Calculate average ground pressure from load and effective contact area, or find area at a target pressure or an equivalent load. These arithmetic results do not establish allowable soil capacity or a safe support design.
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 the selected task.
When you enter mass instead of force, the calculator first converts mass to force using gravity:
For the footprint mode, the total contact area is built from the dimensions of each track, tire, mat, or pad:
- 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, metric tonnes, lb mass, US short tons)
- g = 9.80665 m/s², standard gravity used for mass-to-force conversion
- 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 tasks use P = F / A with a direct contact area or identical rectangular footprint dimensions and a whole count. The load tasks use F = P * A with either area method. The area task uses A = F / P with a positive target pressure. These are average static-pressure calculations.
Typical Ground Pressure Values
These retained ranges are illustrative, unverified examples for arithmetic comparison. They are not equipment specifications or site-specific allowable bearing pressures. Use actual equipment data and a site-specific ground assessment to determine applicable pressures.
| Source of load | Illustrative pressure (kPa) | Illustrative 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 | Illustrative soil pressure (kPa) | Illustrative soil 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). This is an illustrative average-pressure calculation; it does not verify local peak pressure or the suitability of the ground.
Example 2: Illustrative crane-outrigger area. For an assumed 250 kN outrigger reaction and an illustrative target pressure of 50 kPa, average-pressure arithmetic gives an effective area of 250,000 / 50,000 = 5 m². A square with that area has a side of about 2.24 m. This does not establish a safe mat size: the target pressure needs a site-specific ground assessment, and actual outrigger loads, mat strength and stiffness, effective load distribution, settlement, and equipment requirements must be checked.
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? Mass is converted to weight force using standard gravity, 9.80665 m/s². Under this convention, a kilogram corresponds to about 9.81 newtons; the calculation uses the unrounded standard value before dividing force by area.
Should I count all tires or tracks? Yes, if the load is shared evenly. Choose a footprint task and enter a whole count of identical rectangular contact patches. The calculator multiplies one patch’s area by that count. If the load is not shared evenly, calculate each contact patch separately.
How does ground pressure compare to soil bearing capacity? Compare the calculated average pressure with a site-specific allowable bearing pressure determined for the actual ground, loading, and effective support area. The generic ranges above are not site ratings. Bearing failure, settlement, load distribution, and mat strength and stiffness also matter. For U.S. construction crane work covered by OSHA’s crane rule, ground preparation and supporting materials must satisfy the equipment manufacturer’s support and level requirements; this calculator does not establish that compliance.
