245/40R21 tire size
245/40R21 is a metric size: 28.7" tall, 9.6" wide, on a 21" rim — about a 28.5x9.50R21. The sidewall is 3.9" and the tire turns 702 times per mile.
245/40R21 specs
| Overall diameter (height) | 28.72" · 729 mm |
|---|---|
| Section width | 9.65" · 245 mm |
| Sidewall height | 3.86" · 98 mm (40% of width) |
| Rim diameter | 21" |
| Circumference | 90.22" · 2.291 m |
| Revolutions per mile | 702 (436 per km) |
| Inch (flotation) equivalent | 28.5x9.50R21 |
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 | |
|---|---|---|---|---|---|
| 265/40R21 common | 29.35" | +2.19% | +20 mm | 61.3 mph | compare → |
| 275/35R21 common | 28.58" | -0.48% | +30 mm | 59.7 mph | compare → |
| 295/35R21 | 29.13" | +1.44% | +50 mm | 60.9 mph | compare → |
| 255/40R21 | 29.03" | +1.10% | +10 mm | 60.7 mph | compare → |
| 265/35R21 | 28.30" | -1.44% | +20 mm | 59.1 mph | compare → |
| 245/35R21 | 27.75" | -3.36% | 0 mm | 58.0 mph | compare → |
| 285/40R21 | 29.98" | +4.39% | +40 mm | 62.6 mph | compare → |
| 325/30R21 | 28.68" | -0.14% | +80 mm | 59.9 mph | compare → |
| 275/40R21 | 29.66" | +3.29% | +30 mm | 62.0 mph | compare → |
| 255/35R21 | 28.03" | -2.40% | +10 mm | 58.6 mph | compare → |
| 285/35R21 | 28.85" | +0.48% | +40 mm | 60.3 mph | compare → |
| 315/30R21 | 28.44" | -0.96% | +70 mm | 59.4 mph | compare → |
| 315/35R21 | 29.68" | +3.36% | +70 mm | 62.0 mph | compare → |
| 305/30R21 | 28.20" | -1.78% | +60 mm | 58.9 mph | compare → |
| 295/30R21 | 27.97" | -2.60% | +50 mm | 58.4 mph | compare → |
| 285/30R21 | 27.73" | -3.43% | +40 mm | 57.9 mph | compare → |
| 255/45R21 | 30.04" | +4.59% | +10 mm | 62.8 mph | compare → |
| 245/45R21 | 29.68" | +3.36% | 0 mm | 62.0 mph | compare → |
| 275/30R21 | 27.50" | -4.25% | +30 mm | 57.4 mph | compare → |
| 355/25R21 | 27.99" | -2.54% | +110 mm | 58.5 mph | calculate → |
| 235/45R21 | 29.33" | +2.13% | -10 mm | 61.3 mph | calculate → |
| 335/30R21 | 28.91" | +0.69% | +90 mm | 60.4 mph | calculate → |
| 305/35R21 | 29.41" | +2.40% | +60 mm | 61.4 mph | calculate → |
| 345/30R21 | 29.15" | +1.51% | +100 mm | 60.9 mph | calculate → |
| 225/45R21 | 28.97" | +0.89% | -20 mm | 60.5 mph | calculate → |
| 345/25R21 | 27.79" | -3.22% | +100 mm | 58.1 mph | calculate → |
| 325/25R21 | 27.40" | -4.59% | +80 mm | 57.2 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 | |
|---|---|---|---|---|---|
| 245/45R20 common | 28.68" | -0.12% | 0 mm | 59.9 mph | compare → |
| 275/40R20 common | 28.66" | -0.19% | +30 mm | 59.9 mph | compare → |
| 315/35R20 common | 28.68" | -0.12% | +70 mm | 59.9 mph | compare → |
| 285/40R20 | 28.98" | +0.90% | +40 mm | 60.5 mph | compare → |
| 285/30R22 | 28.73" | +0.05% | +40 mm | 60.0 mph | compare → |
| 295/30R22 | 28.97" | +0.88% | +50 mm | 60.5 mph | compare → |
| 335/25R22 | 28.59" | -0.43% | +90 mm | 59.7 mph | calculate → |
| 325/35R20 | 28.96" | +0.84% | +80 mm | 60.5 mph | calculate → |
| 275/30R22 | 28.50" | -0.77% | +30 mm | 59.5 mph | calculate → |
| 355/25R22 | 28.99" | +0.95% | +110 mm | 60.6 mph | calculate → |
| 29x15.00R20 | 29.00" | +0.99% | +136 mm | 60.6 mph | calculate → |
| 29x18.00R20 | 29.00" | +0.99% | +212 mm | 60.6 mph | calculate → |
| 195/55R20 | 28.44" | -0.95% | -50 mm | 59.4 mph | calculate → |
Try another size against 245/40R21
Questions
What size is 245/40R21 in inches?
245/40R21 is about 28.7" tall and 9.6" wide on a 21-inch rim — roughly a 28.5x9.50R21 in inch sizing.
What does 245/40R21 mean?
245 mm section width, sidewall 40% of the width (3.86"), radial construction, 21-inch rim.
What tire sizes are equivalent to 245/40R21?
On the same 21" rim, within 3% of the diameter: 325/30R21 (-0.14%), 275/35R21 (-0.48%), 285/35R21 (+0.48%), 335/30R21 (+0.69%), 225/45R21 (+0.89%), 315/30R21 (-0.96%).
How many revolutions per mile does a 245/40R21 tire make?
About 702 revolutions per mile (circumference 90.2").
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.