tables. Some are marked XL (extra load). C-type Euro-metric sizes, such as 235/65R16C, are commercial tires with dual load indexes, similar in purpose to LT tires.
Matching the size numbers alone does not mean two tires can carry the same load. Compare load index, load range and maximum inflation pressure as well.
Load range on LT tire markings
Load range is a letter that groups light-truck tires by strength and inflation capability. Each letter replaces an older ply rating.
| Load range | Equivalent ply rating | Typical maximum inflation (LT-metric) |
|---|---|---|
| C | 6-ply rating | About 50 psi |
| D | 8-ply rating | About 65 psi |
| E | 10-ply rating | About 80 psi |
| F | 12-ply rating | Higher; varies by size |
A ply rating describes strength, not the actual number of plies inside the tire. The pressures listed above are typical values only. The maximum load and maximum pressure printed on the individual tire's sidewall are the limits that apply.
How do you convert truck tire sizes between metric and inches?
A truck tire size conversion turns metric markings into inches, or flotation markings into approximate metric terms. It uses simple geometry: sidewall height comes from width and aspect ratio, and overall diameter equals rim diameter plus two sidewalls.
Converting a metric size to inches
- Multiply the section width by the aspect ratio as a decimal. For LT285/75R16: 285 x 0.75 = 213.75 mm sidewall height.
- Convert the sidewall to inches: 213.75 / 25.4 = 8.42 in.
- Calculate overall diameter: 16 + (2 x 8.42) = 32.83 in.
- Convert the section width to inches: 285 / 25.4 = 11.22 in.
- Write the result in flotation style if you need it: about 32.8 x 11.2 in for a 16 in rim.
This is why LT285/75R16 is often grouped with 33-inch tires. Its calculated diameter is just under 33 in.
Converting a flotation size to approximate metric terms
- Convert the width to millimeters. For 33x12.50R15: 12.50 x 25.4 = 317.5 mm.
- Find the sidewall height: (33 - 15) / 2 = 9 in, which is 228.6 mm.
- Find the implied aspect ratio: 228.6 / 317.5 = 0.72, or about 72%.
The result, about 318 mm wide with a 72% profile, rarely matches a standard metric size exactly. In practice, a flotation-to-metric conversion means finding the closest available size, not an identical one.
Calculating circumference and revolutions per mile
Circumference is the distance a tire travels in one revolution. It equals the overall diameter multiplied by pi (about 3.1416).
For LT265/70R17, with a calculated diameter of 31.61 in, the circumference is about 99.3 in. That gives about 63,360 / 99.3 = 638 revolutions per mile, because a mile has 63,360 inches.
Revolutions-per-mile figures published by manufacturers are measured on loaded tires. They usually differ from this unloaded calculation.
Truck tire size chart in inches
The pickup tire size chart below lists calculated dimensions for common light-truck sizes. All values are in inches. They were calculated from the nominal size markings and are not manufacturer measurements.
| Tire size | Section width (in) | Sidewall height (in) | Overall diameter (in) | Circumference (in) |
|---|---|---|---|---|
| 245/75R16 | 9.65 | 7.23 | 30.47 | 95.72 |
| 265/75R16 | 10.43 | 7.83 | 31.65 | 99.43 |
| 285/75R16 | 11.22 | 8.42 | 32.83 | 103.14 |
| 315/75R16 | 12.40 | 9.30 | 34.60 | 108.71 |
| 265/70R17 | 10.43 | 7.30 | 31.61 | 99.29 |
| 285/70R17 | 11.22 | 7.85 | 32.71 | 102.76 |
| 285/75R17 | 11.22 | 8.42 | 33.83 | 106.28 |
| 315/70R17 | 12.40 | 8.68 | 34.36 | 107.95 |
| 275/65R18 | 10.83 | 7.04 | 32.07 | 100.77 |
| 275/70R18 | 10.83 | 7.58 | 33.16 | 104.17 |
| 275/60R20 | 10.83 | 6.50 | 32.99 | 103.65 |
| 33x12.50R15 | 12.50 | 9.00 | 33.00 | 103.67 |
| 35x12.50R17 | 12.50 | 9.00 | 35.00 | 109.96 |
| 35x12.50R20 | 12.50 | 7.50 | 35.00 | 109.96 |
| 37x12.50R17 | 12.50 | 10.00 | 37.00 | 116.24 |
The chart shows that overall diameter can stay similar while proportions change. For example, 275/70R18 (33.16 in) and 275/60R20 (32.99 in) are almost the same height. The 20 in size gets there with a larger wheel and a sidewall about 1.1 in shorter.
