275/45R21 tire size
275/45R21 is a metric size: 30.7" tall, 10.8" wide, on a 21" rim — about a 30.5x11.00R21. The sidewall is 4.9" and the tire turns 656 times per mile.
275/45R21 specs
| Overall diameter (height) | 30.74" · 781 mm |
|---|---|
| Section width | 10.83" · 275 mm |
| Sidewall height | 4.87" · 124 mm (45% of width) |
| Rim diameter | 21" |
| Circumference | 96.59" · 2.453 m |
| Revolutions per mile | 656 (408 per km) |
| Inch (flotation) equivalent | 30.5x11.00R21 |
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 | |
|---|---|---|---|---|---|
| 265/40R21 common | 29.35" | -4.55% | -10 mm | 57.3 mph | compare → |
| 285/45R21 | 31.10" | +1.15% | +10 mm | 60.7 mph | compare → |
| 295/40R21 | 30.29" | -1.47% | +20 mm | 59.1 mph | compare → |
| 265/45R21 | 30.39" | -1.15% | -10 mm | 59.3 mph | compare → |
| 285/40R21 | 29.98" | -2.50% | +10 mm | 58.5 mph | compare → |
| 275/40R21 | 29.66" | -3.52% | 0 mm | 57.9 mph | compare → |
| 315/35R21 | 29.68" | -3.46% | +40 mm | 57.9 mph | compare → |
| 315/40R21 | 30.92" | +0.58% | +40 mm | 60.3 mph | compare → |
| 255/45R21 | 30.04" | -2.31% | -20 mm | 58.6 mph | compare → |
| 245/45R21 | 29.68" | -3.46% | -30 mm | 57.9 mph | compare → |
| 255/50R21 | 31.04" | +0.96% | -20 mm | 60.6 mph | compare → |
| 275/50R21 | 31.83" | +3.52% | 0 mm | 62.1 mph | compare → |
| 235/50R21 | 30.25" | -1.60% | -40 mm | 59.0 mph | calculate → |
| 235/45R21 | 29.33" | -4.61% | -40 mm | 57.2 mph | calculate → |
| 305/35R21 | 29.41" | -4.35% | +30 mm | 57.4 mph | calculate → |
| 305/40R21 | 30.61" | -0.45% | +30 mm | 59.7 mph | calculate → |
| 325/40R21 | 31.24" | +1.60% | +50 mm | 61.0 mph | calculate → |
| 315/45R21 | 32.16" | +4.61% | +40 mm | 62.8 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 | |
|---|---|---|---|---|---|
| 255/55R20 common | 31.04" | +0.97% | -20 mm | 60.6 mph | compare → |
| 275/50R20 common | 30.83" | +0.27% | 0 mm | 60.2 mph | compare → |
| 275/40R22 | 30.66" | -0.27% | 0 mm | 59.8 mph | compare → |
| 285/40R22 | 30.98" | +0.76% | +10 mm | 60.5 mph | compare → |
| 295/45R20 | 30.45" | -0.95% | +20 mm | 59.4 mph | compare → |
| 315/35R22 | 30.68" | -0.20% | +40 mm | 59.9 mph | compare → |
| 325/35R22 | 30.96" | +0.69% | +50 mm | 60.4 mph | compare → |
| 255/45R22 | 31.04" | +0.95% | -20 mm | 60.6 mph | calculate → |
| 305/45R20 | 30.81" | +0.20% | +30 mm | 60.1 mph | calculate → |
| 31x18.00R20 | 31.00" | +0.83% | +182 mm | 60.5 mph | calculate → |
Try another size against 275/45R21
Questions
What size is 275/45R21 in inches?
275/45R21 is about 30.7" tall and 10.8" wide on a 21-inch rim — roughly a 30.5x11.00R21 in inch sizing.
What does 275/45R21 mean?
275 mm section width, sidewall 45% of the width (4.87"), radial construction, 21-inch rim.
What tire sizes are equivalent to 275/45R21?
On the same 21" rim, within 3% of the diameter: 305/40R21 (-0.45%), 315/40R21 (+0.58%), 255/50R21 (+0.96%), 285/45R21 (+1.15%), 265/45R21 (-1.15%), 295/40R21 (-1.47%).
How many revolutions per mile does a 275/45R21 tire make?
About 656 revolutions per mile (circumference 96.6").
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.