What is ground bearing capacity?

Ground bearing capacity is the maximum pressure the soil can support without excessive settlement or failure. It varies by soil type: soft clay ~50 kN/m², firm clay ~100 kN/m², stiff clay ~150 kN/m², medium sand ~200 kN/m², dense gravel ~300 kN/m². These are ultimate values — a safety factor of 2.5-3.0 is applied to get the allowable bearing pressure.

How do I calculate foundation pressure?

Foundation pressure = Total Load / Foundation Area. For example, a wall load of 50 kN/m on a 600mm wide strip foundation applies 50 / 0.6 = 83 kN/m² pressure. This must be less than the allowable bearing capacity of the soil. If it exceeds the capacity, widen the foundation or use a different foundation type (raft, piles).

How is allowable bearing pressure determined?

Allowable bearing pressure = Ultimate bearing capacity / Safety factor. The safety factor is typically 2.5-3.0. Additionally, surcharge relief (the weight of soil above foundation level) can be added. A geotechnical investigation (trial pits, boreholes) determines the actual soil bearing capacity for your specific site.

What happens if bearing pressure is exceeded?

If the applied pressure exceeds the allowable bearing capacity, the foundation will settle excessively or the soil will fail, causing structural damage. Solutions include: widening the foundation, deepening to a stronger stratum, using a raft foundation to spread loads, or piling through weak soil to a bearing layer below.

Do I need a ground investigation?

Yes, for any significant building project. While presumed bearing values (from tables) can be used for simple domestic work, a ground investigation (trial pits or boreholes with soil testing) is essential for accurate design. The investigation identifies soil type, bearing capacity, groundwater level, sulphate content and any contamination.

TradeCalculator

Ground Bearing Calculator — Load vs Allowable Pressure

Check if foundation pressure is within allowable ground bearing capacity for your soil type.

Total Load

Total factored load on foundation

Soil Type

Ultimate: 100 kN/m²

Foundation Length

Foundation Width

Foundation Depth

Depth below ground level

How We Calculate This

This calculator checks whether the foundation pressure from your building load is within the allowable bearing capacity of the soil.

Bearing check

Applied Pressure = Total Load / Foundation Area
Allowable = (Ultimate Capacity / Safety Factor) + Surcharge
If Applied ≤ Allowable, the foundation is adequate.

Required width

Min Width = Total Load / (Foundation Length × Allowable)
This gives the minimum foundation width needed if the current width is insufficient.

Frequently Asked Questions

Related Calculators

Concrete Volume Calculator

Calculate concrete volume in m³ for foundations, slabs and paths.

Concrete Mix Calculator

Work out cement, sand and aggregate ratios for different concrete mixes.

Block Calculator

Calculate how many concrete blocks you need per m² of wall.

Brick Calculator

Work out how many bricks you need for walls, piers and features.

Mortar Calculator

Calculate sand and cement quantities for bricklaying and blockwork mortar.

Last updated: March 2026

All calculations are estimates. Verify with your supplier.