265/65R18 measures 31.6″ overall diameter and 10.4″ section width. Sidewall height is 6.8″, circumference is 99.2″, and the tire turns 639 times per mile. Those figures are geometry off the stamped size, not a brand or load range.
265/65R18 dimensions
| Measurement | Inches | Metric |
|---|---|---|
| Overall diameter | 31.6″ | 802 mm |
| Section width | 10.4″ | 265 mm |
| Sidewall height | 6.8″ | 172 mm |
| Circumference | 99.2″ | 2519 mm |
| Revolutions per mile | 639 | 397 / km |
The stamped width is 265 mm (10.4″). The aspect ratio is 65, so the sidewall is 65% of that width, which is 6.8″. The rim is 18 inches. Overall diameter is the rim plus two sidewalls: 18 + 2 × 6.8″ = 31.6″.
Sizes near 265/65R18
A swap that stays inside about 3% diameter usually keeps the speedometer honest and clears the same well. 255/70R18 is a close neighbour at +1.6% diameter. The percent column opens both stamps in the comparison calculator.
| Size | Diameter | Width | vs 265/65R18 |
|---|---|---|---|
| 255/70R18 | 32.1″ | 10.0″ | +1.6% |
| 285/65R17 | 31.6″ | 11.2″ | +0.1% |
| 275/65R18 | 32.1″ | 10.8″ | +1.6% |
| 265/70R17 | 31.6″ | 10.4″ | +0.1% |
| 265/75R16 | 31.6″ | 10.4″ | +0.3% |
| 285/70R16 | 31.7″ | 11.2″ | +0.5% |
How to read the stamped size
265/65R18 is a metric size: width in millimetres, aspect ratio as a percent of that width, then the rim diameter in inches after the R. The how to read tire size page walks the whole sidewall, including load index and speed rating, which this page does not use.
Diameter and width tell you whether a size is in the same family as what you have. They do not tell you whether 265/65R18 clears your fenders, matches your wheel width, or is load-rated for the vehicle. Check the door-jamb sticker and the wheel well before you buy.
Speedometer and revs
At 639 revolutions per mile, a trip computer calibrated for 265/65R18 is reading true only while this diameter is on the truck. A taller replacement under-reads speed and distance by the same percent the diameter grew. A shorter one over-reads. The comparison calculator puts a second size next to 265/65R18 and shows the error at 60 mph.