Tire Size Calculator calculates tire diameter, circumference, revolutions per mile/km from the tire size designation on a tire.

This calculator also gives the option to compare tires. e.g., It compares the circumference and the outer diameter of one or more additional tires to the base tire and gives an information about upsizing/downsizing: does the new tire exceeds the recommended upper or lower limit for upsizing/downsizing. Also it shows the amount of speedo error due to changing the tire diameter/circumference.

 

At the bottom of the page there are detailed instructions how to use this calculator and about the tire size designation.

Tire Size Calculator

Tire Size Calculator

select tire size

eg. 195/65R15

 / R

Tire Dimensions

Tire Size-
mminches
Tire
Width
--
Aspect
Ratio
--
Rim
Diameter
--
Sidewall
Height
--
Tire
Diameter
--
Circum-
ference
--
Revolutions--

Click on this button to compare this tire dimensions to the base tire, which is the first calculated tire size in the "Tire Size Calculator" and the basis for the comparision.

To make this button work, get dimensions for at least one more tire, besides the first entered in the calculator.

After you click on the "Compare this tire" button, the last calculated tire size dimensions will be added for the comparision in the "Comparing Tires" form below.

Comparing Tires

Measurement units

Base tire
Tire Size-
mmdiff
Tire
Width
--
Aspect
Ratio
--
Rim
Diameter
--
Sidewall
Height
--
Tire
Diameter
--
Circum-
ference
--
Revolutions--
-

To compare another two tires to the first selected tire (the base tire for comparision) click on the button "Clear Compared Tires".

To start over, with the new tire size for the base tire - please refresh the page.

A negligible error can arise due to rounding off numbers.

Disclaimer:
The calculator results are for informative purposes only. The tyresizecalculator.com is not responsible for any miscalculations of this calculator or any errors that may arise with its usage.

Try out our other calculators:

  • Find out which tire dimensions are adequate for your new wheels with Plus Sizing Calculator.
  • Check the speedometer for the speedo error which may arise from the tyre size change, for any speedometer reading.
  • Find out which wheel size is suitable for your new tyres.
  • Find the wheel offset and the wheel backspace, the important measurements for positioning the wheel/tyre assembly inside the wheel well.
  • The tire size converter will convert the inch tire size to the metric tire size and the other way around. The converter also displays adequate real tires with the dimensions which are closest to the calculated tire size, if such exist.

Related articles:

The Tire Size Designation

The tire size designation is consisted of the following elements:

[Tire Width]/[Aspect Ratio]R[Rim Diameter]

For example tire size 195/65R15 has:

Tire Width = 195 mm

Aspect Ratio = 65%

Aspect Ratio is the sidewall height as a percentage of the section width. For example, sidewall height of this tire will be 195 x 0.65 = 126.75 mm

Tire type = R - Radial-ply structure

Rim Diameter = 15 inches

How to use the Tire Size Calculator and how to compare the tire dimensions

To get the tire dimensions for a tire, first select the tire size, then click on the "Calculate Tire Dimensions" button. The dimensions for the selected tire size will be presented in the table below the calculator.

Compare tire dimensions

The first selected/entered tire size in the Tire Size Calculator is the base tire for a comparision to the other tires.

You have an option to compare two additional tire sizes to the base tire. To use this option, after you've got dimensions for the first selected tire size - the base tire, select the another tire size and click again on the "Calculate Tire Dimensions" button to get the dimensions for that tire size.

After that, the "Compare this tire" button will be enabled and you can click on it to add the last calculated tire size dimensions for a comparision. The results of the comparision are presented in the form: "Comparing Tires", at the bottom of this page.

Every compared tire, with its dimensions, is contained in a section called "Compared Tire x" and it has the column "Diff" which shows the calculated differences for its dimensions compared to the base tire.

At the bottom of this page there is the "Clear compared tires" button which, when clicked, clears all the tires selected for the comparision, and you can start again, to add the new tire sizes you want to compare to the base tire.

If you want to change the base tire, which is a basis for the comparision with the other selected tires, simply refresh this page.