How Big Is a 275/65R18 Tire? | Key Dimensions Explained

A 275/65R18 tire measures roughly 32 inches in diameter and about 11 inches wide, made to fit an 18-inch wheel.

For the full breakdown, see our best 275/65R18 Off Road Tires guide.

Whether you’re shopping for new tires or checking fitment, the numbers in 275/65R18 tell you exactly what will touch the road. The “275” is the section width in millimeters, “65” is the aspect ratio as a percentage of width, and “18” is the wheel diameter in inches. Combined, they give a tire that stands about 32 inches tall — a common size for light trucks and SUVs that need a balance of ride comfort and off-road capability.

Here’s a quick breakdown of what each part of the size code means and how it translates to real-world measurements.

275/65R18 Tire Dimensions: Metric and Standard

The standard conversion for 275/65R18 works out to an overall diameter of roughly 32.1 inches and a section width of about 10.8 inches. The sidewall height comes to about 7.0 inches, giving the tire a circumference of roughly 100.8 inches — which works out to approximately 629 revolutions per mile.

In metric terms, tire calculators like the one at 1010Tires show the same size as 275 millimeters wide with a sidewall height of 179 millimeters. Overall diameter lands at about 815 millimeters, with a rolling circumference of roughly 2559 millimeters.

One measurement people often mix up is section width versus tread width. The 275-millimeter figure is the widest point of the tire, measured from sidewall to sidewall — the actual tread that contacts the road is typically narrower than that.

What Size Rim Fits a 275/65R18 Tire?

Manufacturers generally recommend a rim width of 7.5 to 9.5 inches for passenger tires in this size, while LT variants often list a slightly narrower range of 7.5 to 9 inches. The right choice depends partly on the specific tire model, so checking the sidewall for the manufacturer’s approved rim width range is the reliable way to confirm fitment.

These numbers aren’t guesses — they’re published on tire spec sheets. For example, Pirelli’s catalog for the 275/65R18 Scorpion ATR lists rim width ranges and other technical data directly on their product page, alongside the load index and speed rating.

Load Index and Speed Rating for 275/65R18 Tires

Load index and speed rating are NOT fixed by tire size. A 275/65R18 tire can carry different ratings depending on the specific model. For instance, one tire in this size is rated 116T, while another is 116H. The number 116 refers to the load index — how much weight the tire can support at maximum inflation. In this case, 116 equals roughly 2,756 pounds per tire, according to some product specifications.

The letter indicates the speed rating. “H” means the tire is certified for up to 130 mph, while “T” caps at 118 mph. Here’s the catch: these ratings are model-specific, not size-specific. The Toyo Open Country A/T III and the Nokian Tyres One HT both come in 275/65R18, but they don’t necessarily share the same load and speed credentials. Always check the sidewall markings on the specific tire you’re considering.

If you’re looking for solid all-terrain options in this size, our tested roundup of the best 275/65R18 off-road tires breaks down which models handle dirt and gravel without sacrificing highway comfort.

Common Mistakes When Reading This Tire Size

The biggest error people make is treating 275/65R18 as a fixed product spec instead of a size category. Actual values like tread depth, maximum pressure, and load range depend entirely on the specific tire model. A 275/65R18 from one brand could have a different load range than one from another.

Another frequent mix-up is assuming the section width equals the tread width. The stamped 275 millimeters is the widest part of the tire, not the rubber that meets the pavement. Tread width is always narrower and varies by design.

Before buying, check the vehicle’s placard on the driver’s door jamb and verify the tire’s own load index, speed rating, and rim-width range.