Site maths
Average bearing pressure
- where
- pressure (kN/m²)
- force (kN)
- contact area (m²)
- pressure (N/mm²)
Explain this equation
This gives the average pressure when a force is spread over a contact area. Use it for a rough idea of the stress under a padstone, a base plate or a load sitting on the ground.
F is the force in kN and A is the contact area in m². p is the average pressure in kN/m². p_N/mm² is the same pressure in N/mm².
Pressure is force divided by the area it acts on. 1 kN/m² is 1000 N spread over 1 000 000 mm², which is 0.001 N/mm², so dividing by 1000 converts between the two.
100 kN on 0.5 m² is 200 kN/m², or 0.2 N/mm². Halving the area doubles the pressure.
Watch out: this is the average only. Real stress is often higher at an edge or under an off-centre load. A designer must check capacity.
Calculate the arithmetic mean pressure from a known force and area.
Enter your values to see the result.
Good to know
Not a structural safety check. Does not consider eccentricity, buckling, load factors, soil or masonry resistance. A designer must assess capacity.
Sources
- Geometry / arithmetic
Estimates are not design approval or British Standards compliance checks. Structural arch, retaining-wall, wind, foundation, lintel and masonry-capacity design are not performed. Use the project engineer’s specification.