Estimate revolutions per mile from a supported metric or flotation tire size or diameter, compare nominal tire geometry, solve a target diameter, or use a measured roll-out. Optional circumference reduction is a user-entered what-if assumption.

Enter a tire size or overall diameter. Blank optional values omit their outputs.

Nominal tire geometry is an estimate. Use measured rolling circumference or manufacturer data for calibration; static tire deflection does not establish rolling circumference.

For example 275/70R18 or 33×12.50R15.

Optional settings

Blank = 0%. Optional what-if model only, not static deflection or a measured loaded-tire correction.

Blank omits speed and RPM outputs.

Rev Per Mile Formula

The calculator finds tire revolutions per mile by dividing the number of inches in one mile by the tire circumference. If you enter a tire size, it first converts the tire size into an overall diameter.

Overall diameter mode

Rev / mi = 63360 / (pi × D)

Tire size mode

Sidewall = (W × (A / 100)) / 25.4
D = R + 2 × Sidewall
Rev / mi = 63360 / (pi × D)

Revolutions per kilometer

Rev / km = Rev / mi / 1.609344
  • Rev/mi = tire revolutions per mile
  • Rev/km = tire revolutions per kilometer
  • D = overall tire diameter in inches
  • W = tire section width in millimeters
  • A = aspect ratio as a percent
  • R = rim diameter in inches
  • Sidewall = sidewall height in inches
  • 63360 = inches in one mile
  • pi = approximately 3.14159

The tire size function uses the width, aspect ratio, and rim diameter from the tire sidewall. It calculates sidewall height, doubles it, adds the rim diameter, and then uses that diameter to find revolutions per mile.

The overall diameter function skips the tire-size conversion. It uses the diameter you enter directly after converting millimeters or centimeters to inches if needed.

The calculator distinguishes nominal geometric circumference from measured travel per revolution. Its optional percentage reduction is a user-assumed circumference model, not a prediction from static tire deflection.

Illustrative Geometric Revolutions Per Mile Ranges

These are geometric equivalents from an unloaded diameter, with rounded boundaries. They are not vehicle-category standards or measured rolling specifications.

Rev/mi range Unloaded geometric diameter General meaning
900+ Below about 22.41 in Small diameter, more turns per mile
750 to 900 About 22.41 to 26.89 in Calculated from circumference =pi×diameter
600 to 750 About 26.89 to 33.61 in Larger diameter, fewer turns per mile
Below 600 Above about 33.61 in Very large diameter, low revolutions per mile

Example Calculations

Example 1: Using tire size

You have a tire marked 275/70R16.

Sidewall = (275 × (70 / 100)) / 25.4 ≈ 7.579 in
D = 16 + 2 × (275 × 0.70 / 25.4) ≈ 31.157 in
Rev / mi = 63360 / (pi × 31.157) = 647.3

The tire makes about 647.3 revolutions per mile.

Example 2: Using overall diameter

You enter an overall tire diameter of 31.5 inches.

Rev / mi = 63360 / (pi × 31.5) = 640.3

The tire makes about 640.3 revolutions per mile.

FAQ

What does revolutions per mile mean?

Revolutions per mile means how many full turns a tire makes while traveling one mile. A smaller tire has a shorter circumference, so it turns more times per mile. A larger tire has a longer circumference, so it turns fewer times per mile.

Why is my calculated value different from a tire manufacturer spec?

The geometric formula uses nominal unloaded diameter. Real rolling circumference depends on tire construction and operating conditions. Static loaded radius is a different measurement and cannot establish rolling circumference through a universal 3% correction. Use measured or manufacturer rolling data for calibration.

Does changing tire size affect speedometer reading?

Yes. For a system calibrated to the original tire, actual speed =indicated speed×new diameter/original diameter in the nominal geometric model. Indication error as a percentage of actual speed =100×(original diameter/new diameter−1). Negative reads low; positive reads high. Actual rolling ratios may differ.