How to Read Mud Tire Sizes: A Simple Guide to Every Number Shown
Last updated on October 20th, 2026 at 06:47 am
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Mud tire sizes come in two formats. Metric sizes such as LT285/75R16 give width in millimeters, then aspect ratio, then wheel diameter in inches. Flotation sizes such as 35x12.50R17 are already in inches: overall tire diameter, section width, then wheel diameter.
A metric tire reaches a flotation tire’s height only after some math, which is why 285/75R16 is sold as a “33”: it works out to about 32.8 inches tall. The decoder below does that math and also reads the load index and speed symbol.
Every number on the sidewall
Metric size: LT285/75R16 126/123R E
| Part | Meaning |
|---|---|
| LT | Light truck tire. A leading P means passenger |
| 285 | Section width in millimeters, about 11.2 inches |
| 75 | Aspect ratio: sidewall height is 75% of the width |
| R | Radial construction |
| 16 | Wheel (rim) diameter in inches |
| 126/123 | Load index: 126 for a single tire (3,748 lb), 123 for dual use (3,417 lb) |
| R (after the load index) | Speed symbol, up to 106 mph |
| E | Load range E, equal to a 10-ply rating |
Flotation size: 35x12.50R17
35 is the approximate overall diameter in inches, 12.50 the approximate section width in inches, R means radial, and 17 is the wheel diameter. Flotation sizes are common on mud-terrain tires because they state height directly. They are nominal, so two 35s from different makers can differ by a few tenths of an inch.
Convert metric sizes to inches
The overall diameter in inches is the section width times the aspect ratio, divided by 1,270, plus the wheel diameter. For a 285/75R16, 285 × 75 ÷ 1,270 = 16.8, plus 16 gives 32.8 inches.
| Metric size | Overall diameter | Section width | Often sold as |
|---|---|---|---|
| 265/70R17 | 31.6 in | 10.4 in | 31 in |
| 275/65R18 | 32.1 in | 10.8 in | 32 in |
| 285/75R16 | 32.8 in | 11.2 in | 33 in |
| 285/70R17 | 32.7 in | 11.2 in | 33 in |
| 305/55R20 | 33.2 in | 12.0 in | 33 in |
| 315/70R17 | 34.4 in | 12.4 in | 35 in |
| 325/60R20 | 35.4 in | 12.8 in | 35 in |
A 315 is not a 35. The 315 is a width in millimeters, and the 35 is a height in inches. A 315/70R17 stands about 34.4 inches tall, while a 315/55R20 is shorter.
Decode your own tire size
Type the size as printed on the sidewall. Add your current size to see the diameter and speedometer difference.
Based on the formulas and tables on Wikipedia’s tire code page. It reads load index 120 to 130 and speed symbols Q to T. For other values, use the chart linked below.
Load range and ply rating
Old tires such as the one above counted real plies. Today a ply rating is a strength rating, not a literal count. LT load ranges run A to N, with B = 4, C = 6, D = 8, E = 10 and F = 12 plies.
Higher load ranges carry more at higher pressure but ride firmer. Never go below the load capacity your vehicle maker requires. Our tire load index chart checks a tire against your axle rating, and load range C vs D vs E compares the common choices.
Other sidewall markings that matter
- M+S: mud and snow, a manufacturer-declared designation for self-cleaning tread and average traction in mud or heavy snow.
- 3PMSF: the three-peak mountain snowflake, for tires rated for severe snow.
- DOT code: the last four digits are the build date: the first two the week, the last two the year. “0221” is the second week of 2021.
- UTQG: treadwear, traction and temperature grades. Many LT tires are exempt, so you may not see it.
- Max pressure: the number molded on the sidewall is the tire’s limit, not the pressure to run. Start from the placard on the driver-door jamb.
Check fit before you buy
- Measure clearance at full steering lock and full suspension compression; taller or wider tires can rub.
- Check wheel width against the tire maker’s approved rim range.
- Expect the speedometer, odometer and effective gearing to change with a taller tire.
Our tire size calculator shows speedometer error and clearance, the backspacing guide for 35s covers rub, and a digital pressure gauge helps you set pressure once the tires are on.
FAQ
It is the section width in inches on a flotation size, so 35x12.50R17 is 12.5 inches wide.
A 285/75R16 or 285/70R17 is about 32.7 to 32.8 inches tall, which is sold as a 33. Other 285 sizes with a lower aspect ratio are shorter.
A 315/70R17 is about 34.4 inches tall and is commonly sold as a 35. Other 315 sizes vary with aspect ratio and rim size.
Light truck. LT tires have heavier construction and are made for higher loads than P-metric tires, with a firmer ride.
Extra load. It does not mean extra large.
Source: Wikipedia: Tire code.
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I'm Suryashankar Dasgupta, the founder of Off-Road Handbook. I've been off-roading for years in the USA, including California and Texas, and have ridden mountain and desert terrain abroad. I've also driven a Jeep Compass for more than seven years, so I know the day-to-day side of Jeep ownership first-hand, from the Uconnect screen to the warning lights. Every guide here is researched from manufacturer owner's manuals, NHTSA recall and service-bulletin records and other trusted sources, checked against them before it is published, and corrected when we find a mistake. You can read how we work in our editorial policy: https://offroadhandbook.com/editorial-policy/
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