Tire Diameter Calculator
Calculate tire diameter from a metric size code. See the formula and compare the result in millimeters, inches and centimeters.
Estimate nominal overall diameter.
Tire Diameter Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Tire Diameter Calculator Works?
The Tire Diameter Calculator works by adding two sidewall heights to the rim diameter. The calculation takes 3 steps.
Read the size code
Find the size on the sidewall, for example 265/70 R17, and enter the 3 numbers.
Calculate sidewall height
The calculator multiplies the 265 mm width by 70% to get a 185.5 mm (7.30 in) sidewall.
Add the rim
The calculator converts the 17-inch rim to 431.8 mm and adds 2 sidewalls for an overall diameter of 802.8 mm (31.61 in).
Tire Diameter Calculator Formula
The Tire Diameter Calculator formula is OD = (2 × W × AR ÷ 100) + (Rim × 25.4), with the result in millimeters.
OD = 2 × W × AR ÷ 100 + Rim × 25.4OD_in = OD ÷ 25.4OD_cm = OD ÷ 10- W
- Section width (mm)
- AR
- Aspect ratio (%)
- Rim
- Rim diameter (in)
- 25.4
- Millimeters per inch
Worked example
A 205/55 R16 tire has a sidewall of 205 × 0.55 = 112.75 mm. The rim adds 16 × 25.4 = 406.4 mm. The overall diameter is 2 × 112.75 + 406.4 = 631.9 mm (24.88 in, 63.2 cm).
Tire Diameter Calculator Conversion Table
The Tire Diameter Calculator conversion table lists the nominal overall diameter of 10 common passenger and light truck sizes in 3 units.
| Size | Sidewall height | Diameter (mm) | Diameter (in) | Diameter (cm) |
|---|---|---|---|---|
| 195/65 R15 | 126.8 mm | 634.5 mm | 24.98 in | 63.5 cm |
| 205/55 R16 | 112.8 mm | 631.9 mm | 24.88 in | 63.2 cm |
| 215/60 R16 | 129.0 mm | 664.4 mm | 26.16 in | 66.4 cm |
| 225/45 R17 | 101.2 mm | 634.3 mm | 24.97 in | 63.4 cm |
| 225/65 R17 | 146.2 mm | 724.3 mm | 28.52 in | 72.4 cm |
| 235/45 R18 | 105.8 mm | 668.7 mm | 26.33 in | 66.9 cm |
| 245/40 R18 | 98.0 mm | 653.2 mm | 25.72 in | 65.3 cm |
| 255/35 R19 | 89.2 mm | 661.1 mm | 26.03 in | 66.1 cm |
| 265/70 R17 | 185.5 mm | 802.8 mm | 31.61 in | 80.3 cm |
| 275/55 R20 | 151.2 mm | 810.5 mm | 31.91 in | 81.0 cm |
What is Tire Diameter Calculator?
A Tire Diameter Calculator is a tool that converts a tire size code into the overall height of the tire from ground to top of tread. Overall diameter (OD) is the single number that controls speedometer accuracy, gearing and ground clearance.
The result is the nominal diameter of a new, unloaded tire. A tire on a vehicle sits 3% to 6% lower at the bottom (the loaded radius), and tread wear removes up to 16 mm (0.63 in) of diameter over the tire's life.
Metric sizes need the calculator. Flotation sizes such as 33x12.50R17 already state the diameter (33 in) in the code.
What are the uses of Tire Diameter Calculator?
There are 5 main uses of the Tire Diameter Calculator, including fender clearance checks and gearing math.
Fender clearance checks
Compare the tire height with the measured gap inside the wheel arch.
Metric-to-inch sizing
Express a metric tire as an inch height, for example 265/70 R17 as a 31.6-inch tire.
Gearing calculations
Feed the diameter into axle ratio and engine RPM calculations.
Spare tire matching
Confirm a spare tire's height against the road tires.
Lift kit planning
Pick a tire height that matches the lift height of a truck or SUV.
Related Core Tire Dimensions Tools
View All 134 Subtools →Compare two tire sizes.
Compare several sizes together.
Calculate absolute and percentage differences.
Estimate nominal circumference.
Compare estimated rolling distances.
Compare nominal section widths.