Decoders & Converters

Tire Dimension Unit Converter

Convert tire dimensions between millimeters, centimeters, inches and feet. Includes rim sizes, widths, diameters and 32nds of an inch.

Decoders & Converters

Convert millimeters, inches, and centimeters.

Open Live Calculator

Tire Dimension Unit Converter: Tire Size Inputs

Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.

ISO/TRA Compliant

Baseline Tire (T1)Stock OEM

Width (mm)

Aspect (%)

Rim (in)

Comparison Tire (T2)Proposed Setup

Width (mm)

Aspect (%)

Rim (in)

Baseline OD634.3 mm24.97"

Comparison OD637.2 mm25.09"

Diameter Variance+2.9 mm+0.46%

Speed @ 60 MPH60.3 MPH-4 revs/mi

How Tire Dimension Unit Converter Works?

The Tire Dimension Unit Converter works by applying the exact factor of 25.4 millimeters per inch to any tire dimension entered. The tool uses 3 steps.

Pick the input unit
Choose millimeters, centimeters, inches or feet.
Enter the value
Type a width, sidewall, diameter or rim value, for example 245 mm.
Read all units
The converter returns 24.5 cm, 9.646 in, 0.804 ft and 308.7/32 in at once.

Tire Dimension Unit Converter Formula

The Tire Dimension Unit Converter formula is inches = millimeters ÷ 25.4, and millimeters = inches × 25.4.

mm → inin = mm ÷ 25.4

in → mmmm = in × 25.4

mm → cmcm = mm ÷ 10

in → ftft = in ÷ 12

in → 32ndsn/32 = in × 32

25.4: Exact millimeters per inch (international inch, 1959)
32: Thirty-seconds per inch, the US tread depth unit

Worked example

A 17-inch rim equals 17 × 25.4 = 431.8 mm (43.18 cm). A 285 mm section width equals 285 ÷ 25.4 = 11.22 in.

Tire Dimension Unit Converter Conversion Table

The Tire Dimension Unit Converter conversion table converts 12 common tire measurements into 5 units, from 100 mm widths to a 33-inch (838.2 mm) diameter.

Common tire dimensions in 5 units
Millimeters	Centimeters	Inches	Feet	32nds of an inch
100 mm	10 cm	3.937 in	0.328 ft	126.0/32 in
125 mm	12.5 cm	4.921 in	0.410 ft	157.5/32 in
150 mm	15 cm	5.906 in	0.492 ft	189.0/32 in
200 mm	20 cm	7.874 in	0.656 ft	252.0/32 in
225 mm	22.5 cm	8.858 in	0.738 ft	283.5/32 in
250 mm	25 cm	9.843 in	0.820 ft	315.0/32 in
300 mm	30 cm	11.811 in	0.984 ft	378.0/32 in
431.8 mm	43.18 cm	17.000 in	1.417 ft	544.0/32 in
508 mm	50.8 cm	20.000 in	1.667 ft	640.0/32 in
635 mm	63.5 cm	25.000 in	2.083 ft	800.0/32 in
762 mm	76.2 cm	30.000 in	2.500 ft	960.0/32 in
838.2 mm	83.82 cm	33.000 in	2.750 ft	1056.0/32 in

What is Tire Dimension Unit Converter?

A Tire Dimension Unit Converter is a tool that converts tire widths, heights and rim sizes between metric and imperial units. Tire sizes mix millimeters and inches in one code, so unit conversion is part of nearly every tire calculation.

The inch has equaled exactly 25.4 mm since 1959. The converter uses that exact factor without rounding.

US tread depth uses 32nds of an inch, so the converter adds a 32nds column for tread and small measurements.

What are the uses of Tire Dimension Unit Converter?

There are 4 main uses of the Tire Dimension Unit Converter, including measurement checks and parts ordering.

Measurement checks
Convert a tape-measured gap in inches to the mm values of a size code.
Parts ordering
Convert wheel and spacer dimensions between supplier catalogs.
Spec sheet reading
Read metric data books in imperial units and the reverse.
Clearance notes
Record fender and strut gaps in both units.