305/40R18 tire size
305/40R18 is a metric size: 27.6" tall, 12.0" wide, on a 18" rim — about a 27.5x12.00R18. The sidewall is 4.8" and the tire turns 731 times per mile.
305/40R18 specs
| Overall diameter (height) | 27.61" · 701 mm |
|---|---|
| Section width | 12.01" · 305 mm |
| Sidewall height | 4.80" · 122 mm (40% of width) |
| Rim diameter | 18" |
| Circumference | 86.73" · 2.203 m |
| Revolutions per mile | 731 (454 per km) |
| Inch (flotation) equivalent | 27.5x12.00R18 |
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 | |
|---|---|---|---|---|---|
| 245/45R18 common | 26.68" | -3.35% | -60 mm | 58.0 mph | calculate → |
| 235/50R18 common | 27.25" | -1.28% | -70 mm | 59.2 mph | calculate → |
| 235/55R18 common | 28.18" | +2.07% | -70 mm | 61.2 mph | calculate → |
| 235/45R18 common | 26.33" | -4.63% | -70 mm | 57.2 mph | calculate → |
| 225/60R18 common | 28.63" | +3.71% | -80 mm | 62.2 mph | calculate → |
| 225/50R18 common | 26.86" | -2.71% | -80 mm | 58.4 mph | calculate → |
| 225/55R18 common | 27.74" | +0.50% | -80 mm | 60.3 mph | calculate → |
| 245/50R18 common | 27.65" | +0.14% | -60 mm | 60.1 mph | calculate → |
| 255/45R18 common | 27.04" | -2.07% | -50 mm | 58.8 mph | calculate → |
| 215/55R18 common | 27.31" | -1.07% | -90 mm | 59.4 mph | calculate → |
| 275/40R18 common | 26.66" | -3.42% | -30 mm | 57.9 mph | calculate → |
| 245/55R18 | 28.61" | +3.64% | -60 mm | 62.2 mph | calculate → |
| 265/40R18 | 26.35" | -4.56% | -40 mm | 57.3 mph | calculate → |
| 275/45R18 | 27.74" | +0.50% | -30 mm | 60.3 mph | calculate → |
| 215/50R18 | 26.46" | -4.14% | -90 mm | 57.5 mph | calculate → |
| 265/45R18 | 27.39" | -0.78% | -40 mm | 59.5 mph | calculate → |
| 295/40R18 | 27.29" | -1.14% | -10 mm | 59.3 mph | calculate → |
| 285/40R18 | 26.98" | -2.28% | -20 mm | 58.6 mph | calculate → |
| 345/35R18 | 27.51" | -0.36% | +40 mm | 59.8 mph | calculate → |
| 305/35R18 | 26.41" | -4.35% | 0 mm | 57.4 mph | calculate → |
| 295/45R18 | 28.45" | +3.07% | -10 mm | 61.8 mph | calculate → |
| 255/50R18 | 28.04" | +1.57% | -50 mm | 60.9 mph | calculate → |
| 315/40R18 | 27.92" | +1.14% | +10 mm | 60.7 mph | calculate → |
| 155/90R18 | 28.98" | +4.99% | -150 mm | 63.0 mph | calculate → |
| 215/60R18 | 28.16" | +2.00% | -90 mm | 61.2 mph | calculate → |
| 155/85R18 | 28.37" | +2.78% | -150 mm | 61.7 mph | calculate → |
| 305/45R18 | 28.81" | +4.35% | 0 mm | 62.6 mph | calculate → |
| 145/85R18 | 27.70" | +0.36% | -160 mm | 60.2 mph | calculate → |
| 28x12.00R18 | 28.00" | +1.43% | 0 mm | 60.9 mph | calculate → |
| 145/80R18 | 27.13" | -1.71% | -160 mm | 59.0 mph | calculate → |
| 285/45R18 | 28.10" | +1.78% | -20 mm | 61.1 mph | calculate → |
| 165/70R18 | 27.09" | -1.85% | -140 mm | 58.9 mph | calculate → |
| 325/35R18 | 26.96" | -2.35% | +20 mm | 58.6 mph | calculate → |
| 155/70R18 | 26.54" | -3.85% | -150 mm | 57.7 mph | calculate → |
| 205/60R18 | 27.69" | +0.29% | -100 mm | 60.2 mph | calculate → |
| 195/60R18 | 27.21" | -1.43% | -110 mm | 59.1 mph | calculate → |
| 28x10.00R18 | 28.00" | +1.43% | -51 mm | 60.9 mph | calculate → |
| 265/50R18 | 28.43" | +2.99% | -40 mm | 61.8 mph | calculate → |
| 315/35R18 | 26.68" | -3.35% | +10 mm | 58.0 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" | +0.27% | -60 mm | 60.2 mph | calculate → |
| 225/60R17 common | 27.63" | +0.09% | -80 mm | 60.1 mph | calculate → |
| 275/40R19 common | 27.66" | +0.20% | -30 mm | 60.1 mph | calculate → |
| 265/40R19 | 27.35" | -0.94% | -40 mm | 59.4 mph | calculate → |
| 245/55R17 | 27.61" | +0.01% | -60 mm | 60.0 mph | calculate → |
| 305/35R19 | 27.41" | -0.73% | 0 mm | 59.6 mph | calculate → |
| 155/70R19 | 27.54" | -0.23% | -150 mm | 59.9 mph | calculate → |
| 355/30R19 | 27.39" | -0.80% | +50 mm | 59.5 mph | calculate → |
| 215/50R19 | 27.46" | -0.51% | -90 mm | 59.7 mph | calculate → |
| 305/45R17 | 27.81" | +0.73% | 0 mm | 60.4 mph | calculate → |
| 165/80R17 | 27.39" | -0.77% | -140 mm | 59.5 mph | calculate → |
| 315/35R19 | 27.68" | +0.27% | +10 mm | 60.2 mph | calculate → |
| 275/50R17 | 27.83" | +0.80% | -30 mm | 60.5 mph | calculate → |
| 205/65R17 | 27.49" | -0.41% | -100 mm | 59.8 mph | calculate → |
| 225/50R19 | 27.86" | +0.91% | -80 mm | 60.5 mph | calculate → |
| 345/40R17 | 27.87" | +0.94% | +40 mm | 60.6 mph | calculate → |
Try another size against 305/40R18
Questions
What size is 305/40R18 in inches?
305/40R18 is about 27.6" tall and 12.0" wide on a 18-inch rim — roughly a 27.5x12.00R18 in inch sizing.
What does 305/40R18 mean?
305 mm section width, sidewall 40% of the width (4.80"), radial construction, 18-inch rim.
What tire sizes are equivalent to 305/40R18?
On the same 18" rim, within 3% of the diameter: 245/50R18 (+0.14%), 205/60R18 (+0.29%), 145/85R18 (+0.36%), 345/35R18 (-0.36%), 225/55R18 (+0.50%), 275/45R18 (+0.50%).
How many revolutions per mile does a 305/40R18 tire make?
About 731 revolutions per mile (circumference 86.7").
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.