Quick Answer
- Contact patch area = load on one tire / inflation pressure. 875 lb at 32 psi is 27.3 sq in (176 cm2), a little more than a 4 x 6 inch postcard.
- Michelin describes each of a car's four contact patches as roughly the size of a hand. Boeing publishes the same load / pressure calculation for aircraft tires.
- It is an approximation, and your vehicle's tire placard gives the pressure to use, measured when the tires are cold.
Contact patch area = load on one tire / inflation pressure. Use the load on a single tire and the cold pressure.
Contact patch area
27.3 sq in
In square centimetres
176 cm²
| For scale | Area | Contact patch is |
|---|---|---|
| Playing card (poker size, 2.5 x 3.5 in) | 8.8 sq in | 3.1 x |
| US dollar bill (6.14 x 2.61 in) | 16.0 sq in | 1.7 x |
| Postcard (4 x 6 in) | 24.0 sq in | 1.1 x |
| US letter sheet (8.5 x 11 in) | 93.5 sq in | 0.3 x |
875 lb / 32.0 psi = 27.34sq in. This is the pressure-area approximation, the same calculation Boeing publishes for aircraft tires. A real patch also depends on the tire construction and tread, and Michelin describes each of a car's four contact patches as roughly the size of a hand.
Get a plain-English explanation of your results and what they mean for your vehicle.
Contact Patch Area Chart: Load and Pressure
Contact patch area in square inches for the load on one tire (rows, lb) and the inflation pressure (columns, psi). The kPa equivalent of each pressure is in the header.
| Load on one tire | 28 psi193 kPa | 30 psi207 kPa | 32 psi221 kPa | 34 psi234 kPa | 36 psi248 kPa | 38 psi262 kPa | 40 psi276 kPa | 44 psi303 kPa |
|---|---|---|---|---|---|---|---|---|
| 600 lb (272 kg) | 21.4 | 20.0 | 18.8 | 17.6 | 16.7 | 15.8 | 15.0 | 13.6 |
| 700 lb (318 kg) | 25.0 | 23.3 | 21.9 | 20.6 | 19.4 | 18.4 | 17.5 | 15.9 |
| 800 lb (363 kg) | 28.6 | 26.7 | 25.0 | 23.5 | 22.2 | 21.1 | 20.0 | 18.2 |
| 900 lb (408 kg) | 32.1 | 30.0 | 28.1 | 26.5 | 25.0 | 23.7 | 22.5 | 20.5 |
| 1000 lb (454 kg) | 35.7 | 33.3 | 31.3 | 29.4 | 27.8 | 26.3 | 25.0 | 22.7 |
| 1100 lb (499 kg) | 39.3 | 36.7 | 34.4 | 32.4 | 30.6 | 28.9 | 27.5 | 25.0 |
| 1200 lb (544 kg) | 42.9 | 40.0 | 37.5 | 35.3 | 33.3 | 31.6 | 30.0 | 27.3 |
| 1500 lb (680 kg) | 53.6 | 50.0 | 46.9 | 44.1 | 41.7 | 39.5 | 37.5 | 34.1 |
Pressure conversions are on the PSI to kPa converter, and a tire pressure and volume view is on the tire air volume calculator.
How Big Is a Tire Contact Patch? Size Compared
The 875 lb at 32 psi example (27.3 sq in) against everyday objects, and what the sources say.
| Object | Area | Contact patch is |
|---|---|---|
| Playing card (poker size, 2.5 x 3.5 in) | 8.8 sq in | 3.1 x |
| US dollar bill (6.14 x 2.61 in) | 16.0 sq in | 1.7 x |
| Postcard (4 x 6 in) | 24.0 sq in | 1.1 x |
| US letter sheet (8.5 x 11 in) | 93.5 sq in | 0.3 x |
| Source | Statement (paraphrased) |
|---|---|
| Michelin USA | Every braking event, turn and acceleration goes through four contact patches roughly the size of a hand (Importance of Tire Maintenance). |
| Michelin Canada | Four contact patches, each roughly the size of your hand, are all that separate you from the road (Why do tires matter). |
| Michelin USA | Overinflated tires reduce the contact patch, which affects traction and makes the vehicle more sensitive to road irregularities. Underinflation wears the outer edges and overinflation the center, and underinflated tires run hotter and have higher rolling resistance. |
| Boeing | The tire contact area for an aircraft tire is calculated by dividing the single wheel load by the tire inflation pressure, with load in pounds and pressure in psi giving square inches. The footprint is usually understood as an ellipse whose long axis is 1.6 times the short axis. |
| NHTSA | Check tire pressure when the tires are cold, meaning the vehicle has not been driven for at least three hours, and use the pressure on the placard or in the owner's manual. |
Tire Contact Patch Formula
Area from load and pressure
Area (sq in) = load on one tire (lb) / pressure (psi). For 875 lb at 32 psi: 27.34 sq in. In cm2, multiply by 6.4516: 176 cm2.
Metric units
Area (cm2) = load (kg) x 9.80665 N / pressure (kPa) x 10, or convert to lb and psi first. 875 lb is 397 kg and 32 psi is 221 kPa.
Load on one tire
Use the corner weight of the vehicle. Dividing the total weight by four is an average, and the front and rear axles usually carry different loads.
Why it is only an estimate
The formula assumes the air pressure supports the load over the whole patch. A real patch is shaped by the tire construction, sidewall stiffness and tread, so measure it with a paper or ink print for an accurate figure.
How to Use the Contact Patch Calculator
- 1Enter the load on one tire (the corner weight) in pounds or kilograms.
- 2Enter the tire pressure in psi or kPa. Use the cold pressure from your tire placard.
- 3Read the contact patch area in square inches and square centimetres, and compare it with the playing card, dollar bill, postcard and letter sheet.
- 4Check the load and pressure chart for other combinations.