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Load ÷ soil = width. The prescriptive math, done right.
Footing sizing starts with one division: the load divided by what the soil can bear. This calculator runs that math for continuous wall footings and column pads, applies the prescriptive thickness rules (thickness ≥ projection, 6" minimum), and shows the projection each side. Soil capacity presets cover soft clay through bedrock — but the number that matters is the one from your site.
Owner-builders and garage/shed builders use this to size footings from load and soil before the building department asks; contractors use it as a five-second prescriptive check. It deliberately says when to stop calculating and call an engineer — that honesty is the feature.
Load per foot ÷ soil bearing. A typical two-story wall carrying 3,000 lb/ft on 2,000 psf soil needs 1.5 ft — an 18-inch footing, 6 inches thick. The IRC prescriptive minimum for light one-story construction on good soil is 12"×6".
Multi-story construction, retaining walls, poor or unknown soils, steep sites, seismic zones D–F, and anything the building department stamps. Prescriptive math covers conventional light-frame work on decent soil; everything else is engineered.