245/40R18 tire size
A 245/40R18 tire is 25.7 inches (653 mm) tall and 9.6 inches (245 mm) wide, for a 18-inch wheel. Each sidewall is 3.9 inches (98 mm), 40% of the width, and the tire makes about 784 revolutions a mile.
Sources checked
| Dimension | 245/40R18 |
|---|---|
| Overall diameter | 25.72 in (653 mm) |
| Section width | 9.65 in (245 mm) |
| Sidewall height | 3.86 in (98 mm) |
| Aspect ratio | 40% |
| Rim diameter | 18 in |
| Circumference | 80.8 in (2,052 mm) |
| Revolutions per mile | 784 |
| Revolutions per km | 487 |
Compare 245/40R18 with another size
Metric, LT and flotation
At 60 mph on the speedometer you’re doing
62.3mph
+3.8% · the speedometer reads low
- Height
- +0.96 in (+25 mm)
- Width
- 0.00 in (0 mm)
- Ground clearance
- +0.48 in (+12 mm)
- Each side, same wheel
- 0.00 in (0 mm)
245/40R18 and 245/45R18 side by side
| Dimension | 245/40R18 | 245/45R18 | Change |
|---|---|---|---|
| Overall diameter | 25.72 in (653 mm) | 26.68 in (678 mm) | +0.96 in (+25 mm) |
| Section width | 9.65 in (245 mm) | 9.65 in (245 mm) | 0.00 in (0 mm) |
| Sidewall height | 3.86 in (98 mm) | 4.34 in (110 mm) | +0.48 in (+12 mm) |
| Aspect ratio | 40% | 45% | |
| Rim diameter | 18 in | 18 in | |
| Circumference | 80.8 in | 83.8 in | +3.0 in |
| Revolutions per mile | 784 | 756 | −28 |
| Revolutions per km | 487 | 470 | −17 |
The working
- 245/40R18: sidewall = 245 mm × 40% = 98.0 mm = 3.86 in.
- Diameter = rim + 2 × sidewall = 18 + 2 × 3.86 = 25.72 in (653 mm).
- Circumference = π × 25.72 = 80.8 in; revolutions per mile = 63,360 ÷ 80.8 = 784.
- 245/45R18: sidewall = 245 mm × 45% = 110.3 mm = 4.34 in.
- Diameter = rim + 2 × sidewall = 18 + 2 × 4.34 = 26.68 in (678 mm).
- Circumference = π × 26.68 = 83.8 in; revolutions per mile = 63,360 ÷ 83.8 = 756.
- Speedometer. True speed = what it shows × new diameter ÷ old = 60 × 26.68 ÷ 25.72 = 62.3 mph.
- Ground clearance. Half the change in diameter: (26.68 − 25.72) ÷ 2 = +0.48 in.
Where the 245/40R18 numbers come from
The section width is 245 mm (9.65 inches), and each sidewall is 40% of it: 98.0 mm, or 3.86 inches. Two sidewalls and the 18-inch rim make 25.72 inches (653 mm).
One turn covers π × 25.72 = 80.8 inches, so the tire turns 784 times a mile and 487 times a kilometer.
What tire makers publish for 245/40R18
Inflated on the maker’s measuring rim. The percentage is the printed diameter against the 25.72 inches worked out above.
| Tire | Size as printed | Diameter | Width | Revs per mile |
|---|---|---|---|---|
| Toyo Proxes Sport A/S | 245/40R18 | 25.7 in (−0.1%) | 9.8 in | 808 |
Other 18-inch sizes against 245/40R18
Each size’s height against 245/40R18, and what a speedometer set for 245/40R18 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 | −2.4% | 58.5 mph |
| 225/45R18 | 26.0 in | 8.9 in | +1.0% | 60.6 mph |
| 225/55R18 | 27.7 in | 8.9 in | +7.9% | 64.7 mph |
| 225/60R18 | 28.6 in | 8.9 in | +11.3% | 66.8 mph |
| 235/45R18 | 26.3 in | 9.3 in | +2.4% | 61.4 mph |
| 235/50R18 | 27.3 in | 9.3 in | +6.0% | 63.6 mph |
| 235/55R18 | 28.2 in | 9.3 in | +9.6% | 65.7 mph |
| 235/60R18 | 29.1 in | 9.3 in | +13.2% | 67.9 mph |
| 235/65R18 | 30.0 in | 9.3 in | +16.8% | 70.1 mph |
| 245/45R18 compared | 26.7 in | 9.6 in | +3.8% | 62.3 mph |
| 245/60R18 | 29.6 in | 9.6 in | +15.0% | 69.0 mph |
| 255/55R18 | 29.0 in | 10.0 in | +12.9% | 67.8 mph |
| 255/70R18 | 32.1 in | 10.0 in | +24.6% | 74.8 mph |
| 265/60R18 | 30.5 in | 10.4 in | +18.7% | 71.2 mph |
| 265/65R18 | 31.6 in | 10.4 in | +22.7% | 73.6 mph |
| 265/70R18 | 32.6 in | 10.4 in | +26.8% | 76.1 mph |
| 275/65R18 | 32.1 in | 10.8 in | +24.7% | 74.8 mph |
| 275/70R18 | 33.2 in | 10.8 in | +28.9% | 77.4 mph |
| 285/65R18 | 32.6 in | 11.2 in | +26.7% | 76.0 mph |
| 35x12.50R18 | 35.0 in | 12.5 in | +36.1% | 81.7 mph |
245/40R18 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 245/40R18 in inches?
About 25.7x9.6R18: 25.7 inches tall and 9.6 inches wide on a 18-inch wheel, with 3.9-inch sidewalls. Exactly, 18 + 2 × 245 mm × 0.40 ÷ 25.4 = 25.72 inches.
How many revolutions per mile does a 245/40R18 make?
784 by its diameter: 63,360 inches in a mile ÷ 80.8 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 LT245/40R18 the same size as P245/40R18?
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.