305/55R20 tire size in inches and millimeters
305/55R20 measures 33.21 inches in overall diameter, 12.01 inches in section width, with a 6.60 inch sidewall.
Every dimension
| Size | In inches | In millimetres |
|---|---|---|
| Overall diameter | 33.21 in | 843.5 mm |
| Section width | 12.01 in | 305 mm |
| Sidewall height | 6.60 in | 167.8 mm |
| Circumference | 104.33 in | 2,649.9 mm |
| Revolutions per mile | 607.3 per mile | 377.4 per km |
Sizes that fit the same wheel
These sizes share a 20 inch wheel diameter and sit within 3% of 305/55R20 in overall diameter, which is the range a swap stays inside without recalibrating anything.
The percentage difference in overall diameter is the speedometer error: a tire 2% taller makes an indicated 60 mph a true 61.2 mph. They are the same number, so it is shown once.
| Alternate size | Overall diameter | Difference (in) | Difference (%) | Width difference (in) |
|---|---|---|---|---|
| 335/50R20 | 33.19 | -0.02 | -0.06 | 1.18 |
| 225/75R20 | 33.29 | 0.08 | 0.24 | -3.15 |
| 195/85R20 | 33.05 | -0.16 | -0.47 | -4.33 |
| 255/65R20 | 33.05 | -0.16 | -0.47 | -1.97 |
| 275/60R20 | 32.99 | -0.22 | -0.65 | -1.18 |
| 235/70R20 | 32.95 | -0.26 | -0.77 | -2.76 |
| 285/60R20 | 33.46 | 0.26 | 0.77 | -0.79 |
| 205/80R20 | 32.91 | -0.30 | -0.89 | -3.94 |
| 245/70R20 | 33.50 | 0.30 | 0.89 | -2.36 |
| 215/80R20 | 33.54 | 0.33 | 1.01 | -3.54 |
| 265/65R20 | 33.56 | 0.35 | 1.07 | -1.57 |
| 345/50R20 | 33.58 | 0.37 | 1.13 | 1.57 |
| 325/50R20 | 32.80 | -0.41 | -1.24 | 0.79 |
| 295/55R20 | 32.78 | -0.43 | -1.30 | -0.39 |
| 315/55R20 | 33.64 | 0.43 | 1.30 | 0.39 |
| 205/85R20 | 33.72 | 0.51 | 1.54 | -3.94 |
| 215/75R20 | 32.70 | -0.51 | -1.54 | -3.54 |
| 355/45R20 | 32.58 | -0.63 | -1.90 | 1.97 |
| 235/75R20 | 33.88 | 0.67 | 2.02 | -2.76 |
| 245/65R20 | 32.54 | -0.67 | -2.02 | -2.36 |
| 265/60R20 | 32.52 | -0.69 | -2.07 | -1.57 |
| 295/60R20 | 33.94 | 0.73 | 2.19 | -0.39 |
| 355/50R20 | 33.98 | 0.77 | 2.31 | 1.97 |
| 225/70R20 | 32.40 | -0.81 | -2.43 | -3.15 |
| 315/50R20 | 32.40 | -0.81 | -2.43 | 0.39 |
| 185/85R20 | 32.38 | -0.83 | -2.49 | -4.72 |
| 255/70R20 | 34.06 | 0.85 | 2.55 | -1.97 |
| 275/65R20 | 34.07 | 0.87 | 2.61 | -1.18 |
| 285/55R20 | 32.34 | -0.87 | -2.61 | -0.79 |
| 325/55R20 | 34.07 | 0.87 | 2.61 | 0.79 |
| 195/80R20 | 32.28 | -0.93 | -2.79 | -4.33 |
| 225/80R20 | 34.17 | 0.96 | 2.90 | -3.15 |
| 345/45R20 | 32.22 | -0.98 | -2.96 | 1.57 |
How this is worked out
sidewall height in millimetres = section width × aspect ratio ÷ 100
overall diameter in inches = wheel diameter + (section width × aspect ratio × 2) ÷ 2540
section width in inches = section width in millimetres ÷ 25.4
circumference in inches = π × overall diameter
revolutions per mile = 63360 ÷ circumference in inches
The divisor is 2540, not the 2550 some converters publish. Two sidewalls in inches are 2 × width × aspect ÷ (100 × 25.4), and the rounding costs about 0.07 inches at 34 inches.
For 305/55R20: the sidewall is 167.8 millimetres, two of them are 13.21 inches, and adding the 20 inch wheel gives 33.21 inches overall.
Questions
What size is 305/55R20 in inches?
33.21 inches in overall diameter, 12.01 inches in section width, with a 6.60 inch sidewall.
How tall is a 305/55R20 tire?
33.21 inches, which is 843.5 millimetres.
What do the numbers in 305/55R20 mean?
305 is the section width in millimetres, 55 is the sidewall height as a percentage of that width, and 20 is the wheel diameter in inches. Overall diameter is the wheel diameter plus two sidewalls: 33.21 inches.
Does 305/55R20 fit a 20-inch wheel?
Yes — the 20 in a metric tire size *is* the wheel diameter, so 305/55R20 is made for a 20 inch wheel. Rim width is a separate question the sidewall code does not answer.
What tire sizes are equivalent to 305/55R20?
335/50R20, 225/75R20, 195/85R20 are the closest by overall diameter, all on the same 20 inch wheel.
Fitting a size is not only a matter of diameter. Rim width, load rating, speed rating and clearance all decide whether a size works on a given vehicle, and none of them can be read off the sidewall code alone.