Foundation Bearing Calculator

About the Foundation Bearing Calculator

Calculates the minimum footing area needed to support a load on soil of a given allowable bearing capacity, and the size of a square footing.

How to use this calculator

1. Enter the total load on the footing, in units such as \(N\) or \(lb\).
2. Enter the soil bearing capacity, in \(N/m^2\), \(kPa\), or another consistent pressure unit.
3. Read the required footing area the calculator gives, in \(m^2\), \(ft^2\), or the matching area unit.
4. Compare the result with your planned footing size to see whether it is large enough.

The formula explained

The formula \(area = \frac{load}{bearing\ capacity}\) computes the minimum footing area needed to support a load on soil. It works because area must grow when load increases, and area must also grow when soil can support less pressure.

• area = the required footing area
• load = the total force applied to the soil
• bearing capacity = the maximum soil pressure the ground can safely support

Step by step method

1. Write down the load and the soil bearing capacity in consistent units.
2. Divide the load by the bearing capacity to find the required area.
3. Check that the units simplify to an area unit, such as \(m^2\) or \(ft^2\).

Worked example

Problem. A footing must support a load of \(18{,}000\) \(N\), and the soil bearing capacity is \(6{,}000\) \(N/m^2\). Find the required footing area.

1. Use the formula \(area = \frac{load}{bearing\ capacity}\).
2. Substitute the values, \(area = \frac{18{,}000}{6{,}000}\).
3. Compute the result, \(area = 3\).

Tips and common mistakes

• Make sure the load and bearing capacity use compatible units before dividing, because mixed units can give a wrong answer.
• This calculation gives the minimum area, so real designs often include a safety margin and local code requirements.

Frequently asked questions