Soil Bearing Pressure Calculator

Inputs

Example data table

How to use

1. Select design state (service or ultimate) and enter loads.
2. Choose footing shape and enter dimensions.
3. Enter soil unit weight, embedment depth, and surcharge if any.
4. Optional: add eccentricity (ex/ey) or moments (Mx/My).
5. Optional: provide allowable bearing or ultimate + FS for pass/fail.
6. Press Calculate. Download results as CSV or PDF.

Technical article

1) What bearing pressure represents

Bearing pressure is the average contact stress transmitted from a footing to soil. It is reported in kPa, where 1 kPa equals 1 kN/m². Preliminary sizing often targets stress levels that keep settlement and shear failure risks low, then confirms with a site investigation. Common residential footings may see loads from 300 to 1500 kN, so checking stress helps avoid excessive differential settlement early during layout changes.

2) Gross versus net pressure

Gross pressure uses the full applied load divided by area. Net pressure subtracts overburden and surcharge: q_over = γ·Df + q_s. For example, with γ = 18 kN/m³ and Df = 1.2 m, overburden is about 21.6 kPa before any surcharge is added.

3) Load components and design states

The calculator accepts a single total load or a breakdown of dead, live, and equipment loads. In ultimate state, user factors are applied to each component or to the total. This helps compare service-level stresses with factored demand used in strength-oriented checks.

4) Footing geometry and area

Area depends on shape: A = B·L for rectangular or strip footings, A = πD²/4 for circular. A 2.0 m by 3.0 m footing has A = 6.0 m², while a 2.2 m diameter pad has about 3.80 m². Larger area lowers average stress.

5) Eccentricity and pressure distribution

When loads are offset, contact stress becomes non-uniform. For rectangular footings the corner equation is q = (P/A)(1 ± 6ex/B ± 6ey/L). The tool reports q_max and q_min and flags negative q_min, which indicates uplift and likely partial contact.

6) Embedment, groundwater, and surcharge

Embedment increases overburden and can improve stability, but it reduces net pressure. If groundwater affects effective unit weight, selecting γ′ approximates buoyant conditions. Typical total unit weights range from 17 to 20 kN/m³, while saturated effective values can be much lower.

7) Allowable capacity and utilization

Enter q_allow directly or provide q_ult and a factor of safety so q_allow = q_ult/FS. Many shallow foundations use allowable values in the 100–300 kPa range, depending on soil and settlement limits. Utilization is applied/allowable; values above 1.0 indicate failure.

8) Reading warnings and next steps

Warnings highlight unit mistakes, very small areas, high stresses, or eccentricities beyond B/6 or L/6. Use the results to compare alternatives, then confirm with bearing capacity, settlement analysis, and detailing. Final design should follow local codes and a geotechnical report.

FAQs

1) What is the difference between gross and net bearing pressure?

Gross pressure is P/A. Net pressure subtracts overburden and surcharge: q_net = P/A − (γ·Df + q_s). Net is useful when comparing to net allowable values reported by a geotechnical study.

2) When should I use service versus ultimate state?

Use service for settlement-sensitive checks and typical allowable bearing comparisons. Use ultimate when you want factored demand using your chosen load factors. Always match the approach to your design standard and project requirements.

3) How do moments relate to eccentricity?

For a vertical load P, eccentricity is derived from moments: ex = My/P and ey = Mx/P. The tool converts your moments to equivalent offsets, then estimates corner pressures for rectangular footings.

4) What does negative qmin mean?

A negative minimum pressure implies tension at part of the base, which soil cannot resist. This suggests uplift and partial contact. Recheck eccentricity, increase footing size, or adjust load placement and structural layout.

5) How do I choose soil unit weight and embedment depth?

Use values from your site data when available. Typical total unit weights are about 17–20 kN/m³. Embedment depth Df should reflect finished grade to footing base. If groundwater is important, select the effective unit weight option.

6) Can the calculator replace a geotechnical report?

No. It provides preliminary stress and comparison checks. Actual allowable bearing and settlement limits depend on stratigraphy, groundwater, and testing. Use this tool to screen options, then finalize using professional geotechnical recommendations.

7) What capacity value should I compare against?

Use q_allow from your geotechnical report when possible. If only ultimate capacity is known, compute allowable with FS: q_allow = q_ult/FS. Comparing against net maximum pressure is a conservative choice for eccentric loading.