Soil Bearing Capacity Calculator
Will the soil hold your footing? Enter the load and footing size and this tells you the footing area you need, the actual bearing pressure, and whether it passes the soil’s allowable capacity.
Will the Soil Hold Your Footing?
Every foundation pushes down on the soil, and every soil has a limit to how much pressure it can take before it settles or fails. The question is simple: is your footing big enough to spread the load so the pressure stays under that limit? The math is just as simple:
Spread a bigger load over a bigger footing and the pressure drops. This calculator gives you the area you need, the pressure your chosen footing actually puts on the soil, and a clear pass or fail.
Typical Allowable Bearing Values
When you do not have a soil report, building codes list presumptive allowable values by soil type. These are conservative starting points:
| Soil / rock | Allowable (psf) | Allowable (kPa) |
|---|---|---|
| Clay, silty clay | 1500 | 72 |
| Sand, silty sand | 2000 | 96 |
| Sandy gravel, gravel | 3000 | 144 |
| Sedimentary rock | 4000 | 192 |
| Crystalline bedrock | 12000 | 575 |
Sizing the Footing
Once you know the required area you can pick dimensions. A square footing of side √area is the most compact; a strip footing under a wall trades width for length. The calculator reports the minimum square size so you have a quick target, then lets you test the actual length and width you plan to pour.
Frequently Asked Questions
Allowable or ultimate capacity?
The presumptive table values are already allowable, so leave the safety factor at 1. If you have an ultimate capacity from a geotechnical report, enter it and set the safety factor (often around 3) to get the allowable.
Do I still need a soil report?
For decks, sheds and small pads the presumptive values are usually accepted. For a house or anything heavy or on questionable ground, a geotechnical investigation is the right call and may be required.
Does this cover settlement and frost?
No – this is a bearing-pressure check only. Footings must also reach below the frost line and be checked for settlement, frost heave and overturning where they apply.
Related calculators
- Footing Size Calculator — turn the required area into footing dimensions.
- Concrete Slab Calculator — concrete for the slab above.
- Post Hole Calculator — concrete for deck posts and piers.
- Concrete Calculator — total concrete volume and bags.
- Bearing Stress Calculator — the machine-part version, for bolts and pins.