315/45R21 tire size
315/45R21 is a metric size: 32.2" tall, 12.4" wide, on a 21" rim — about a 32x12.50R21. The sidewall is 5.6" and the tire turns 627 times per mile.
315/45R21 specs
| Overall diameter (height) | 32.16" · 817 mm |
|---|---|
| Section width | 12.40" · 315 mm |
| Sidewall height | 5.58" · 142 mm (45% of width) |
| Rim diameter | 21" |
| Circumference | 101.04" · 2.566 m |
| Revolutions per mile | 627 (390 per km) |
| Inch (flotation) equivalent | 32x12.50R21 |
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 | |
|---|---|---|---|---|---|
| 275/45R21 | 30.74" | -4.41% | -40 mm | 57.4 mph | calculate → |
| 285/45R21 | 31.10" | -3.31% | -30 mm | 58.0 mph | calculate → |
| 315/40R21 | 30.92" | -3.86% | 0 mm | 57.7 mph | calculate → |
| 255/50R21 | 31.04" | -3.49% | -60 mm | 57.9 mph | calculate → |
| 275/50R21 | 31.83" | -1.04% | -40 mm | 59.4 mph | calculate → |
| 275/55R21 | 32.91" | +2.33% | -40 mm | 61.4 mph | calculate → |
| 325/40R21 | 31.24" | -2.88% | +10 mm | 58.3 mph | calculate → |
| 305/40R21 | 30.61" | -4.84% | -10 mm | 57.1 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 | |
|---|---|---|---|---|---|
| 275/55R20 common | 31.91" | -0.78% | -40 mm | 59.5 mph | calculate → |
| 285/45R22 common | 32.10" | -0.20% | -30 mm | 59.9 mph | calculate → |
| 285/55R20 common | 32.34" | +0.56% | -30 mm | 60.3 mph | calculate → |
| 305/50R20 | 32.01" | -0.48% | -10 mm | 59.7 mph | calculate → |
| 255/60R20 | 32.05" | -0.36% | -60 mm | 59.8 mph | calculate → |
| 325/40R22 | 32.24" | +0.23% | +10 mm | 60.1 mph | calculate → |
| 265/50R22 | 32.43" | +0.84% | -50 mm | 60.5 mph | calculate → |
| 315/50R20 | 32.40" | +0.75% | 0 mm | 60.4 mph | calculate → |
Try another size against 315/45R21
Questions
What size is 315/45R21 in inches?
315/45R21 is about 32.2" tall and 12.4" wide on a 21-inch rim — roughly a 32x12.50R21 in inch sizing.
What does 315/45R21 mean?
315 mm section width, sidewall 45% of the width (5.58"), radial construction, 21-inch rim.
What tire sizes are equivalent to 315/45R21?
On the same 21" rim, within 3% of the diameter: 275/50R21 (-1.04%), 275/55R21 (+2.33%), 325/40R21 (-2.88%), 285/45R21 (-3.31%), 255/50R21 (-3.49%), 315/40R21 (-3.86%).
How many revolutions per mile does a 315/45R21 tire make?
About 627 revolutions per mile (circumference 101.0").
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.