315/40R18 tire size
315/40R18 is a metric size: 27.9" tall, 12.4" wide, on a 18" rim — about a 28x12.50R18. The sidewall is 5.0" and the tire turns 722 times per mile.
315/40R18 specs
| Overall diameter (height) | 27.92" · 709 mm |
|---|---|
| Section width | 12.40" · 315 mm |
| Sidewall height | 4.96" · 126 mm (40% of width) |
| Rim diameter | 18" |
| Circumference | 87.72" · 2.228 m |
| Revolutions per mile | 722 (449 per km) |
| Inch (flotation) equivalent | 28x12.50R18 |
Equivalent sizes on a 18" rim
Sizes within ±5% of the overall diameter. Green rows are inside the usual ±3% limit for keeping the speedometer, ABS and gearing right; red rows are bigger changes that need clearance checks.
| Size | Diameter | Difference | Width | Speedo at 60 | |
|---|---|---|---|---|---|
| 235/60R18 common | 29.10" | +4.23% | -80 mm | 62.5 mph | calculate → |
| 245/45R18 common | 26.68" | -4.44% | -70 mm | 57.3 mph | calculate → |
| 235/50R18 common | 27.25" | -2.40% | -80 mm | 58.6 mph | calculate → |
| 235/55R18 common | 28.18" | +0.92% | -80 mm | 60.5 mph | calculate → |
| 225/60R18 common | 28.63" | +2.54% | -90 mm | 61.5 mph | calculate → |
| 225/50R18 common | 26.86" | -3.81% | -90 mm | 57.7 mph | calculate → |
| 225/55R18 common | 27.74" | -0.63% | -90 mm | 59.6 mph | calculate → |
| 255/55R18 common | 29.04" | +4.02% | -60 mm | 62.4 mph | calculate → |
| 245/50R18 common | 27.65" | -0.99% | -70 mm | 59.4 mph | calculate → |
| 255/45R18 common | 27.04" | -3.17% | -60 mm | 58.1 mph | calculate → |
| 215/55R18 common | 27.31" | -2.19% | -100 mm | 58.7 mph | calculate → |
| 275/40R18 common | 26.66" | -4.51% | -40 mm | 57.3 mph | calculate → |
| 245/55R18 | 28.61" | +2.47% | -70 mm | 61.5 mph | calculate → |
| 275/45R18 | 27.74" | -0.63% | -40 mm | 59.6 mph | calculate → |
| 265/45R18 | 27.39" | -1.90% | -50 mm | 58.9 mph | calculate → |
| 295/40R18 | 27.29" | -2.26% | -20 mm | 58.6 mph | calculate → |
| 285/40R18 | 26.98" | -3.38% | -30 mm | 58.0 mph | calculate → |
| 345/35R18 | 27.51" | -1.48% | +30 mm | 59.1 mph | calculate → |
| 295/45R18 | 28.45" | +1.90% | -20 mm | 61.1 mph | calculate → |
| 255/50R18 | 28.04" | +0.42% | -60 mm | 60.3 mph | calculate → |
| 155/90R18 | 28.98" | +3.81% | -160 mm | 62.3 mph | calculate → |
| 215/60R18 | 28.16" | +0.85% | -100 mm | 60.5 mph | calculate → |
| 305/40R18 | 27.61" | -1.13% | -10 mm | 59.3 mph | calculate → |
| 155/85R18 | 28.37" | +1.62% | -160 mm | 61.0 mph | calculate → |
| 305/45R18 | 28.81" | +3.17% | -10 mm | 61.9 mph | calculate → |
| 285/50R18 | 29.22" | +4.65% | -30 mm | 62.8 mph | calculate → |
| 28x12.00R18 | 28.00" | +0.28% | -10 mm | 60.2 mph | calculate → |
| 285/45R18 | 28.10" | +0.63% | -30 mm | 60.4 mph | calculate → |
| 145/85R18 | 27.70" | -0.78% | -170 mm | 59.5 mph | calculate → |
| 145/80R18 | 27.13" | -2.82% | -170 mm | 58.3 mph | calculate → |
| 165/70R18 | 27.09" | -2.96% | -150 mm | 58.2 mph | calculate → |
| 325/35R18 | 26.96" | -3.45% | +10 mm | 57.9 mph | calculate → |
| 155/70R18 | 26.54" | -4.94% | -160 mm | 57.0 mph | calculate → |
| 28x10.00R18 | 28.00" | +0.28% | -61 mm | 60.2 mph | calculate → |
| 205/60R18 | 27.69" | -0.85% | -110 mm | 59.5 mph | calculate → |
| 265/50R18 | 28.43" | +1.83% | -50 mm | 61.1 mph | calculate → |
| 195/60R18 | 27.21" | -2.54% | -120 mm | 58.5 mph | calculate → |
| 315/35R18 | 26.68" | -4.44% | 0 mm | 57.3 mph | calculate → |
Plus / minus sizing: 17" and 19" rims
Same overall height on a different rim. Check wheel width and clearance before switching.
| Size | Diameter | Difference | Width | Speedo at 60 | |
|---|---|---|---|---|---|
| 245/45R19 common | 27.68" | -0.86% | -70 mm | 59.5 mph | calculate → |
| 255/45R19 common | 28.04" | +0.41% | -60 mm | 60.2 mph | calculate → |
| 235/60R17 common | 28.10" | +0.65% | -80 mm | 60.4 mph | calculate → |
| 215/65R17 common | 28.00" | +0.30% | -100 mm | 60.2 mph | calculate → |
| 275/40R19 common | 27.66" | -0.93% | -40 mm | 59.4 mph | calculate → |
| 285/40R19 | 27.98" | +0.20% | -30 mm | 60.1 mph | calculate → |
| 155/90R17 | 27.98" | +0.23% | -160 mm | 60.1 mph | calculate → |
| 305/45R17 | 27.81" | -0.41% | -10 mm | 59.8 mph | calculate → |
| 255/55R17 | 28.04" | +0.44% | -60 mm | 60.3 mph | calculate → |
| 28x6.00R17 | 28.00" | +0.28% | -163 mm | 60.2 mph | calculate → |
| 275/50R17 | 27.83" | -0.34% | -40 mm | 59.8 mph | calculate → |
| 315/35R19 | 27.68" | -0.86% | 0 mm | 59.5 mph | calculate → |
| 345/40R17 | 27.87" | -0.20% | +30 mm | 59.9 mph | calculate → |
| 225/50R19 | 27.86" | -0.23% | -90 mm | 59.9 mph | calculate → |
| 145/80R19 | 28.13" | +0.76% | -170 mm | 60.5 mph | calculate → |
Try another size against 315/40R18
Questions
What size is 315/40R18 in inches?
315/40R18 is about 27.9" tall and 12.4" wide on a 18-inch rim — roughly a 28x12.50R18 in inch sizing.
What does 315/40R18 mean?
315 mm section width, sidewall 40% of the width (4.96"), radial construction, 18-inch rim.
What tire sizes are equivalent to 315/40R18?
On the same 18" rim, within 3% of the diameter: 28x10.00R18 (+0.28%), 28x12.00R18 (+0.28%), 255/50R18 (+0.42%), 225/55R18 (-0.63%), 275/45R18 (-0.63%), 285/45R18 (+0.63%).
How many revolutions per mile does a 315/40R18 tire make?
About 722 revolutions per mile (circumference 87.7").
How these numbers are computed
Diameter = rim + 2 × sidewall, sidewall = width × aspect ÷ 100, circumference = π × diameter, revolutions per mile = 63,360 ÷ circumference. Real tires differ by brand by a few tenths of an inch. Last reviewed October 14, 2026.