About this tool Size shallow foundations from applied load and allowable bearing capacity. The calculator determines the required footing width, checks the actual bearing pressure including concrete self-weight and overburden surcharge, and gives a concrete order volume with waste allowance.
Three footing types are supported: square pad (single column), rectangular pad (with a user-defined length/width ratio), and continuous strip (under a wall). The bearing pressure utilisation is colour-coded — green when within capacity, amber above 90%, and red if overstressed.
This goes beyond basic footing volume calculators by working backwards from the engineering requirement: give it a load and bearing capacity, and it tells you how big the footing needs to be.
How to use this tool 1. Select the footing type — square pad, rectangular pad, or strip footing.
2. Enter the applied load — column load in kN for pad footings, or line load in kN/m for strip footings.
3. Enter the allowable bearing capacity — in kPa, from your site investigation report. Typical values are shown below the input.
4. Enter the footing depth — the thickness of the concrete element in metres.
5. Review the results — check the required width, bearing pressure utilisation, and concrete order volume.
A_required = P / (q_a − γ × D)
Where P = applied load, q_a = allowable bearing capacity, γ = soil unit weight (assumed 18 kN/m³), D = footing depth. The net allowable bearing pressure deducts overburden surcharge from the gross allowable capacity.
The bearing pressure check adds concrete self-weight (2,500 kg/m³ per EN 1991-1-1) to the applied load and divides by the footing area. Utilisation is expressed as a percentage of the gross allowable bearing capacity.
Limitations Concentric loading is assumed — no eccentricity or moment loading. For eccentric loads, the effective area method (Meyerhof) should be used, which this tool does not implement.
The tool sizes footings for bearing pressure only. It does not check structural capacity (punching shear, bending reinforcement) — these require a separate structural design check.
Overburden unit weight is assumed at 18 kN/m³. For sites with significantly different overburden (e.g. lightweight fill or heavy made ground), adjust the allowable bearing capacity accordingly.
Revision history 28 April 2026: Initial release
Disclaimer This tool is provided for educational and general information purposes only. It is not a substitute for professional engineering advice, design or verification.
Diggy and its contributors are not licensed engineering consultants and no results generated by this tool should be used directly for construction, design or safety-critical decisions.
All values and outputs are based on published empirical correlations and should be independently checked and confirmed by a qualified geotechnical engineer before use.
By using this tool, you accept full responsibility for how you interpret and apply the information provided.
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