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275/65R18 in Inches: Tire Diameter, Width and Sidewall
A 275/65R18 tire is 32.1 inches (815 mm) tall and 10.8 inches (275 mm) wide, with a 7.0-inch sidewall, for a 18-inch rim. It turns 629 times per mile.
Example: 275/65R18. Also accepts 275/55-20 or 275 55 20.
| Measure | Inches | Millimetres |
|---|---|---|
| Overall diameter | 32.1 in | 815 mm |
| Section width | 10.8 in | 275 mm |
| Sidewall height | 7.0 in | 179 mm |
| Circumference | 100.8 in | 2559 mm |
| Rim diameter | 18 in | 457 mm |
| Revolutions per mile | 629 | |
| Revolutions per km | 391 |
Nominal size from the size code; real tires vary by brand, rim width and inflation. Fit on your vehicle is not checked.
275/65R18 tire size explained
The code 275/65R18 describes the tire in three numbers. The 275 is the section width in millimetres, which is 10.8 inches. The 65 is the aspect ratio, so the sidewall is 65% of 275 mm, or 179 mm (7.0 in). The 18 is the wheel diameter in inches (457 mm).
Add the rim and two sidewalls together and the tire stands 32.1 inches high. One full turn of the wheel carries the vehicle 100.8 inches (2.56 m), which is why a 275/65R18 makes about 629 turns in a mile. Speedometers, odometers and traction systems are set up for a particular size, so changing to a tire with a different diameter changes what they read.
New to size codes? See how to read a tire size, or use the tire size comparison calculator to put 275/65R18 next to the size you have now.
Sizes close to 275/65R18
These common sizes are within 3% of the 32.1-inch diameter of the 275/65R18. A small difference keeps the speedometer near right, but width, load rating and fit can still differ, so check each one.
| Size | Diameter | vs 275/65R18 | Width | Tool |
|---|---|---|---|---|
| 255/75R17 | 32.1 in | 0% | 10.0 in (255 mm) | Compare |
| 255/70R18 | 32.1 in | -0.1% | 10.0 in (255 mm) | Compare |
| 285/45R22 | 32.1 in | +0.1% | 11.2 in (285 mm) | Compare |
| 275/55R20 | 31.9 in | -0.5% | 10.8 in (275 mm) | Compare |
| 285/55R20 | 32.3 in | +0.8% | 11.2 in (285 mm) | Compare |
| 265/75R16 | 31.6 in | -1.3% | 10.4 in (265 mm) | Compare |
| 265/70R17 | 31.6 in | -1.5% | 10.4 in (265 mm) | Compare |
| 285/65R18 | 32.6 in | +1.6% | 11.2 in (285 mm) | Compare |
Changing to or from 275/65R18
If you move from 255/75R17 to 275/65R18, the overall diameter changes by 0% and the speedometer reads accordingly. The speedometer correction is the new diameter divided by the old one, so with a diameter 32.1 in the actual speed is the displayed speed multiplied by 32.1 and divided by the old diameter. The odometer follows the same ratio.
- Check the door-jamb placard for the size your vehicle was built for.
- Confirm the load index and speed rating are at least what the placard asks for.
- Ask whether your wheel width suits a 275 mm tire.
- Check clearance at full steering lock and over bumps; this is a common place where a larger tire rubs.
275/65R18 FAQ
How many inches is a 275/65R18 tire?
A 275/65R18 tire is about 32.1 inches (815 mm) tall overall, 10.8 inches (275 mm) wide, and has a sidewall of 7.0 inches (179 mm).
What does 275/65R18 mean?
275 is the section width in millimetres, 65 means the sidewall is 65% of the width, R means radial construction and 18 is the rim diameter in inches.
How many revolutions per mile does a 275/65R18 make?
About 629 revolutions per mile (391 per kilometre), based on a circumference of 100.8 inches.
Will a 275/65R18 tire fit my vehicle?
The size code alone cannot tell. Fit depends on your wheel width and offset, suspension and fender clearance. Check your door-jamb placard for the approved sizes and ask a tire shop.