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Learn how to design a simple residential concrete spread footing in Calcs.com, including specifying soil properties, load, footing size, and reinforcement.

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Sliding check: what the calculator models

The Spread Footing calculator (ACI 318-14, ACI 318-19, and IBC 2024 versions) computes sliding resistance using base friction only: Sliding resistance = μ × (P + W_f) where μ is the lateral sliding coefficient between concrete and soil, P is the ASD axial load, and W_f is the factored footing and soil self-weight. The sliding demand vs. resistance breakdown is shown when the results section is expanded.
Passive earth pressure is not modeled as a resistance term. There are no inputs for a passive pressure coefficient, embedment depth for passive resistance, or soil shear strength, and it is not listed in the assumptions.
If passive pressure is a significant contributor to sliding resistance for your design, you’ll need to evaluate it separately outside the calculator and combine it manually with the calculator’s friction resistance.

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See the exact clause

Every check in this calculator links back to its governing clause in ACI 318-14. Open the Formula Reference panel on any result and select the clause reference to read it — see Viewing Clauses from Inside a Calculator.