Enter Footing and Load Details
Formula Used
1) Total service load: W = Dead Load + Live Load + Footing Self Weight
2) Plan area: A = B × L
3) Average gross soil pressure: qavg = W / A
4) Corner pressure under biaxial eccentricity: q = qavg × (1 ± 6ex/B ± 6ey/L)
5) Effective dimensions: B' = B - 2ex and L' = L - 2ey
6) Effective area pressure: qeff = W / (B' × L')
7) Net bearing pressure: qnet = qavg - γDf
Here, γ is soil unit weight and Df is foundation depth. A safe result usually means the maximum contact pressure stays below the allowable value and the minimum pressure remains nonnegative.
How to Use This Calculator
- Select metric or imperial units.
- Enter dead load, live load, and footing self weight.
- Provide footing width, footing length, and foundation depth.
- Enter soil unit weight and allowable bearing pressure.
- Add eccentricities in both directions if the load is off-center.
- Press the calculate button to view bearing pressure results above the form.
- Review maximum pressure, minimum pressure, utilization, and the graph.
- Export the output as CSV or PDF for reporting.
Example Data Table
| Case | Dead Load (kN) | Live Load (kN) | Footing Weight (kN) | B (m) | L (m) | ex (m) | ey (m) | Allowable (kPa) | qmax (kPa) |
|---|---|---|---|---|---|---|---|---|---|
| Example A | 600 | 250 | 80 | 2.5 | 3.0 | 0.05 | 0.03 | 250 | 142.26 |
| Example B | 720 | 220 | 95 | 2.8 | 3.2 | 0.04 | 0.02 | 280 | 126.30 |
| Example C | 500 | 180 | 70 | 2.2 | 2.8 | 0.06 | 0.04 | 220 | 134.06 |
Frequently Asked Questions
1) What is soil bearing pressure?
Soil bearing pressure is the contact stress transferred from a footing to the supporting soil. Designers compare it with the allowable bearing capacity to keep settlements and shear failure within acceptable limits.
2) What is the difference between gross and net pressure?
Gross pressure is the average footing load divided by footing area. Net pressure removes the overburden stress that existed before construction, so it better represents the additional stress caused by the foundation.
3) Why do eccentricities matter?
Eccentric loading makes pressure uneven across the footing. One side carries more stress while the opposite side carries less. Large eccentricity can even produce tension, meaning part of the footing may lose contact with soil.
4) What does “within kern” mean?
It means the load resultant stays inside the middle third of the footing in both directions. When this happens, soil contact remains compressive over the whole base, and the corner pressure equations behave more reliably.
5) When should I use effective area pressure?
Use effective area pressure when eccentricity reduces the compression zone. It offers a practical estimate of stress on the remaining contact area, especially when the load approaches or passes the kern boundary.
6) Is this calculator suitable for final structural design?
It is helpful for preliminary sizing, quick checking, and reports. Final design should still consider settlement, code requirements, groundwater, layered soil behavior, load combinations, and geotechnical recommendations.
7) What allowable pressure should I enter?
Enter the allowable bearing pressure provided by the geotechnical report or by your approved design basis. Using assumed values without soil data can lead to unsafe or overly conservative results.
8) What should I do if the result is unsafe?
Increase footing area, reduce eccentricity, lower service loads, improve the soil, or revise the foundation type. Recheck both maximum pressure and minimum pressure after every change.