A 275/55R20 tire measures about 31.9 inches tall, 10.8 inches wide, with a 5.95-inch sidewall, so most people round it to a 32-inch tire.
A 275/55R20 is a 20-inch radial tire whose printed size decodes into three real measurements, and getting them right is what keeps your speedometer honest and your rims safe. Below are the exact inches, the rim widths that fit, and the one number people get wrong.
What The Numbers On A 275/55R20 Actually Mean
Each part of the size code is a separate measurement: 275 is tire width in millimeters, 55 is the sidewall height as a percentage of that width, and R20 is a radial tire for a 20-inch wheel.
- 275 — section width in millimeters, which converts to about 10.8 inches.
- 55 — aspect ratio; the sidewall is 55% of 275 mm, or about 151.3 mm (roughly 5.95 inches).
- R — radial construction. Pirelli’s size guide lists R as standing for “Radial.”
- 20 — wheel diameter in inches; this tire mounts on a 20-inch rim only.
Height isn’t printed anywhere on the sidewall, so you calculate it: sidewall + wheel + sidewall. Two sidewalls of 5.95 inches plus the 20-inch wheel land at about 31.9 inches, and the circumference works out to roughly 100.2 inches, or about 632 revolutions per mile.
275/55R20 Dimensions In Inches
When you convert the metric sizing to inches and add the wheel diameter, a 275/55R20 comes out to about 31.9 inches tall and 10.8 inches wide — just shy of a true 32 inches.
| Measurement | Metric | In Inches |
|---|---|---|
| Section width | 275 mm | 10.8 in |
| Sidewall height | 151.3 mm | 5.95 in |
| Wheel diameter | 508 mm | 20 in |
| Overall diameter | — | 31.9 in |
| Circumference | — | 100.2 in |
| Revolutions per mile | — | About 632 |
| Approved wheel width | — | 7.5–9.5 in |
Tire-size reference charts list 7.5 to 9.5 inches as the approved wheel width range for this size, and that range appears on Continental’s own fitment listing for its TerrainContact A/T in LT275/55R20. Rim width matters as much as diameter here: a 275 on a 7.5-inch wheel sits taller and rounder than the same tire on a 9.5-inch wheel.
Load and speed ratings vary within the same nominal size. Continental lists 275/55R20 in 113T SL, 117H XL, and LT275/55R20 120/117S E constructions, all at 31.9 inches in diameter. Pick the rating your vehicle’s placard calls for, not just the size.
Is A 275/55R20 The Same As A 32-Inch Tire?
Not exactly. The calculated diameter is about 31.9 inches, so calling it a 32 is a convenience, not a measurement — the gap is roughly a tenth of an inch.
That rounding is why the size gets described as a 32-inch tire across fitment charts and owner discussions. It’s close enough for shopping shorthand and not close enough to treat as an exact match when you’re comparing clearance or calibrating a speedometer.
Two mix-ups cause most of the confusion. First, 275 is tire width in millimeters, not wheel diameter — the 20 at the end is the wheel. Second, a slightly taller or shorter diameter than your original equipment changes how fast the odometer and speedometer read. A tenth of an inch is minor; a full inch is not.
If you’re replacing worn rubber and want options that match this exact footprint, this rundown of tested 275/55R20 tires covers the common all-terrain and highway picks.
Before you buy, confirm three things: the wheel width falls inside 7.5–9.5 inches, the load and speed rating meets your vehicle’s requirement, and the new diameter is close to what came off. The 275/55R20 size reference confirms the 31.9-inch diameter and 7.5–9.5-inch rim range.
FAQs
How Tall Is A 275/55R20 In Inches?
It measures about 31.9 inches in overall diameter. That figure comes from adding two 5.95-inch sidewalls to the 20-inch wheel. Because it lands just under 32 inches, most charts and retailers round it up and call it a 32-inch tire.
Will A 275/55R20 Fit My Truck?
Fitment depends on your wheel width and vehicle clearance, not just the size code. The approved rim range is 7.5 to 9.5 inches. Check your door-jamb placard for the original tire size and load rating, and confirm clearance before buying.
Does A 275/55R20 Change My Speedometer?
It can, if the diameter differs from your original equipment. The circumference is about 100.2 inches, or roughly 632 revolutions per mile. A tenth of an inch of difference is negligible; a larger gap throws off speed and odometer readings and may need recalibration.
References & Sources
- Pirelli. “275/55 R20 Tire Size” Confirms R stands for Radial and the trailing digits give wheel diameter in inches.
- TireSize.com. “275/55R20 Tire Size” Source for the 31.9-inch diameter, 10.8-inch width, and 7.5–9.5-inch rim range.
- TireSize.com. “Continental TerrainContact A/T 275/55R20” Lists load and speed variants and confirms the 31.9-inch diameter.