OEM Tire Size Lookup
Find the size your car came with. Use the calculator below. Results update as you type.
How the OEM Tire Size Lookup Works
This lookup works by pointing you to the documented factory tire record for your vehicle and reading the size, pressure, load and speed values from it. OEM stands for original equipment manufacturer.
- Open the driver door and find the tire placard on the door jamb (B-pillar).
- Read the front and rear sizes, for example 235/55R19 101V.
- Read the cold pressures, for example 36 psi (250 kPa).
- Enter the size in the lookup to see diameter, revs per mile and approved alternatives.
The Formula
The formula has no calculation step; it reads the placard size and then applies the standard diameter formula.
OEM Size = Placard[Front], Placard[Rear] Overall Diameter = (Rim × 25.4) + 2 × (Width × Aspect Ratio ÷ 100)Worked example: a placard size of 225/65R17 102H gives a 28.52 in (724.3 mm) diameter, a 102 load index (850 kg, 1,874 lb) and an H speed rating (210 km/h, 130 mph).
Conversion Table
The conversion table lists 7 places where the factory tire size is recorded and what each one shows. The door placard and owner's manual list all 3 values: size, pressure and service description.
The tire currently on the car is the weakest source. A previous owner can have fitted a different size.
| Source | Location | Lists Size | Lists Pressure | Lists Load / Speed |
|---|---|---|---|---|
| Tire placard | Driver door jamb (B-pillar) | Yes | Yes | Yes |
| Owner's manual | Tires and wheels chapter | Yes | Yes | Yes |
| Fuel door label | Inside fuel flap (many EU cars) | Yes | Yes | Sometimes |
| Glovebox label | Inside glovebox lid | Sometimes | Yes | Sometimes |
| Window sticker | Monroney label (US) | Yes | No | No |
| Build sheet / VIN decode | Dealer or maker portal | Yes | No | Sometimes |
| Current tire sidewall | On the tire | Yes (may not be OEM) | Max only | Yes |
What Is the OEM Tire Size Lookup?
The OEM Tire Size Lookup is a tool that finds the tire size the vehicle maker fitted at the factory. The OEM size is the baseline for every comparison and fitment calculation.
The vehicle's speedometer, ABS, stability control and load ratings were all set for the OEM size. A replacement should match it or stay inside the ±3% diameter window.
Common Uses
This lookup has 4 uses: replacement baselines, used-car checks, pressure setting and staggered checks.
- Set a baseline: Use the OEM size for all comparisons.
- Check used cars: Confirm fitted tires match the placard.
- Set pressure: Use the placard's cold pressure.
- Check staggered setups: See if front and rear sizes differ.