305/55R20 tire size in inches
A 305/55R20 tire is 33.21 inches tall and 12.01 inches wide on a 20-inch rim. These are nominal dimensions from the official sizing formula.
| Dimension | 305/55R20 | This size vs yours | |
|---|---|---|---|
| Overall diameter UN R30 §6.1.2.1 | 33.21 in 843.5 mm | ||
| Section width UN R30 §6.1.2.1 | 12.01 in 305.0 mm | ||
| Sidewall height UN R30 §6.1.2.1 | 6.60 in 167.8 mm | ||
| Rim diameter Marked on the tire | 20 in | ||
| Circumference From diameter | 104.33 in | ||
| Revolutions per mile From diameter | 607 | ||
| Allowed real diameter UN R30 §6.1.5 | 32.81–33.74 in |
Is 305/55R20 a 33-inch tire?
Yes. At 33.21 inches tall, 305/55R20 is commonly called a 33-inch tire. Inch-class names round to the nearest inch; the true nominal height is 33.21 in, and a new tire may legally measure between 32.81 and 33.74 in.
Speedometer change
Example: if your speedometer is calibrated for 275/60R20 and you fit 305/55R20, the tire is +0.7% in diameter, so your true speed differs from the reading as shown below. Enter your current size above to see your own figures.
| Reading | True speed | Difference |
|---|---|---|
| 30 mph | 30.2 mph | +0.2 mph |
| 45 mph | 45.3 mph | +0.3 mph |
| 55 mph | 55.4 mph | +0.4 mph |
| 60 mph | 60.4 mph | +0.4 mph |
| 70 mph | 70.5 mph | +0.5 mph |
| 80 mph | 80.5 mph | +0.5 mph |
Sizes within 3% of 305/55R20
These sizes are within 3% of the diameter of 305/55R20. The 3% figure is a rule of thumb, not a regulation and not a fitment check: wheel width, offset, suspension and body clearance decide what fits. See changing tire size.
| Size | Diameter (in) | Width (in) | Change | ±3% | Ride height (in) |
|---|---|---|---|---|---|
| 285/55R20 | 32.34 | 11.22 | −2.6% | −0.43 | |
| 265/60R20 | 32.52 | 10.43 | −2.1% | −0.34 | |
| 33x12.50R15 | 32.52 | 12.52 | −2.1% | −0.34 | |
| 285/65R18 | 32.59 | 11.22 | −1.9% | −0.31 | |
| 265/70R18 | 32.61 | 10.43 | −1.8% | −0.30 | |
| 285/70R17 | 32.71 | 11.22 | −1.5% | −0.25 | |
| 295/55R20 | 32.78 | 11.61 | −1.3% | −0.22 | |
| 305/70R16 | 32.81 | 12.01 | −1.2% | −0.20 | |
| 285/75R16 | 32.83 | 11.22 | −1.1% | −0.19 | |
| 275/60R20 | 32.99 | 10.83 | −0.7% | −0.11 | |
| 33x12.50R17 | 33.00 | 12.50 | −0.6% | −0.10 | |
| 255/85R16 | 33.07 | 10.04 | −0.4% | −0.07 | |
| 275/70R18 | 33.16 | 10.83 | −0.2% | −0.03 | |
| 305/55R20 | 33.21 | 12.01 | — | — | |
| 295/70R17 | 33.26 | 11.61 | +0.2% | +0.03 | |
| 295/75R16 | 33.42 | 11.61 | +0.6% | +0.11 | |
| 285/60R20 | 33.46 | 11.22 | +0.8% | +0.13 | |
| 285/70R18 | 33.71 | 11.22 | +1.5% | +0.25 | |
| 305/70R17 | 33.81 | 12.01 | +1.8% | +0.30 | |
| 285/75R17 | 33.83 | 11.22 | +1.9% | +0.31 | |
| 295/60R20 | 33.94 | 11.61 | +2.2% | +0.36 | |
| 275/65R20 | 34.07 | 10.83 | +2.6% | +0.43 |
Inch equivalent of 305/55R20
In inch terms, 305/55R20 is about 33.2x12.0R20: 33.2 in tall and 12.0 in wide, a 33-inch tire.
| Inch size | Diameter (in) | Change | Width (in) | Dimensions from |
|---|---|---|---|---|
| 33x12.50R20 | 33.00 | −0.6% | 12.50 | numbers in the size |
| 33x12.50R17 | 33.00 | −0.6% | 12.50 | numbers in the size |
| 33x12.50R18 | 33.00 | −0.6% | 12.50 | numbers in the size |
How 305/55R20 is calculated
305 mm section width × 55% aspect ratio = 167.8 mm sidewall (6.60 in).
Overall diameter = rim + 2 × sidewall = 20 in + 2 × 6.60 in = 33.21 in.
Formula: UN Regulation No. 30 §2.15 and §6.1.2.1 (passenger) and UN Regulation No. 54 §6.1.2.1 (light truck). Revolutions per mile = 63,360 ÷ circumference. Full sources are listed at the end of this page.
