305/55R20 Tire Size in Inches | The 33-Inch Conversion

A 305/55R20 tire measures about 33.2 inches in diameter, 12.0 inches wide, on a 20-inch wheel.

Before you pick a lift kit or worry about fender clearance, you need the 305/55R20 tire size in inches: 33.2 by 12.0 by 20. That’s a 33-inch-tall tire with a section width of about 12 inches, a 6.6-inch sidewall, and a 20-inch wheel opening. Together those numbers settle the clearance, speedometer, and wheel-width questions that come up before almost every purchase.

305/55R20 In Inches: The Full Spec Sheet

The 305/55R20 works out to a 33.2-inch overall diameter, a 12.0-inch section width, and a 6.6-inch sidewall on a 20-inch rim. Diameter matters most for fender clearance; width matters for wheel choice. Those are the standard published figures across the major size charts, and the table below condenses every measurement into one place.

The same math produces a circumference of about 104.3 inches and roughly 608 revolutions per mile — the numbers to save if you’re estimating speedometer change after a tire swap. TireSize.com’s 305/55R20 size chart keeps the full list of specs with the underlying calculations. Real-world measurements vary slightly by brand and tread design, so treat these figures as the standard baseline rather than a promise every manufacturer matches exactly.

What Does The 305/55R20 Size Code Mean?

Each part of the code names a physical dimension: 305 is the section width in millimeters, 55 is the aspect ratio, and R20 means a radial tire built for a 20-inch wheel.

The width converts directly: 305 millimeters equals 12.0 inches. The aspect ratio says the sidewall height is 55 percent of that width, which comes to about 6.6 inches. Add two sidewalls to the wheel diameter — 6.6 plus 6.6 plus 20 — and you land on the 33.2-inch overall diameter. The only math that trips people up is the unit swap: divide millimeters by 25.4 to get inches, so 305 divided by 25.4 works out to 12.0. The same three-part logic applies to every metric tire size, so once you can read 305/55R20, you can read any code on a sidewall.

Will A 305/55R20 Fit Your Truck Or SUV?

Fitment depends on more than the size alone. Wheel width, suspension clearance, and load ratings decide whether a 305/55R20 actually works on your vehicle.

This is a light-truck-style size, common on full-size trucks and SUVs, and most 305/55R20 tires are approved for wheels between 8.5 and 11 inches wide. Published specs vary a little by brand — TireSize.com’s listings for the BFGoodrich All-Terrain T/A KO2 and the Toyo Open Country A/T III both show the 33.2-inch diameter, with section width ranging from about 12.0 to 12.4 inches depending on the model. In floatation sizing, this is the metric equivalent of a 33×12.50R20.

Before ordering, match the tire’s load index, speed rating, and load range to what your vehicle requires. Full-size trucks and SUVs can usually run this size, but smaller crossovers and stock suspension setups often lack the clearance — check the driver’s door jamb sticker and owner’s manual for approved sizes, and confirm your wheel width sits inside the range printed on the tire’s spec sheet. A wider tire generally adds off-road footprint and curb presence while slightly increasing noise and rolling resistance — a trade most truck owners accept willingly. For a side-by-side look at tested options, our roundup of the best 305/55R20 tires covers the top all-terrain and highway picks.