Spread Footing

Isolated column footing — soil bearing, one/two-way shear, flexure (ACI 318).

Enter service (unfactored) loads — the tool applies the 1.2D + 1.6L strength combination internally. Allowable soil bearing q_allow is a geotechnical (service-level) input from the soils report.

Design diagram — updates live with your inputs

Column & Loads

Column dead load (lb) Service

Column live load (lb) Service

Column width c1 (in)

Column depth c2 (in)

Footing & Soil

Allowable soil bearing (psf) From the geotechnical report

Footing size (square) (ft)

Footing thickness h (in)

Concrete & Reinforcement

Concrete f'c (psi)

Reinforcement fy (psi)

Bar size Each-way bottom mat

Bars each way

Clear cover (in) 3 in cast against earth

ACI 318-19 / IBC 2021

Validation, assumptions & limitations Download validation report (PDF) ↗

This calculator is verified by 4 independent tests comparing its output against closed-form statics, NDS/SDPWS design-standard values and published worked examples. Full case-by-case results are in the PDF report.

Assumptions

Concentric column on a square footing; rigid footing, uniform soil pressure; normalweight concrete (lambda=1.0).
phi: shear 0.75, flexure 0.90 (ACI Table 21.2.1); 3 in cover.
Strength loads 1.2D+1.6L for concrete; service loads for soil bearing.

Limitations

Allowable soil bearing is a geotechnical INPUT (not derived) — confirm with the soils report.
Concentric load only (no moment/eccentric bearing); square footing.
Development length / dowel detailing not checked.

Results are for preliminary design and must be confirmed by a licensed engineer against the current adopted code and project-specific conditions.