305/30R18 tire size
305/30R18 is a metric size: 25.2" tall, 12.0" wide, on a 18" rim — about a 25x12.00R18. The sidewall is 3.6" and the tire turns 800 times per mile.
305/30R18 specs
| Overall diameter (height) | 25.20" · 640 mm |
|---|---|
| Section width | 12.01" · 305 mm |
| Sidewall height | 3.60" · 92 mm (30% of width) |
| Rim diameter | 18" |
| Circumference | 79.18" · 2.011 m |
| Revolutions per mile | 800 (497 per km) |
| Inch (flotation) equivalent | 25x12.00R18 |
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 | |
|---|---|---|---|---|---|
| 245/40R18 common | 25.72" | +2.03% | -60 mm | 61.2 mph | calculate → |
| 225/45R18 common | 25.97" | +3.05% | -80 mm | 61.8 mph | calculate → |
| 225/40R18 common | 25.09" | -0.47% | -80 mm | 59.7 mph | calculate → |
| 235/45R18 common | 26.33" | +4.45% | -70 mm | 62.7 mph | calculate → |
| 235/40R18 common | 25.40" | +0.78% | -70 mm | 60.5 mph | calculate → |
| 255/35R18 common | 25.03" | -0.70% | -50 mm | 59.6 mph | calculate → |
| 255/40R18 common | 26.03" | +3.28% | -50 mm | 62.0 mph | calculate → |
| 275/35R18 common | 25.58" | +1.48% | -30 mm | 60.9 mph | calculate → |
| 265/35R18 common | 25.30" | +0.39% | -40 mm | 60.2 mph | calculate → |
| 215/45R18 common | 25.62" | +1.64% | -90 mm | 61.0 mph | calculate → |
| 245/35R18 common | 24.75" | -1.80% | -60 mm | 58.9 mph | calculate → |
| 215/40R18 | 24.77" | -1.72% | -90 mm | 59.0 mph | calculate → |
| 285/35R18 | 25.85" | +2.58% | -20 mm | 61.5 mph | calculate → |
| 265/40R18 | 26.35" | +4.53% | -40 mm | 62.7 mph | calculate → |
| 295/30R18 | 24.97" | -0.94% | -10 mm | 59.4 mph | calculate → |
| 315/30R18 | 25.44" | +0.94% | +10 mm | 60.6 mph | calculate → |
| 285/30R18 | 24.73" | -1.87% | -20 mm | 58.9 mph | calculate → |
| 295/35R18 | 26.13" | +3.67% | -10 mm | 62.2 mph | calculate → |
| 205/40R18 | 24.46" | -2.97% | -100 mm | 58.2 mph | calculate → |
| 335/30R18 | 25.91" | +2.81% | +30 mm | 61.7 mph | calculate → |
| 215/50R18 | 26.46" | +5.00% | -90 mm | 63.0 mph | calculate → |
| 225/35R18 | 24.20" | -3.98% | -80 mm | 57.6 mph | calculate → |
| 305/35R18 | 26.41" | +4.76% | 0 mm | 62.9 mph | calculate → |
| 235/35R18 | 24.48" | -2.89% | -70 mm | 58.3 mph | calculate → |
| 155/60R18 | 25.32" | +0.47% | -150 mm | 60.3 mph | calculate → |
| 145/70R18 | 25.99" | +3.12% | -160 mm | 61.9 mph | calculate → |
| 26x12.00R18 | 26.00" | +3.16% | 0 mm | 61.9 mph | calculate → |
| 26x6.00R18 | 26.00" | +3.16% | -153 mm | 61.9 mph | calculate → |
| 26x8.00R18 | 26.00" | +3.16% | -102 mm | 61.9 mph | calculate → |
| 205/45R18 | 25.26" | +0.23% | -100 mm | 60.1 mph | calculate → |
| 345/30R18 | 26.15" | +3.75% | +40 mm | 62.2 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 | |
|---|---|---|---|---|---|
| 225/45R17 common | 24.97" | -0.92% | -80 mm | 59.4 mph | calculate → |
| 205/50R17 common | 25.07" | -0.53% | -100 mm | 59.7 mph | calculate → |
| 235/45R17 common | 25.33" | +0.48% | -70 mm | 60.3 mph | calculate → |
| 255/40R17 common | 25.03" | -0.69% | -50 mm | 59.6 mph | calculate → |
| 225/35R19 | 25.20" | -0.02% | -80 mm | 60.0 mph | calculate → |
| 255/30R19 | 25.02" | -0.72% | -50 mm | 59.6 mph | calculate → |
| 265/30R19 | 25.26" | +0.22% | -40 mm | 60.1 mph | calculate → |
| 265/40R17 | 25.35" | +0.56% | -40 mm | 60.3 mph | calculate → |
| 315/25R19 | 25.20" | -0.02% | +10 mm | 60.0 mph | calculate → |
| 295/35R17 | 25.13" | -0.30% | -10 mm | 59.8 mph | calculate → |
| 145/70R17 | 24.99" | -0.84% | -160 mm | 59.5 mph | calculate → |
Try another size against 305/30R18
Questions
What size is 305/30R18 in inches?
305/30R18 is about 25.2" tall and 12.0" wide on a 18-inch rim — roughly a 25x12.00R18 in inch sizing.
What does 305/30R18 mean?
305 mm section width, sidewall 30% of the width (3.60"), radial construction, 18-inch rim.
What tire sizes are equivalent to 305/30R18?
On the same 18" rim, within 3% of the diameter: 205/45R18 (+0.23%), 265/35R18 (+0.39%), 225/40R18 (-0.47%), 155/60R18 (+0.47%), 255/35R18 (-0.70%), 235/40R18 (+0.78%).
How many revolutions per mile does a 305/30R18 tire make?
About 800 revolutions per mile (circumference 79.2").
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.