tyre diameter calculator

Tyre Diameter Calculator

Need to calculate tyre diameter quickly and accurately? Our free Tyre Diameter Calculator helps you work out the overall tyre diameter from the tyre width, profile and wheel rim size.

Whether you are checking:

• 205/55 R16 tyre diameter
• 225/40 R18 tyre diameter
• 255/35 R19 tyre diameter
• 285/30 R20 tyre diameter

This simple online tool makes tyre size calculations fast and easy.

How to Calculate Tyre Diameter

Tyre diameter is calculated using the tyre width, aspect ratio and rim size.

Formula:

((Tyre Width × Aspect Ratio ÷ 100) × 2 ÷ 25.4) + Rim Size = Overall Diameter in Inches

Tyre Diameter Example

If you want to calculate the diameter of a 225/40 R18 tyre:

Sidewall height = 225 × 40 ÷ 100 = 90mm

90mm × 2 = 180mm

180 ÷ 25.4 = 7.087 inches

7.087 + 18 = 25.087 inches

So, a 225/40 R18 tyre has an overall diameter of approximately 25.09 inches.

What Is Tyre Width?

Tyre width is the first number in a tyre size. For example, in 225/40 R18, the tyre width is 225mm.

What Is Tyre Profile?

Tyre profile, also known as aspect ratio, is the second number in a tyre size. It shows the sidewall height as a percentage of the tyre width. For example, in 225/40 R18, the profile is 40%.

What Is Rim Size?

Rim size is the wheel diameter in inches. For example, in 225/40 R18, the rim size is 18 inches.

Common Tyre Diameter Examples

• 205/55 R16 = approximately 24.88 inches
• 225/45 R17 = approximately 24.97 inches
• 225/40 R18 = approximately 25.09 inches
• 255/35 R19 = approximately 26.03 inches
• 275/30 R20 = approximately 26.50 inches

Why Use Our Tyre Diameter Calculator?

• Calculate overall tyre diameter instantly
• Useful for wheel and tyre upgrades
• Helps compare different tyre sizes
• Useful for cars, vans and performance vehicles
• Simple and easy to use