Guide

How to read a tire size

In 265/70R17, 265 is the section width in millimetres, 70 is the aspect ratio (sidewall height as % of width), R means radial construction and 17 is the wheel diameter in inches. So the sidewall is 265 × 0.70 = 185.5 mm and the tire is 17 + 2 × 185.5 ÷ 25.4 = 31.6 in tall.

The parts of a metric size

P / LT / none: P = passenger (P-metric), LT = light truck, no letter = Euro-metric. LT and P tires of the same size have the same nominal dimensions but different load ratings at a given pressure; don't swap one for the other without checking the load requirement.
265: section width in mm, measured on a specified measuring rim.
70: aspect ratio, sidewall height as a percentage of width.
R: radial. ZR appears on some high-speed tires.
17: wheel (rim) diameter in inches.
115T: service description, the load index (115) and speed rating (T). See load index & speed rating.

Flotation sizes

33x12.50R20LT gives the overall diameter (33 in), section width (12.50 in) and wheel size (20 in) directly. These are light truck tires. Real flotation tires usually measure a little under their name: in the maker data books we use, most are 0.5–1.5% under.

Try it

Tire size

Metric (265/70R17 or 2657017) or flotation (35x12.50R20)

Where do I find my size?

It's on the tire sidewall, e.g. P265/70R17 115T, and on the tire placard sticker on the driver's door jamb (also in the owner's manual). The placard shows the size the vehicle came with; the sidewall shows what is fitted now. If they differ, use the placard as your starting point. Digits are enough here: 2657017 or 33125020.

FAQ

What does the 70 mean in 265/70R17?

It's the aspect ratio: the sidewall is 70% as tall as the tire is wide (265 mm × 0.70 = 185.5 mm).

What does LT mean on a tire?

Light truck. LT tires are built for heavier loads and higher pressures than P-metric tires of the same size. Use what your placard specifies.

More guides

Nominal vs actual diameter · The 3% rule · AWD and mismatched tires · Load index & speed rating · Revs per mile chart · Tire size chart

Important: These are calculated (nominal) dimensions, not a fitment recommendation. Real tires of the same size differ by brand and model (makers allow about ±3% of section height), and width changes with the rim it is mounted on. The math can't see wheel width and offset, clearance at full steering lock and suspension travel, load index, speed rating, or what your vehicle maker approves. Before changing size, check your door-jamb placard and owner's manual and ask a tire professional. A replacement tire must meet or exceed the load index and speed rating on the placard.