245/45R21 tire size
245/45R21 is a metric size: 29.7" tall, 9.6" wide, on a 21" rim — about a 29.5x9.50R21. The sidewall is 4.3" and the tire turns 679 times per mile.
245/45R21 specs
| Overall diameter (height) | 29.68" · 754 mm |
|---|---|
| Section width | 9.65" · 245 mm |
| Sidewall height | 4.34" · 110 mm (45% of width) |
| Rim diameter | 21" |
| Circumference | 93.25" · 2.368 m |
| Revolutions per mile | 679 (422 per km) |
| Inch (flotation) equivalent | 29.5x9.50R21 |
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" | -1.13% | +20 mm | 59.3 mph | compare → |
| 275/35R21 common | 28.58" | -3.71% | +30 mm | 57.8 mph | compare → |
| 295/35R21 | 29.13" | -1.86% | +50 mm | 58.9 mph | compare → |
| 275/45R21 | 30.74" | +3.58% | +30 mm | 62.1 mph | compare → |
| 255/40R21 | 29.03" | -2.19% | +10 mm | 58.7 mph | compare → |
| 265/35R21 | 28.30" | -4.64% | +20 mm | 57.2 mph | compare → |
| 295/40R21 | 30.29" | +2.06% | +50 mm | 61.2 mph | compare → |
| 285/45R21 | 31.10" | +4.78% | +40 mm | 62.9 mph | compare → |
| 285/40R21 | 29.98" | +0.99% | +40 mm | 60.6 mph | compare → |
| 265/45R21 | 30.39" | +2.39% | +20 mm | 61.4 mph | compare → |
| 325/30R21 | 28.68" | -3.38% | +80 mm | 58.0 mph | compare → |
| 275/40R21 | 29.66" | -0.07% | +30 mm | 60.0 mph | compare → |
| 285/35R21 | 28.85" | -2.79% | +40 mm | 58.3 mph | compare → |
| 315/30R21 | 28.44" | -4.18% | +70 mm | 57.5 mph | compare → |
| 315/35R21 | 29.68" | 0.00% | +70 mm | 60.0 mph | compare → |
| 245/40R21 | 28.72" | -3.25% | 0 mm | 58.1 mph | compare → |
| 305/30R21 | 28.20" | -4.97% | +60 mm | 57.0 mph | compare → |
| 315/40R21 | 30.92" | +4.18% | +70 mm | 62.5 mph | compare → |
| 255/45R21 | 30.04" | +1.19% | +10 mm | 60.7 mph | compare → |
| 255/50R21 | 31.04" | +4.58% | +10 mm | 62.7 mph | compare → |
| 235/50R21 | 30.25" | +1.92% | -10 mm | 61.2 mph | calculate → |
| 235/45R21 | 29.33" | -1.19% | -10 mm | 59.3 mph | calculate → |
| 305/35R21 | 29.41" | -0.93% | +60 mm | 59.4 mph | calculate → |
| 335/30R21 | 28.91" | -2.59% | +90 mm | 58.4 mph | calculate → |
| 345/30R21 | 29.15" | -1.79% | +100 mm | 58.9 mph | calculate → |
| 225/45R21 | 28.97" | -2.39% | -20 mm | 58.6 mph | calculate → |
| 305/40R21 | 30.61" | +3.12% | +60 mm | 61.9 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 | |
|---|---|---|---|---|---|
| 245/50R20 common | 29.65" | -0.12% | 0 mm | 59.9 mph | compare → |
| 275/45R20 common | 29.74" | +0.21% | +30 mm | 60.1 mph | compare → |
| 265/45R20 common | 29.39" | -0.98% | +20 mm | 59.4 mph | compare → |
| 285/35R22 | 29.85" | +0.58% | +40 mm | 60.4 mph | compare → |
| 275/35R22 | 29.58" | -0.34% | +30 mm | 59.8 mph | compare → |
| 305/40R20 | 29.61" | -0.25% | +60 mm | 59.8 mph | compare → |
| 315/30R22 | 29.44" | -0.81% | +70 mm | 59.5 mph | compare → |
| 325/30R22 | 29.68" | -0.01% | +80 mm | 60.0 mph | calculate → |
| 175/70R20 | 29.65" | -0.12% | -70 mm | 59.9 mph | calculate → |
Try another size against 245/45R21
Questions
What size is 245/45R21 in inches?
245/45R21 is about 29.7" tall and 9.6" wide on a 21-inch rim — roughly a 29.5x9.50R21 in inch sizing.
What does 245/45R21 mean?
245 mm section width, sidewall 45% of the width (4.34"), radial construction, 21-inch rim.
What tire sizes are equivalent to 245/45R21?
On the same 21" rim, within 3% of the diameter: 315/35R21 (0.00%), 275/40R21 (-0.07%), 305/35R21 (-0.93%), 285/40R21 (+0.99%), 265/40R21 (-1.13%), 255/45R21 (+1.19%).
How many revolutions per mile does a 245/45R21 tire make?
About 679 revolutions per mile (circumference 93.2").
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.