Passenger Car Tire Size Calculator
Read a car tire code and see each size. Use the calculator below. Results update as you type.
How the Passenger Car Tire Size Calculator Works
This calculator works by decoding P-metric or Euro-metric passenger sizes and returning diameter, sidewall and revs per mile. It handles sizes with or without the P prefix.
- Enter the size, for example P215/55R17.
- Read the type: P-metric.
- Read the diameter: 26.31 in (668 mm).
- Read the sidewall (4.66 in) and revs per mile (767).
The Formula
The formula is the standard diameter formula, with the prefix used only to select the load standard.
Overall Diameter = (Rim × 25.4) + 2 × (Width × Aspect Ratio ÷ 100) Revs per Mile = 63,360 ÷ (π × Diameter (in))P-metric and Euro-metric tires of the same size have the same nominal dimensions. Their load tables differ slightly. Worked example: 245/40R19 has a 98 mm sidewall, a 678.6 mm (26.72 in) diameter and 755 revs per mile.
Conversion Table
The conversion table lists 12 passenger sizes, 6 P-metric and 6 Euro-metric. Diameters run from 24.21 in (P195/60R15) to 27.03 in (255/35R20).
Most passenger tires fall between 24 in and 28 in (610–711 mm). That narrow band keeps car speedometers close across many sizes.
| Size | Type | Diameter (in / mm) | Sidewall (in) | Revs / Mile |
|---|---|---|---|---|
| P185/65R15 | P-metric | 24.47 / 622 | 4.73 | 824 |
| P195/60R15 | P-metric | 24.21 / 615 | 4.61 | 833 |
| P205/55R16 | P-metric | 24.88 / 632 | 4.44 | 811 |
| P215/55R17 | P-metric | 26.31 / 668 | 4.66 | 767 |
| P225/50R17 | P-metric | 25.86 / 657 | 4.43 | 780 |
| P235/45R18 | P-metric | 26.33 / 669 | 4.16 | 766 |
| 195/65R15 | Euro-metric | 24.98 / 634 | 4.99 | 807 |
| 205/60R16 | Euro-metric | 25.69 / 652 | 4.84 | 785 |
| 215/45R17 | Euro-metric | 24.62 / 625 | 3.81 | 819 |
| 225/40R18 | Euro-metric | 25.09 / 637 | 3.54 | 804 |
| 245/40R19 | Euro-metric | 26.72 / 679 | 3.86 | 755 |
| 255/35R20 | Euro-metric | 27.03 / 686 | 3.51 | 746 |
What Is the Passenger Car Tire Size Calculator?
The Passenger Car Tire Size Calculator is a tool that processes passenger car tire markings into dimensions. Passenger sizes come in 2 standards: P-metric, from the Tire and Rim Association in the US, and Euro-metric, from ETRTO in Europe.
The 2 standards share dimensions but use slightly different load tables. Euro-metric sizes usually carry a slightly higher load index than the P-metric version of the same size.
Common Uses
This calculator has 4 uses: car replacements, P-to-Euro swaps, sedan upgrades and small-car checks.
- Replace car tires: Decode the placard size.
- Swap P-metric for Euro-metric: Check matching dimensions.
- Upgrade sedans: Compare Plus-1 options.
- Check small cars: Decode 14 in and 15 in sizes.