Questions about 305/55R20
- How tall is a 305/55R20 tire?
- 33.21 inches (843.5 mm) nominal. A new tire may measure from 32.81 to 33.74 in under the official tolerance; the maker's specification gives the figure for a specific tire.
- How wide is a 305/55R20 tire?
- 12.01 inches (305.0 mm) section width. Overall width can be slightly larger; for passenger tires, US rule FMVSS 139 allows 7% over the specified width (or 10 mm, if larger, for some pressure classes).
- How many revolutions per mile does 305/55R20 make?
- About 607 nominal, from a circumference of 104.33 in. Tire makers publish measured revolutions per mile for each tire.
- Will 305/55R20 fit my vehicle?
- This page can't tell you. Check the tire size on your door-jamb placard, then confirm wheel width, offset and clearance with the tire or vehicle maker.
Related
- All 20" sizes
- 275/60R20 vs 305/55R20
- 305/55R20 vs 275/65R20
- 305/55R20 vs 285/60R20
- 285/55R20 vs 305/55R20
- 295/55R20 vs 305/55R20
- 265/60R20 vs 305/55R20
- Tire size chart
- Wheel offset calculator
- Re-gear calculator
- Plus-size calculator
Printed from https://tiresizecalc.net/size/305-55r20/. Figures as published on 2026-11-01. The full working and the official sources are on that page.
Sources
This size is listed by the manufacturer: Goodyear Wrangler DuraTrac RT-LT, checked on the manufacturer's site on 2026-11-01. The size page shows nominal figures, not that product's measurements.
- UN Regulation No. 30 - Uniform provisions concerning the approval of pneumatic tyres for motor vehicles and their trailers (Revision 3). United Nations Economic Commission for Europe (UNECE). E/ECE/324 E/ECE/TRANS/505 Rev.1/Add.29/Rev.3. 2007-03-29. Para 2.15 and 6.1.2.1: aspect ratio and outer diameter, D = d + 2H. Retrieved 2026-11-01.
- UN Regulation No. 54 - Uniform provisions concerning the approval of pneumatic tyres for commercial vehicles and their trailers (Revision 2). United Nations Economic Commission for Europe (UNECE). E/ECE/324 E/ECE/TRANS/505 Rev.1/Add.53/Rev.2. 2004-04-16. Para 6.1.2.1: the same formula for light truck tires. Retrieved 2026-11-01.
- UN Regulation No. 30 - Uniform provisions concerning the approval of pneumatic tyres for motor vehicles and their trailers (Revision 3). United Nations Economic Commission for Europe (UNECE). E/ECE/324 E/ECE/TRANS/505 Rev.1/Add.29/Rev.3. 2007-03-29. Para 6.1.5: allowed outer diameter, Dmin = d + 2H x 0.97, Dmax = d + 2H x 1.04. Retrieved 2026-11-01.
- UN Regulation No. 54 - Uniform provisions concerning the approval of pneumatic tyres for commercial vehicles and their trailers (Revision 2). United Nations Economic Commission for Europe (UNECE). E/ECE/324 E/ECE/TRANS/505 Rev.1/Add.53/Rev.2. 2004-04-16. Annex 5 Part II Table B: design outer diameter and section width of 33x12.50R15LT. Retrieved 2026-11-01.
- UN Regulation No. 54 - Uniform provisions concerning the approval of pneumatic tyres for commercial vehicles and their trailers (Revision 2). United Nations Economic Commission for Europe (UNECE). E/ECE/324 E/ECE/TRANS/505 Rev.1/Add.53/Rev.2. 2004-04-16. Para 6.1.5.1, 6.1.5.3.1 and Table B note 2: allowed outer diameter for table sizes. Retrieved 2026-11-01.
- Computed by tiresizecalc.net from the cited formula. Sri Murugan Systems. Not in UN R54 Annex 5 Table B: diameter and width of 33x12.50R17 are the numbers in the size. Retrieved 2026-11-01.
- Computed by tiresizecalc.net from the cited formula. Sri Murugan Systems. Circumference = pi x diameter; revolutions per mile = 63,360 / circumference; 1 in = 25.4 mm exactly. Retrieved 2026-11-01.
- 49 CFR 571.139 - Standard No. 139; New pneumatic radial tires for light vehicles. National Highway Traffic Safety Administration (NHTSA), Code of Federal Regulations (eCFR). 49 CFR 571.139. eCFR up to date as of 2026-10-15. S6.1.2: passenger tire width up to 7 percent (or 10 mm) over the specified width. Retrieved 2026-11-01.
- 49 CFR 571.110 - Standard No. 110; Tire selection and rims for motor vehicles with a GVWR of 4,536 kilograms (10,000 pounds) or less. National Highway Traffic Safety Administration (NHTSA), Code of Federal Regulations, annual edition (GovInfo). 2006-10-01. S4.3: the door placard shows the original tire size. Retrieved 2026-11-01.
Last reviewed 2026-11-01. The full source list, with dates and file checksums, is in How the numbers are calculated. To report an error, email contactus@tiresizecalc.net.