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Terzaghi Shallow Foundation Bearing Capacity Calculator

Estimate a shallow strip footing's ultimate bearing capacity using Terzaghi's classic bearing capacity equation.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax
6.56 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Ultimate bearing capacity

1072.66 kPa

Check your inputs

This gives ULTIMATE bearing capacity — a real design divides this by a factor of safety (commonly 2.5-3.0) to get the allowable bearing pressure, and applies shape/depth/inclination correction factors for non-strip footings, which this simplified strip-footing calculator omits.

Nc
30.14
Nq
18.4
Nγ
22.4

At the values currently entered, the ultimate bearing capacity works out to 1073 kPa. Note that soil cohesion (c) sits at the low end of the range this calculator was checked against, so treat the output as indicative rather than settled. Confidence is moderate: the method is sound, but real materials and site conditions vary. Figures are shown for United States, where IRC 2024 is the governing residential reference; switch the market above if you are building elsewhere.

Add the equipment this sizes

This result is a specification — 1,072.663 kPa — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Terzaghi's general bearing capacity equation: qu = c×Nc + q×Nq + 0.5×γ×B×Nγ, with Nq = e^(π·tanφ)·tan²(45+φ/2), Nc = (Nq−1)·cotφ (Nc=5.14 at φ=0), and Nγ = 2(Nq+1)·tanφ (Vesic's widely used Nγ approximation)

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Frequently asked questions

What is 'ultimate' bearing capacity vs. 'allowable'?
Ultimate bearing capacity is the theoretical failure load; allowable bearing pressure divides this by a safety factor (typically 2.5-3.0) to keep the foundation well within safe working stress — the allowable value is what you'd actually design against.
Why does this formula only apply to strip footings?
Terzaghi's original equation was derived for a continuous (strip) footing — square, rectangular, or circular footings need additional shape correction factors (from Meyerhof, Hansen, or Vesic's extended methods) for accurate results.
What if my soil has both cohesion and friction?
That's exactly what this formula handles — 'c-φ' soils (like stiff clays or silty sands) use all three terms together, unlike purely cohesive (φ=0) or purely granular (c=0) special cases.