305/25R21 tire size
305/25R21 is a metric size: 27.0" tall, 12.0" wide, on a 21" rim — about a 27x12.00R21. The sidewall is 3.0" and the tire turns 747 times per mile.
305/25R21 specs
| Overall diameter (height) | 27.00" · 686 mm |
|---|---|
| Section width | 12.01" · 305 mm |
| Sidewall height | 3.00" · 76 mm (25% of width) |
| Rim diameter | 21" |
| Circumference | 84.84" · 2.155 m |
| Revolutions per mile | 747 (464 per km) |
| Inch (flotation) equivalent | 27x12.00R21 |
Equivalent sizes on a 21" 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 | |
|---|---|---|---|---|---|
| 265/35R21 | 28.30" | +4.81% | -40 mm | 62.9 mph | calculate → |
| 245/35R21 | 27.75" | +2.77% | -60 mm | 61.7 mph | calculate → |
| 255/35R21 | 28.03" | +3.79% | -50 mm | 62.3 mph | calculate → |
| 295/30R21 | 27.97" | +3.57% | -10 mm | 62.1 mph | calculate → |
| 305/30R21 | 28.20" | +4.45% | 0 mm | 62.7 mph | calculate → |
| 285/30R21 | 27.73" | +2.70% | -20 mm | 61.6 mph | calculate → |
| 275/30R21 | 27.50" | +1.82% | -30 mm | 61.1 mph | calculate → |
| 255/30R21 | 27.02" | +0.07% | -50 mm | 60.0 mph | calculate → |
| 355/25R21 | 27.99" | +3.64% | +50 mm | 62.2 mph | calculate → |
| 295/25R21 | 26.81" | -0.73% | -10 mm | 59.6 mph | calculate → |
| 265/30R21 | 27.26" | +0.95% | -40 mm | 60.6 mph | calculate → |
| 325/25R21 | 27.40" | +1.46% | +20 mm | 60.9 mph | calculate → |
| 345/25R21 | 27.79" | +2.92% | +40 mm | 61.7 mph | calculate → |
| 245/30R21 | 26.79" | -0.80% | -60 mm | 59.5 mph | calculate → |
| 275/25R21 | 26.41" | -2.19% | -30 mm | 58.7 mph | calculate → |
Plus / minus sizing: 20" and 22" rims
Same overall height on a different rim. Check wheel width and clearance before switching.
| Size | Diameter | Difference | Width | Speedo at 60 | |
|---|---|---|---|---|---|
| 245/35R20 common | 26.75" | -0.93% | -60 mm | 59.4 mph | calculate → |
| 255/35R20 common | 27.03" | +0.09% | -50 mm | 60.1 mph | calculate → |
| 295/30R20 | 26.97" | -0.13% | -10 mm | 59.9 mph | calculate → |
| 305/30R20 | 27.20" | +0.74% | 0 mm | 60.4 mph | calculate → |
| 345/25R20 | 26.79" | -0.79% | +40 mm | 59.5 mph | calculate → |
| 225/40R20 | 27.09" | +0.31% | -80 mm | 60.2 mph | calculate → |
| 145/60R20 | 26.85" | -0.57% | -160 mm | 59.7 mph | calculate → |
Try another size against 305/25R21
Questions
What size is 305/25R21 in inches?
305/25R21 is about 27.0" tall and 12.0" wide on a 21-inch rim — roughly a 27x12.00R21 in inch sizing.
What does 305/25R21 mean?
305 mm section width, sidewall 25% of the width (3.00"), radial construction, 21-inch rim.
What tire sizes are equivalent to 305/25R21?
On the same 21" rim, within 3% of the diameter: 255/30R21 (+0.07%), 295/25R21 (-0.73%), 245/30R21 (-0.80%), 265/30R21 (+0.95%), 325/25R21 (+1.46%), 275/30R21 (+1.82%).
How many revolutions per mile does a 305/25R21 tire make?
About 747 revolutions per mile (circumference 84.8").
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.