255/55R18 tire size
A 255/55R18 tire is 29.0 inches (738 mm) tall and 10.0 inches (255 mm) wide, for a 18-inch wheel. Each sidewall is 5.5 inches (140 mm), 55% of the width, and the tire makes about 694 revolutions a mile.
Sources checked
| Dimension | 255/55R18 |
|---|---|
| Overall diameter | 29.04 in (738 mm) |
| Section width | 10.04 in (255 mm) |
| Sidewall height | 5.52 in (140 mm) |
| Aspect ratio | 55% |
| Rim diameter | 18 in |
| Circumference | 91.2 in (2,318 mm) |
| Revolutions per mile | 694 |
| Revolutions per km | 431 |
Compare 255/55R18 with another size
Metric, LT and flotation
A 255/55R18 tire is
29.0in tall738mm
on a 18-inch wheel
- Width
- 10.04 in (255 mm)
- Sidewall
- 5.52 in (140 mm)
- Circumference
- 91.2 in
- Revolutions per mile
- 694
255/55R18 in full
| Dimension | 255/55R18 |
|---|---|
| Overall diameter | 29.04 in (738 mm) |
| Section width | 10.04 in (255 mm) |
| Sidewall height | 5.52 in (140 mm) |
| Aspect ratio | 55% |
| Rim diameter | 18 in |
| Circumference | 91.2 in |
| Revolutions per mile | 694 |
| Revolutions per km | 431 |
The working
- 255/55R18: sidewall = 255 mm × 55% = 140.3 mm = 5.52 in.
- Diameter = rim + 2 × sidewall = 18 + 2 × 5.52 = 29.04 in (738 mm).
- Circumference = π × 29.04 = 91.2 in; revolutions per mile = 63,360 ÷ 91.2 = 694.
Where the 255/55R18 numbers come from
The section width is 255 mm (10.04 inches), and each sidewall is 55% of it: 140.3 mm, or 5.52 inches. Two sidewalls and the 18-inch rim make 29.04 inches (738 mm).
One turn covers π × 29.04 = 91.2 inches, so the tire turns 694 times a mile and 431 times a kilometer.
What tire makers publish for 255/55R18
Inflated on the maker’s measuring rim. The percentage is the printed diameter against the 29.04 inches worked out above.
| Tire | Size as printed | Diameter | Width | Revs per mile |
|---|---|---|---|---|
| Toyo Open Country A/T III | 255/55R18 | 29 in (−0.1%) | 10.4 in | 716 |
Other 18-inch sizes against 255/55R18
Each size’s height against 255/55R18, and what a speedometer set for 255/55R18 shows at 60 mph with that size on.
| Size | Diameter | Width | Height change | At 60 mph shown |
|---|---|---|---|---|
| 225/40R18 | 25.1 in | 8.9 in | −13.6% | 51.8 mph |
| 225/45R18 | 26.0 in | 8.9 in | −10.6% | 53.7 mph |
| 225/55R18 | 27.7 in | 8.9 in | −4.5% | 57.3 mph |
| 225/60R18 | 28.6 in | 8.9 in | −1.4% | 59.1 mph |
| 235/45R18 | 26.3 in | 9.3 in | −9.4% | 54.4 mph |
| 235/50R18 | 27.3 in | 9.3 in | −6.2% | 56.3 mph |
| 235/55R18 | 28.2 in | 9.3 in | −3.0% | 58.2 mph |
| 235/60R18 | 29.1 in | 9.3 in | +0.2% | 60.1 mph |
| 235/65R18 | 30.0 in | 9.3 in | +3.4% | 62.0 mph |
| 245/40R18 | 25.7 in | 9.6 in | −11.5% | 53.1 mph |
| 245/45R18 | 26.7 in | 9.6 in | −8.1% | 55.1 mph |
| 245/60R18 | 29.6 in | 9.6 in | +1.8% | 61.1 mph |
| 255/70R18 | 32.1 in | 10.0 in | +10.4% | 66.2 mph |
| 265/60R18 | 30.5 in | 10.4 in | +5.1% | 63.1 mph |
| 265/65R18 | 31.6 in | 10.4 in | +8.7% | 65.2 mph |
| 265/70R18 | 32.6 in | 10.4 in | +12.3% | 67.4 mph |
| 275/65R18 | 32.1 in | 10.8 in | +10.4% | 66.3 mph |
| 275/70R18 | 33.2 in | 10.8 in | +14.2% | 68.5 mph |
| 285/65R18 | 32.6 in | 11.2 in | +12.2% | 67.3 mph |
| 35x12.50R18 | 35.0 in | 12.5 in | +20.5% | 72.3 mph |
Every size: the tire size calculator. With the wheels off, the nuts go back on at your vehicle’s lug nut torque.
Questions
What is 255/55R18 in inches?
About 29.0x10.0R18: 29.0 inches tall and 10.0 inches wide on a 18-inch wheel, with 5.5-inch sidewalls. Exactly, 18 + 2 × 255 mm × 0.55 ÷ 25.4 = 29.04 inches.
How many revolutions per mile does a 255/55R18 make?
694 by its diameter: 63,360 inches in a mile ÷ 91.2 inches a turn. Tire makers’ published figures are measured under load, when the tire rolls on a slightly smaller radius, and run 2.8% to 3.3% higher in Toyo’s tables.
Is LT255/55R18 the same size as P255/55R18?
In dimensions, yes: the numbers mean the same in every metric size. The letters mark what the tire is built for, and an LT tire’s load is rated differently, so check the load index and pressure your vehicle needs before swapping one for the other.
Sources
- Bridgestone Americas: Determining tire size: P-metric, Euro-metric, LT-metric, C-type and flotation sizes, and what each number means (checked October 28, 2026)
- Toyo Tires: Extensa A/S II sizes and specifications: inflated overall diameter and width, revolutions per mile (checked October 28, 2026)
- Toyo Tires: Proxes Sport A/S sizes and specifications: inflated overall diameter and width, revolutions per mile (checked October 28, 2026)
- Toyo Tires: Open Country A/T III sizes and specifications: P-metric, LT-metric and flotation sizes, with revolutions per mile (checked October 28, 2026)
- Nitto Tire: Trail Grappler M/T sizes and specs: inflated overall diameter and width, LT-metric and flotation sizes (checked October 28, 2026)
Spotted a number that doesn’t match your manual or a source? Tell us; corrections are logged on the sources page.