What is the Bearing Capacity Calculator?
Calculate ultimate and allowable soil bearing capacity with this free bearing capacity calculator using Terzaghi's equation. Choose strip, square, or circular footings. Enter cohesion c, friction angle φ, unit weight γ, foundation depth D, and footing width B. Get q_ult, q_allow = q_ult/FS, bearing factors Nc/Nq/Nγ, term breakdown, and optional applied pressure check. Soil presets for sand and clay. Metric (kPa, kN/m³, m) and imperial (psf, pcf, ft). Runs instantly in your browser.
How to use the Bearing Capacity Calculator
- Select strip, square, or circular footing type.
- Choose metric or imperial units.
- Enter soil properties c, φ, γ and footing depth D and width B.
- Set safety factor FS (default 3) and optional applied bearing pressure.
- Review q_ult, q_allow, factor breakdown, and calculation steps.
Common use cases
- Preliminary sizing of a spread footing on sand or clay
- Checking whether applied column pressure is below q_allow
- Geotechnical homework on Terzaghi bearing factors
- Comparing strip vs square footing capacity for the same soil
- Quick estimate before detailed foundation design
Frequently asked questions
- What is bearing capacity?
- Bearing capacity is the maximum pressure a foundation can exert on soil without shear failure. Ultimate capacity q_ult is divided by a safety factor FS to get allowable bearing pressure q_allow for design.
- What is Terzaghi's bearing capacity equation?
- q_ult = c·Nc·sc + γ·D·Nq·sq + ½·γ·B·Nγ·sγ, where Nc, Nq, Nγ depend on friction angle φ and sc, sq, sγ are shape factors for square or circular footings.
- What safety factor should I use?
- FS = 3 is common for shallow foundations in many codes. Higher FS (3–4) applies for sensitive structures or uncertain soil data. This tool lets you compare FS = 2, 2.5, 3, or 4.
- What about φ = 0 clay?
- For undrained clay, set φ = 0°. The calculator uses Nc = 5.14, Nq = 1, Nγ = 0, so q_ult ≈ 5.14·c·sc plus the depth term γ·D.
- Is this a substitute for a geotechnical report?
- No. This uses classic Terzaghi theory with shape factors. Real projects need site investigation, groundwater, layering, and code-specific methods (e.g. Hansen, Meyerhof). Use for estimates and learning.
