Look up the overall diameter, section width and rim size in inches for popular metric tire sizes (e.g. 225/45R17).
Automotive • metric ↔ inches
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The metric "P-metric" tire code (e.g. 225/45R17) was standardised in the late 1970s and is now used worldwide, but the older US flotation system describes tires directly in inches (e.g. 31×10.50R15). Drivers swapping wheels, fitting larger tires, or comparing options often need the overall diameter in inches — which also affects speedometer accuracy and gearing.
Overall diameter is calculated as: rim diameter + 2 × (section width × aspect ratio). For 225/45R17 that is 17 + 2 × (225 × 0.45 ÷ 25.4) ≈ 24.97 inches. This table lists popular sizes with their computed diameter, section width and rim so you can match a metric size to its real-world inch dimensions at a glance.