305/45R20 tire size
305/45R20 is a metric size: 30.8" tall, 12.0" wide, on a 20" rim — about a 31x12.00R20. The sidewall is 5.4" and the tire turns 655 times per mile.
305/45R20 specs
| Overall diameter (height) | 30.81" · 783 mm |
|---|---|
| Section width | 12.01" · 305 mm |
| Sidewall height | 5.40" · 137 mm (45% of width) |
| Rim diameter | 20" |
| Circumference | 96.78" · 2.458 m |
| Revolutions per mile | 655 (407 per km) |
| Inch (flotation) equivalent | 31x12.00R20 |
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 | |
|---|---|---|---|---|---|
| 275/55R20 common | 31.91" | +3.58% | -30 mm | 62.1 mph | calculate → |
| 255/50R20 common | 30.04" | -2.49% | -50 mm | 58.5 mph | calculate → |
| 265/50R20 common | 30.43" | -1.21% | -40 mm | 59.3 mph | calculate → |
| 245/50R20 common | 29.65" | -3.77% | -60 mm | 57.7 mph | calculate → |
| 275/45R20 common | 29.74" | -3.45% | -30 mm | 57.9 mph | calculate → |
| 255/55R20 common | 31.04" | +0.77% | -50 mm | 60.5 mph | calculate → |
| 235/55R20 common | 30.18" | -2.04% | -70 mm | 58.8 mph | calculate → |
| 265/45R20 common | 29.39" | -4.60% | -40 mm | 57.2 mph | calculate → |
| 285/55R20 common | 32.34" | +4.98% | -20 mm | 63.0 mph | calculate → |
| 275/50R20 common | 30.83" | +0.06% | -30 mm | 60.0 mph | calculate → |
| 295/40R20 | 29.29" | -4.92% | -10 mm | 57.0 mph | calculate → |
| 285/50R20 | 31.22" | +1.34% | -20 mm | 60.8 mph | calculate → |
| 245/60R20 | 31.57" | +2.49% | -60 mm | 61.5 mph | calculate → |
| 285/45R20 | 30.10" | -2.30% | -20 mm | 58.6 mph | calculate → |
| 305/50R20 | 32.01" | +3.90% | 0 mm | 62.3 mph | calculate → |
| 295/45R20 | 30.45" | -1.15% | -10 mm | 59.3 mph | calculate → |
| 305/40R20 | 29.61" | -3.90% | 0 mm | 57.7 mph | calculate → |
| 255/60R20 | 32.05" | +4.03% | -50 mm | 62.4 mph | calculate → |
| 235/60R20 | 31.10" | +0.96% | -70 mm | 60.6 mph | calculate → |
| 31x18.00R20 | 31.00" | +0.63% | +152 mm | 60.4 mph | calculate → |
| 265/55R20 | 31.48" | +2.17% | -40 mm | 61.3 mph | calculate → |
| 295/50R20 | 31.61" | +2.62% | -10 mm | 61.6 mph | calculate → |
| 175/70R20 | 29.65" | -3.77% | -130 mm | 57.7 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 | |
|---|---|---|---|---|---|
| 255/60R19 common | 31.05" | +0.78% | -50 mm | 60.5 mph | calculate → |
| 275/45R21 | 30.74" | -0.20% | -30 mm | 59.9 mph | calculate → |
| 285/45R21 | 31.10" | +0.95% | -20 mm | 60.6 mph | calculate → |
| 275/55R19 | 30.91" | +0.33% | -30 mm | 60.2 mph | calculate → |
| 315/40R21 | 30.92" | +0.37% | +10 mm | 60.2 mph | calculate → |
| 255/50R21 | 31.04" | +0.75% | -50 mm | 60.5 mph | calculate → |
| 235/65R19 | 31.03" | +0.72% | -70 mm | 60.4 mph | calculate → |
| 305/40R21 | 30.61" | -0.65% | 0 mm | 59.6 mph | calculate → |
| 165/90R19 | 30.69" | -0.37% | -140 mm | 59.8 mph | calculate → |
Try another size against 305/45R20
Questions
What size is 305/45R20 in inches?
305/45R20 is about 30.8" tall and 12.0" wide on a 20-inch rim — roughly a 31x12.00R20 in inch sizing.
What does 305/45R20 mean?
305 mm section width, sidewall 45% of the width (5.40"), radial construction, 20-inch rim.
What tire sizes are equivalent to 305/45R20?
On the same 20" rim, within 3% of the diameter: 275/50R20 (+0.06%), 31x18.00R20 (+0.63%), 255/55R20 (+0.77%), 235/60R20 (+0.96%), 295/45R20 (-1.15%), 265/50R20 (-1.21%).
How many revolutions per mile does a 305/45R20 tire make?
About 655 revolutions per mile (circumference 96.8").
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.