The same applies to 35x12.50R17 and 35x12.50R20. Both have a nominal 35 in diameter, but the sidewall height is 9 in on the 17 in size and 7.5 in on the 20 in size.
Old truck tire size conversion chart: reading legacy truck tire sizes
Legacy numeric tire designations, such as 7.50-16 or 7.50R16, state the section width in inches followed by the rim diameter in inches. They do not state an aspect ratio. These older sizes were tall and narrow by modern standards.
In 7.50-16 8PR, the tire is about 7.50 in wide, fits a 16 in rim, uses bias construction (the dash) and has an 8-ply rating. The same size with R, as in 7.50R16, is a radial version.
Modern metric equivalents for legacy sizes are approximate. The comparison should be based on overall diameter and load capacity.
| Legacy size | Commonly listed metric counterpart | Comparison note |
|---|---|---|
| 7.50R16 / 7.50-16 | 235/85R16 | 235/85R16 calculates to about 31.7 in overall diameter and 9.25 in section width; confirm the load range matches the original requirement |
| 8.75R16.5, 9.50R16.5 | No direct 16 in substitute | 16.5 in tires fit only 16.5 in rims; changing to a 16 in tire requires 16 in wheels |
A 16 in tire and a 16.5 in tire are not interchangeable on the same wheel. The bead seat diameters are different, and mounting the wrong combination is dangerous.
When converting any legacy size, start with the rim diameter. It must match exactly. Then compare overall diameter and load capacity.
How do differences in width, aspect ratio and rim diameter affect tire size?
Each of the three dimensional values changes the tire's geometry in its own way.
- Width changes the section width directly. It also changes sidewall height, because sidewall height is a percentage of width.
- Aspect ratio changes the sidewall height at a given width.
- Rim diameter adds to overall diameter inch for inch.
Overall diameter determines circumference. Circumference determines how far the truck travels per wheel revolution.
Worked comparison: 265/70R17 vs 285/75R17
- Width: 285 mm vs 265 mm is 20 mm wider, or about 0.79 in.
- Sidewall: 8.42 in vs 7.30 in is about 1.11 in taller per side.
- Overall diameter: 33.83 in vs 31.61 in is about 2.22 in larger, or 7.0%.
- Circumference: 106.28 in vs 99.29 in is about 7 in more travel per revolution.
- Ground clearance: the axle center rises by about half the diameter difference, roughly 1.1 in. This is calculated, before tire deflection under load.
A 7.0% larger diameter means the speedometer, if calibrated for 265/70R17, reads low. At an indicated 60 mph, the truck would travel about 64.2 mph (60 x 33.83 / 31.61).
The same percentage applies to the odometer. The larger circumference also changes the effective gearing in the same proportion.
Same width, different aspect ratio
285/70R17 and 285/75R17 have the same 11.22 in section width. The change from 70 to 75 adds 5% of 285 mm, which is 14.25 mm (about 0.56 in), to each sidewall. That increases the overall diameter by about 1.12 in.
What calculated tire sizes cannot tell you
Calculated dimensions are nominal geometry from the size marking. Actual tire dimensions and vehicle fitment are separate questions.
- Actual dimensions vary: real overall diameter and section width depend on the manufacturer, tread design, tread depth and the width of the rim the tire is mounted on. Two tires with the same size marking can measure differently.
- Flotation numbers are nominal: a tire marked 35 in can measure smaller or larger than 35 in. The manufacturer's specification lists the measured overall diameter.
- Loaded radius is smaller: under vehicle weight, the distance from axle to ground is less than half the unloaded diameter.
- Rim width matters: each size has an approved range of rim widths, and section width changes with the rim used.
- Fitment is not geometry: fitment depends on clearance to suspension, fenders and frame, plus wheel offset, steering travel, suspension compression, and brake and ABS/stability system behavior. The required load capacity on the vehicle's tire placard also matters. A size chart does not check any of these.
Use a truck tire size guide or conversion chart to understand what the sidewall numbers mean and how two sizes differ on paper. Then confirm the tire's actual specifications, its load and inflation ratings, and the vehicle manufacturer's requirements before treating a size as a match.