Tire essentials
How tire size numbers work
A tire size mixes millimetres, a percentage and inches. Reading those units correctly is the first step to comparing two sizes.
Read 205/55 R16 in three parts
205 is the nominal section width in millimetres. 55 is the sidewall height as a percentage of that width. R denotes radial construction, and 16 is the nominal wheel bead-seat diameter in inches. The 55 is not a height in millimetres and the 16 is not the tire’s outside diameter.
Work out the dimensions
Multiply 205 by 0.55 to get a 112.75 mm sidewall. Convert the wheel: 16 × 25.4 = 406.4 mm. Add two sidewalls: 406.4 + 2 × 112.75 = 631.9 mm overall. This geometric estimate is useful for comparing sizes, but a manufacturer’s measured dimensions are preferable when clearances are tight.
Read beyond the size code
The full sidewall marking also includes a load index and speed symbol. Those are separate requirements; matching the width, ratio and rim does not establish load capacity or speed suitability. Construction and intended application matter too. Photograph the complete marking and check the vehicle placard before shopping.
Method and references
Examples use nominal geometry and fixed-price scenarios, with no vehicle-specific specifications implied. See our calculation methodology and editorial policy.
Dimension reference: Tire Rack: calculating tire dimensions. Consult the tire and vehicle manufacturers for actual fitment requirements.