Presumptive Bearing Capacity Values
The starting point of every footing conversation: what the ground can be presumed to carry before anyone has drilled or tested anything.
| Sound bedrock | 1000 kPa and up, often far more |
| Weathered or fractured rock | 300 to 1000 kPa |
| Dense gravel, sand and gravel | 300 to 600 kPa |
| Medium dense sand | 100 to 300 kPa |
| Loose sand | under 100 kPa |
| Stiff to very stiff clay | 150 to 300 kPa |
| Firm clay | 75 to 150 kPa |
| Soft clay, silt, organics | under 75 kPa, engineered solution territory |
| Conversion | 100 kPa is about 2000 psf |
Notes for design and site
Presumptive means exactly that: code starting values for preliminary sizing and for small structures where an investigation is not warranted. They assume level ground, footings at sensible embedment, and no groundwater surprises. Local codes publish their own tables and those govern where they apply; the ranges here are the common envelope those tables live inside.
What actually controls is worth knowing. Sands are usually settlement governed: the allowable pressure is often the value that keeps settlement near 25 mm, not the one that avoids shear failure, and a water table within a footing width of the base can roughly halve capacity. Clays add long term consolidation to the story. The moment the structure matters, the presumptive number is what you design the site investigation around, not the footing.
Related Calculators and Reference
- Terzaghi Bearing Capacity Calculator: the real calculation these values stand in for.
- Isolated Footing Sizing Calculator: turn an allowable pressure into a footing.
- Pile Bearing Capacity Estimator: for the ground at the bottom of this table.
- Terzaghi Bearing Capacity Equation: the theory page behind the calculator.
- Unit Weight of Soil: the companion table for overburden.
- Federal Highway Administration: geotechnical engineering publications.