Tyre Size Calculator
Calculate tyre sidewall height and overall wheel diameter.
Sidewall height
112.8mm
- Overall diameter
- 631.9 mm
- Circumference
- 1,985.2 mm
v1.0 · Reviewed September 2026
How this is worked out
Sidewall height is the tyre width × the aspect profile. Overall diameter is the rim diameter converted to millimetres at 25.4 mm an inch, plus two sidewalls. Circumference is diameter × π.
Worked example
- 205 mm wide
- 55 profile
- 16 inch rim
205 × 55% = 112.8 mm sidewall, and 16 × 25.4 + 2 × 112.8
112.8 mm sidewall, 631.9 mm overall diameter
Assumptions and limits
- Nominal dimensions from the size code. Real fitted tyres vary a little between manufacturers and change slightly with pressure, load and wear.
- Changing to a size with a different overall diameter alters your speedometer and odometer readings, and may affect insurance and MOT compliance.
- Does not check load index, speed rating or whether the size physically fits the vehicle.