[TireFitLab](https://tirefitlab.com/) › [Tire & wheel reference guides](https://tirefitlab.com/learn/) › Tire section width guide # Tire section width guide ## What does the section width number mean? The section width (e.g. 205 in 205/55R16) is the widest measurement of the unmounted tire in millimetres, measured from sidewall to sidewall. A wider tire generally provides more grip but increases rolling resistance and may not fit narrower rims or tight wheel arches. ## Decode a tire size Type the main sidewall size string to see the width, profile and sidewall math. Tire size ### Section width 225 mm ### Aspect ratio 45% ### Sidewall height 101.3 mm ### Overall diameter 634.3 mm Reference-table value only. Always match your vehicle placard and tire sidewall markings. ## Worked examples Metric and flotation markings look different, but the table is calculated from the same nominal diameter, width and rim-size rules. | Size | Overall diameter | Section width | Sidewall | Circumference | | --- | --- | --- | --- | --- | | 225/45R17 | 24.97 in / 634 mm | 8.86 in / 225 mm | 3.99 in / 101.3 mm | 78.45 in / 1993 mm | | 285/75R16 | 32.83 in / 834 mm | 11.22 in / 285 mm | 8.42 in / 213.8 mm | 103.14 in / 2620 mm | | 33x12.50R15 | 33.00 in / 838 mm | 12.50 in / 318 mm | 9.00 in / 228.6 mm | 103.67 in / 2633 mm | **What to do with it:** Round marketing sizes can hide several millimetres of difference. - [165mm](https://tirefitlab.com/learn/section-width/165mm/) - [175mm](https://tirefitlab.com/learn/section-width/175mm/) - [185mm](https://tirefitlab.com/learn/section-width/185mm/) - [195mm](https://tirefitlab.com/learn/section-width/195mm/) - [205mm](https://tirefitlab.com/learn/section-width/205mm/) - [215mm](https://tirefitlab.com/learn/section-width/215mm/) - [225mm](https://tirefitlab.com/learn/section-width/225mm/) - [235mm](https://tirefitlab.com/learn/section-width/235mm/) - [245mm](https://tirefitlab.com/learn/section-width/245mm/) - [255mm](https://tirefitlab.com/learn/section-width/255mm/) - [265mm](https://tirefitlab.com/learn/section-width/265mm/) - [275mm](https://tirefitlab.com/learn/section-width/275mm/) - [285mm](https://tirefitlab.com/learn/section-width/285mm/) - [295mm](https://tirefitlab.com/learn/section-width/295mm/) - [305mm](https://tirefitlab.com/learn/section-width/305mm/) [Tire & wheel reference guides](https://tirefitlab.com/learn/) · [How to read a tire size](https://tirefitlab.com/learn/how-to-read-tire-size/) · [Rim diameter guide](https://tirefitlab.com/learn/rim/) Seasonal check ## Planning a long summer drive? Use the budget and running-cost tools before a trip, especially if the current tires are worn or the replacement size changes diameter. [Estimate tire budget](https://tirefitlab.com/tire-budget-calculator/) ## More in this topic: Size validation Decode markings, compare sizes, and understand diameter, load and speed changes. - [**How to read a tire size** How to read a tire size: decode every number and letter in P205/55R16 91V — width, aspect ratio, rim diameter, load index, speed rating.](https://tirefitlab.com/learn/how-to-read-tire-size/) - [**Tire type guide — P, LT, metric, radial & flotation** What do the letters in a tire size mean? P, LT, metric, radial (R) and flotation tire types explained.](https://tirefitlab.com/learn/tire-types/) - [**Tire sidewall markings decoder** Complete guide to every marking on a tire sidewall: size string, construction code, load index, speed rating, DOT date, M+S, 3PMSF snowflake, UTQG, max pressure, country of manufacture, and brand-specific symbols.](https://tirefitlab.com/learn/tyre-sidewall-markings/) - [**Tire load index chart** Use the tire load index chart to convert ratings 60–130 into kg and lb, then verify the vehicle placard and axle-load requirements.](https://tirefitlab.com/learn/load-index/) ### Useful tools [Tire size converter (mm ↔ inches)](https://tirefitlab.com/tire-size-converter/)[Tire size calculator](https://tirefitlab.com/tire-size-calculator/) ### Technical check 2026-06-28 ### Content updated 2026-06-21 What changed - Checked generated routes, metadata, sitemap inclusion and localized page rendering. [Methodology](https://tirefitlab.com/methodology/)