245/40R18 tire size
245/40R18 is a metric size: 25.7" tall, 9.6" wide, on a 18" rim — about a 25.5x9.50R18. The sidewall is 3.9" and the tire turns 784 times per mile.
245/40R18 specs
| Overall diameter (height) | 25.72" · 653 mm |
|---|---|
| Section width | 9.65" · 245 mm |
| Sidewall height | 3.86" · 98 mm (40% of width) |
| Rim diameter | 18" |
| Circumference | 80.79" · 2.052 m |
| Revolutions per mile | 784 (487 per km) |
| Inch (flotation) equivalent | 25.5x9.50R18 |
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 | |
|---|---|---|---|---|---|
| 225/45R18 common | 25.97" | +1.00% | -20 mm | 60.6 mph | compare → |
| 225/40R18 common | 25.09" | -2.45% | -20 mm | 58.5 mph | compare → |
| 245/45R18 common | 26.68" | +3.75% | 0 mm | 62.3 mph | compare → |
| 235/45R18 common | 26.33" | +2.37% | -10 mm | 61.4 mph | compare → |
| 235/40R18 common | 25.40" | -1.22% | -10 mm | 59.3 mph | compare → |
| 225/50R18 common | 26.86" | +4.44% | -20 mm | 62.7 mph | compare → |
| 255/35R18 common | 25.03" | -2.68% | +10 mm | 58.4 mph | compare → |
| 255/40R18 common | 26.03" | +1.22% | +10 mm | 60.7 mph | compare → |
| 275/35R18 common | 25.58" | -0.54% | +30 mm | 59.7 mph | compare → |
| 265/35R18 common | 25.30" | -1.61% | +20 mm | 59.0 mph | compare → |
| 275/40R18 common | 26.66" | +3.67% | +30 mm | 62.2 mph | compare → |
| 215/45R18 common | 25.62" | -0.38% | -30 mm | 59.8 mph | compare → |
| 245/35R18 common | 24.75" | -3.75% | 0 mm | 57.7 mph | compare → |
| 215/40R18 | 24.77" | -3.67% | -30 mm | 57.8 mph | compare → |
| 285/35R18 | 25.85" | +0.54% | +40 mm | 60.3 mph | compare → |
| 265/40R18 | 26.35" | +2.45% | +20 mm | 61.5 mph | compare → |
| 295/30R18 | 24.97" | -2.91% | +50 mm | 58.3 mph | compare → |
| 315/30R18 | 25.44" | -1.07% | +70 mm | 59.4 mph | compare → |
| 285/30R18 | 24.73" | -3.83% | +40 mm | 57.7 mph | compare → |
| 295/35R18 | 26.13" | +1.61% | +50 mm | 61.0 mph | compare → |
| 205/40R18 | 24.46" | -4.90% | -40 mm | 57.1 mph | compare → |
| 335/30R18 | 25.91" | +0.77% | +90 mm | 60.5 mph | compare → |
| 215/50R18 | 26.46" | +2.91% | -30 mm | 61.7 mph | compare → |
| 285/40R18 | 26.98" | +4.90% | +40 mm | 62.9 mph | calculate → |
| 305/35R18 | 26.41" | +2.68% | +60 mm | 61.6 mph | calculate → |
| 235/35R18 | 24.48" | -4.82% | -10 mm | 57.1 mph | calculate → |
| 145/70R18 | 25.99" | +1.07% | -100 mm | 60.6 mph | calculate → |
| 26x12.00R18 | 26.00" | +1.10% | +60 mm | 60.7 mph | calculate → |
| 26x6.00R18 | 26.00" | +1.10% | -93 mm | 60.7 mph | calculate → |
| 26x8.00R18 | 26.00" | +1.10% | -42 mm | 60.7 mph | calculate → |
| 155/60R18 | 25.32" | -1.53% | -90 mm | 59.1 mph | calculate → |
| 305/30R18 | 25.20" | -1.99% | +60 mm | 58.8 mph | calculate → |
| 155/70R18 | 26.54" | +3.21% | -90 mm | 61.9 mph | calculate → |
| 325/35R18 | 26.96" | +4.82% | +80 mm | 62.9 mph | calculate → |
| 345/30R18 | 26.15" | +1.68% | +100 mm | 61.0 mph | calculate → |
| 205/45R18 | 25.26" | -1.76% | -40 mm | 58.9 mph | calculate → |
| 315/35R18 | 26.68" | +3.75% | +70 mm | 62.3 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 | |
|---|---|---|---|---|---|
| 225/50R17 common | 25.86" | +0.55% | -20 mm | 60.3 mph | compare → |
| 215/50R17 common | 25.46" | -0.98% | -30 mm | 59.4 mph | compare → |
| 245/45R17 common | 25.68" | -0.14% | 0 mm | 59.9 mph | compare → |
| 245/35R19 common | 25.75" | +0.14% | 0 mm | 60.1 mph | compare → |
| 235/35R19 common | 25.48" | -0.93% | -10 mm | 59.4 mph | compare → |
| 285/30R19 | 25.73" | +0.06% | +40 mm | 60.0 mph | compare → |
| 205/55R17 | 25.88" | +0.63% | -40 mm | 60.4 mph | compare → |
| 275/40R17 | 25.66" | -0.21% | +30 mm | 59.9 mph | compare → |
| 295/30R19 | 25.97" | +0.98% | +50 mm | 60.6 mph | compare → |
| 275/30R19 | 25.50" | -0.86% | +30 mm | 59.5 mph | compare → |
| 315/35R17 | 25.68" | -0.14% | +70 mm | 59.9 mph | compare → |
| 155/70R17 | 25.54" | -0.67% | -90 mm | 59.6 mph | calculate → |
| 175/65R17 | 25.96" | +0.93% | -70 mm | 60.6 mph | calculate → |
| 185/60R17 | 25.74" | +0.09% | -60 mm | 60.1 mph | calculate → |
Try another size against 245/40R18
Questions
What size is 245/40R18 in inches?
245/40R18 is about 25.7" tall and 9.6" wide on a 18-inch rim — roughly a 25.5x9.50R18 in inch sizing.
What does 245/40R18 mean?
245 mm section width, sidewall 40% of the width (3.86"), radial construction, 18-inch rim.
What tire sizes are equivalent to 245/40R18?
On the same 18" rim, within 3% of the diameter: 215/45R18 (-0.38%), 275/35R18 (-0.54%), 285/35R18 (+0.54%), 335/30R18 (+0.77%), 225/45R18 (+1.00%), 145/70R18 (+1.07%).
How many revolutions per mile does a 245/40R18 tire make?
About 784 revolutions per mile (circumference 80.8").
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.