305/30R20 tire size
305/30R20 is a metric size: 27.2" tall, 12.0" wide, on a 20" rim — about a 27x12.00R20. The sidewall is 3.6" and the tire turns 741 times per mile.
305/30R20 specs
| Overall diameter (height) | 27.20" · 691 mm |
|---|---|
| Section width | 12.01" · 305 mm |
| Sidewall height | 3.60" · 92 mm (30% of width) |
| Rim diameter | 20" |
| Circumference | 85.47" · 2.171 m |
| Revolutions per mile | 741 (461 per km) |
| Inch (flotation) equivalent | 27x12.00R20 |
Equivalent sizes on a 20" 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 | |
|---|---|---|---|---|---|
| 245/40R20 common | 27.72" | +1.88% | -60 mm | 61.1 mph | compare → |
| 245/35R20 common | 26.75" | -1.66% | -60 mm | 59.0 mph | compare → |
| 255/35R20 common | 27.03" | -0.65% | -50 mm | 59.6 mph | compare → |
| 275/35R20 common | 27.58" | +1.37% | -30 mm | 60.8 mph | compare → |
| 255/40R20 common | 28.03" | +3.04% | -50 mm | 61.8 mph | compare → |
| 285/35R20 common | 27.85" | +2.39% | -20 mm | 61.4 mph | compare → |
| 285/30R20 common | 26.73" | -1.74% | -20 mm | 59.0 mph | compare → |
| 275/30R20 common | 26.50" | -2.60% | -30 mm | 58.4 mph | compare → |
| 265/35R20 common | 27.30" | +0.36% | -40 mm | 60.2 mph | compare → |
| 235/35R20 | 26.48" | -2.68% | -70 mm | 58.4 mph | compare → |
| 295/30R20 | 26.97" | -0.87% | -10 mm | 59.5 mph | compare → |
| 295/35R20 | 28.13" | +3.40% | -10 mm | 62.0 mph | compare → |
| 305/35R20 | 28.41" | +4.41% | 0 mm | 62.6 mph | compare → |
| 265/30R20 | 26.26" | -3.47% | -40 mm | 57.9 mph | compare → |
| 255/30R20 | 26.02" | -4.34% | -50 mm | 57.4 mph | compare → |
| 235/45R20 | 28.33" | +4.12% | -70 mm | 62.5 mph | compare → |
| 225/35R20 | 26.20" | -3.69% | -80 mm | 57.8 mph | compare → |
| 265/40R20 | 28.35" | +4.20% | -40 mm | 62.5 mph | compare → |
| 335/25R20 | 26.59" | -2.24% | +30 mm | 58.7 mph | compare → |
| 315/30R20 | 27.44" | +0.87% | +10 mm | 60.5 mph | compare → |
| 305/25R20 | 26.00" | -4.41% | 0 mm | 57.4 mph | compare → |
| 235/40R20 | 27.40" | +0.72% | -70 mm | 60.4 mph | calculate → |
| 335/30R20 | 27.91" | +2.60% | +30 mm | 61.6 mph | calculate → |
| 325/25R20 | 26.40" | -2.97% | +20 mm | 58.2 mph | calculate → |
| 325/30R20 | 27.68" | +1.74% | +20 mm | 61.0 mph | calculate → |
| 345/30R20 | 28.15" | +3.47% | +40 mm | 62.1 mph | calculate → |
| 215/45R20 | 27.62" | +1.52% | -90 mm | 60.9 mph | calculate → |
| 345/25R20 | 26.79" | -1.52% | +40 mm | 59.1 mph | calculate → |
| 225/40R20 | 27.09" | -0.43% | -80 mm | 59.7 mph | calculate → |
| 195/50R20 | 27.68" | +1.74% | -110 mm | 61.0 mph | calculate → |
| 155/60R20 | 27.32" | +0.43% | -150 mm | 60.3 mph | calculate → |
| 145/65R20 | 27.42" | +0.80% | -160 mm | 60.5 mph | calculate → |
| 145/60R20 | 26.85" | -1.30% | -160 mm | 59.2 mph | calculate → |
| 175/55R20 | 27.58" | +1.37% | -130 mm | 60.8 mph | calculate → |
| 165/60R20 | 27.80" | +2.17% | -140 mm | 61.3 mph | calculate → |
| 155/65R20 | 27.93" | +2.68% | -150 mm | 61.6 mph | calculate → |
| 225/45R20 | 27.97" | +2.82% | -80 mm | 61.7 mph | calculate → |
| 315/25R20 | 26.20" | -3.69% | +10 mm | 57.8 mph | calculate → |
| 195/55R20 | 28.44" | +4.56% | -110 mm | 62.7 mph | calculate → |
Plus / minus sizing: 19" and 21" rims
Same overall height on a different rim. Check wheel width and clearance before switching.
| Size | Diameter | Difference | Width | Speedo at 60 | |
|---|---|---|---|---|---|
| 255/40R19 common | 27.03" | -0.64% | -50 mm | 59.6 mph | compare → |
| 225/45R19 common | 26.97" | -0.85% | -80 mm | 59.5 mph | compare → |
| 235/45R19 common | 27.33" | +0.45% | -70 mm | 60.3 mph | compare → |
| 265/40R19 | 27.35" | +0.52% | -40 mm | 60.3 mph | compare → |
| 295/35R19 | 27.13" | -0.27% | -10 mm | 59.8 mph | compare → |
| 345/30R19 | 27.15" | -0.20% | +40 mm | 59.9 mph | compare → |
| 255/30R21 | 27.02" | -0.67% | -50 mm | 59.6 mph | calculate → |
| 305/35R19 | 27.41" | +0.74% | 0 mm | 60.4 mph | calculate → |
| 355/30R19 | 27.39" | +0.67% | +50 mm | 60.4 mph | calculate → |
| 265/30R21 | 27.26" | +0.20% | -40 mm | 60.1 mph | calculate → |
| 325/25R21 | 27.40" | +0.71% | +20 mm | 60.4 mph | calculate → |
| 305/25R21 | 27.00" | -0.74% | 0 mm | 59.6 mph | calculate → |
| 215/50R19 | 27.46" | +0.96% | -90 mm | 60.6 mph | calculate → |
| 175/60R19 | 27.27" | +0.23% | -130 mm | 60.1 mph | calculate → |
Try another size against 305/30R20
Questions
What size is 305/30R20 in inches?
305/30R20 is about 27.2" tall and 12.0" wide on a 20-inch rim — roughly a 27x12.00R20 in inch sizing.
What does 305/30R20 mean?
305 mm section width, sidewall 30% of the width (3.60"), radial construction, 20-inch rim.
What tire sizes are equivalent to 305/30R20?
On the same 20" rim, within 3% of the diameter: 265/35R20 (+0.36%), 225/40R20 (-0.43%), 155/60R20 (+0.43%), 255/35R20 (-0.65%), 235/40R20 (+0.72%), 145/65R20 (+0.80%).
How many revolutions per mile does a 305/30R20 tire make?
About 741 revolutions per mile (circumference 85.5").
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.