Calculate ground pressure from load and contact area, or find required footprint area or supported load in kPa, psi, Pa, or bar as needed.
Ground Pressure Formula
Ground pressure is the force a load applies to the surface it sits on, divided by the contact area. The calculator uses one base formula and rearranges it depending on which tab you are using.
P = F / A
When you enter mass instead of force, the calculator first converts mass to force using gravity:
F = m * g
For the footprint mode, the total contact area is built from the dimensions of each track, tire, mat, or pad:
A = L * W * n
- P = ground pressure (Pa, kPa, psi, or bar)
- F = vertical force on the ground (N or kN)
- A = total contact area (m², ft², in², cm²)
- m = mass of the load (kg, tonnes, lb, US tons)
- g = 9.80665 m/s², acceleration due to gravity
- L = contact length of one track, tire, or pad
- W = contact width of one track, tire, or pad
- n = number of contact areas sharing the load
The Pressure tab uses P = F / A directly when you already know the total contact area. The Footprint tab calculates A from length, width, and count first, then divides force by that area. The Solve tab rearranges the same formula to find area (A = F / P) or load (F = P * A) when you know the other two values.
Typical Ground Pressure Values
Use these tables to sanity-check a result or to pick a target pressure for soft ground.
| Source of load | Approx. pressure (kPa) | Approx. pressure (psi) |
|---|---|---|
| Adult standing, both feet | 14 to 20 | 2 to 3 |
| Adult walking, one foot | 28 to 60 | 4 to 9 |
| Tracked excavator, low ground pressure | 25 to 45 | 3.6 to 6.5 |
| Standard tracked excavator | 45 to 80 | 6.5 to 12 |
| Passenger car tire | 200 to 240 | 29 to 35 |
| Loaded truck tire | 600 to 900 | 85 to 130 |
| Main battle tank | 95 to 110 | 14 to 16 |
| Soil type | Safe bearing pressure (kPa) | Safe bearing pressure (psi) |
|---|---|---|
| Soft clay or peat | 25 to 50 | 3.6 to 7 |
| Firm clay | 75 to 150 | 11 to 22 |
| Loose sand or gravel | 100 to 200 | 14 to 29 |
| Compact sand or gravel | 200 to 600 | 29 to 87 |
| Soft rock | 600 to 2000 | 87 to 290 |
Worked Examples
Example 1: Tracked excavator. A 20 tonne excavator sits on two tracks, each 3.355 m long and 0.6 m wide. Total contact area is 2 * 3.355 * 0.6 = 4.026 m². Force is 20,000 * 9.80665 = 196,133 N. Pressure is 196,133 / 4.026 = about 48,710 Pa, or 48.7 kPa (7.06 psi). That falls in the standard tracked excavator range.
Example 2: Required crane mat size. A crane outrigger pushes down with 250 kN onto soft clay rated at 50 kPa. Required mat area is 250,000 / 50,000 = 5 m². A square mat would need to be at least about 2.24 m on a side to spread the load to a safe pressure.
FAQ
Is ground pressure the same as weight? No. Weight is a force. Ground pressure is that force spread over the contact area. Two machines with the same weight can produce very different ground pressures depending on their tracks or tires.
Why use mass times gravity? The ground reacts to force, not mass. A kilogram of mass produces about 9.81 newtons of force at the Earth's surface, so the calculator multiplies mass by 9.80665 m/s² before dividing by area.
Should I count all tires or tracks? Yes, if the load is shared evenly. Enter the count in the Footprint tab and the calculator multiplies one footprint by that number to get total contact area. If the load is not shared evenly, calculate each contact patch separately.
How does ground pressure compare to soil bearing capacity? The ground pressure your equipment produces should stay below the safe bearing pressure of the soil under it. If it does not, you need wider tracks, more tires, crane mats, or timber to spread the load.
