255/50R20 tire size
A 255/50R20 tire is 30.0 inches (763 mm) tall and 10.0 inches (255 mm) wide, for a 20-inch wheel. Each sidewall is 5.0 inches (127 mm), 50% of the width, and the tire makes about 671 revolutions a mile.
Sources checked
| Dimension | 255/50R20 |
|---|---|
| Overall diameter | 30.04 in (763 mm) |
| Section width | 10.04 in (255 mm) |
| Sidewall height | 5.02 in (127 mm) |
| Aspect ratio | 50% |
| Rim diameter | 20 in |
| Circumference | 94.4 in (2,397 mm) |
| Revolutions per mile | 671 |
| Revolutions per km | 417 |
Compare 255/50R20 with another size
Metric, LT and flotation
At 60 mph on the speedometer you’re doing
62.0mph
+3.3% · the speedometer reads low
- Height
- +1.00 in (+26 mm)
- Width
- 0.00 in (0 mm)
- Ground clearance
- +0.50 in (+13 mm)
- Each side, same wheel
- 0.00 in (0 mm)
255/50R20 and 255/55R20 side by side
| Dimension | 255/50R20 | 255/55R20 | Change |
|---|---|---|---|
| Overall diameter | 30.04 in (763 mm) | 31.04 in (789 mm) | +1.00 in (+26 mm) |
| Section width | 10.04 in (255 mm) | 10.04 in (255 mm) | 0.00 in (0 mm) |
| Sidewall height | 5.02 in (127 mm) | 5.52 in (140 mm) | +0.50 in (+13 mm) |
| Aspect ratio | 50% | 55% | |
| Rim diameter | 20 in | 20 in | |
| Circumference | 94.4 in | 97.5 in | +3.1 in |
| Revolutions per mile | 671 | 650 | −21 |
| Revolutions per km | 417 | 404 | −13 |
The working
- 255/50R20: sidewall = 255 mm × 50% = 127.5 mm = 5.02 in.
- Diameter = rim + 2 × sidewall = 20 + 2 × 5.02 = 30.04 in (763 mm).
- Circumference = π × 30.04 = 94.4 in; revolutions per mile = 63,360 ÷ 94.4 = 671.
- 255/55R20: sidewall = 255 mm × 55% = 140.3 mm = 5.52 in.
- Diameter = rim + 2 × sidewall = 20 + 2 × 5.52 = 31.04 in (789 mm).
- Circumference = π × 31.04 = 97.5 in; revolutions per mile = 63,360 ÷ 97.5 = 650.
- Speedometer. True speed = what it shows × new diameter ÷ old = 60 × 31.04 ÷ 30.04 = 62.0 mph.
- Ground clearance. Half the change in diameter: (31.04 − 30.04) ÷ 2 = +0.50 in.
Where the 255/50R20 numbers come from
The section width is 255 mm (10.04 inches), and each sidewall is 50% of it: 127.5 mm, or 5.02 inches. Two sidewalls and the 20-inch rim make 30.04 inches (763 mm).
One turn covers π × 30.04 = 94.4 inches, so the tire turns 671 times a mile and 417 times a kilometer.
What tire makers publish for 255/50R20
Inflated on the maker’s measuring rim. The percentage is the printed diameter against the 30.04 inches worked out above.
| Tire | Size as printed | Diameter | Width | Revs per mile |
|---|---|---|---|---|
| Toyo Extensa A/S II | 255/50R20 | 30.1 in (+0.2%) | 10.4 in | 691 |
| Toyo Open Country A/T III | 255/50R20 | 30.1 in (+0.2%) | 10.4 in | 691 |
Other 20-inch sizes against 255/50R20
Each size’s height against 255/50R20, and what a speedometer set for 255/50R20 shows at 60 mph with that size on.
| Size | Diameter | Width | Height change | At 60 mph shown |
|---|---|---|---|---|
| 245/50R20 compared | 29.6 in | 9.6 in | −1.3% | 59.2 mph |
| 255/55R20 compared | 31.0 in | 10.0 in | +3.3% | 62.0 mph |
| 275/55R20 | 31.9 in | 10.8 in | +6.2% | 63.7 mph |
| 275/60R20 | 33.0 in | 10.8 in | +9.8% | 65.9 mph |
| 275/65R20 | 34.1 in | 10.8 in | +13.4% | 68.1 mph |
| 285/55R20 | 32.3 in | 11.2 in | +7.7% | 64.6 mph |
| 285/60R20 | 33.5 in | 11.2 in | +11.4% | 66.8 mph |
| 33x12.50R20 | 33.0 in | 12.5 in | +9.9% | 65.9 mph |
| 35x12.50R20 | 35.0 in | 12.5 in | +16.5% | 69.9 mph |
255/50R20 compared
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 255/50R20 in inches?
About 30.0x10.0R20: 30.0 inches tall and 10.0 inches wide on a 20-inch wheel, with 5.0-inch sidewalls. Exactly, 20 + 2 × 255 mm × 0.50 ÷ 25.4 = 30.04 inches.
How many revolutions per mile does a 255/50R20 make?
671 by its diameter: 63,360 inches in a mile ÷ 94.4 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 LT255/50R20 the same size as P255/50R20?
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.