Footing Bearing Pressure Calculator
This calculator determines the net bearing pressure beneath a concentrically loaded spread footing and compares it to an allowable soil bearing capacity. The bearing pressure q = P / A, where P is the total service load on the footing (column load plus footing self-weight) and A is the footing base area (length x width). Checking that the actual bearing pressure does not exceed the allowable capacity is a fundamental geotechnical serviceability check. The allowable bearing capacity must come from a site-specific geotechnical investigation; typical values are provided as guidance only.
Bearing pressure formula
q = P / (B × L)
Utilisation = q / qa × 100%
Status: OK if q ≤ qa
P is the total vertical service load, B and L are the footing plan dimensions, and qa is the allowable soil bearing capacity from the geotechnical report.
Bearing pressure design guidance
- Keep q at or below qa with a suitable factor of safety already embedded in qa (geotechnical allowable values typically include a factor of safety of 2.5-3.0 against bearing failure).
- For eccentric loading (combined axial and moment), check both q_max and q_min and ensure q_min is positive (no uplift) for most soil conditions.
- The footing thickness t must satisfy ACI 318 punching shear and one-way shear requirements independently of bearing pressure.
- Settlement (especially in clays) is often the governing concern and should be assessed by a geotechnical engineer even when bearing pressure is acceptable.
Frequently asked questions
What is bearing pressure under a footing?
Bearing pressure is the contact stress between the bottom of a footing and the soil beneath it. It equals the total vertical load on the footing divided by the footing base area (q = P / A for a concentric load). The allowable bearing capacity is set by a geotechnical engineer from site investigation data.
What is the difference between gross and net bearing pressure?
Gross bearing pressure includes the weight of the footing and overburden soil above it. Net bearing pressure subtracts the effective overburden stress at the footing base level, giving the additional stress imposed on the soil by the structure. Allowable bearing capacities from geotechnical reports may be stated as either gross or net; use the matching definition.
How does eccentricity affect bearing pressure?
When the column load is eccentric (the resultant force does not coincide with the footing centroid), bearing pressure is no longer uniform. The maximum pressure is q_max = P/A + M/S, where M is the moment and S is the footing section modulus. The resultant must stay within the middle third of the footing to avoid tension (uplift).
What are typical allowable soil bearing capacities?
Loose sand: 1,000-2,000 psf; dense sand: 3,000-6,000 psf; stiff clay: 1,500-3,000 psf; hard rock: 20,000-100,000 psf. Always use site-specific values from a geotechnical investigation, not generic tables.
What code governs footing design?
ACI 318 Chapter 13 governs concrete spread footings in US construction. ASCE 7 Chapter 18 addresses geotechnical investigation requirements. Local building codes (IBC) reference both and may add requirements for specific soil conditions.
Official sources
- American Concrete Institute: ACI 318 Building Code Requirements for Structural Concrete, Chapter 13.
- American Society of Civil Engineers: ASCE 7 Chapter 18 Soils and Foundations.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.