Concrete Footing Calculator

Footings are the widened concrete base that spreads the weight of a house, garage, addition, deck or wall over enough soil to stop it settling. There are two common types in residential work: continuous (strip) footings that run under foundation walls and block walls, and isolated pad (spread) footings that sit under individual posts, piers or columns. This calculator handles both in one estimate so you can price a whole foundation in a single step.

Strip footing volume is simply length × width × depth. A typical residential footing under an 8" foundation wall is 16"–20" wide and 8"–10" deep. Under the 2021 IRC (Table R403.1(1)), the minimum footing thickness is 6" and required width depends on the number of stories, the wall type and the allowable soil bearing pressure — a one-story house on 1,500 psf soil can use a narrower footing than a two-story brick-veneer house on the same soil. Every 1" of extra depth on a 120 ft run adds roughly 0.6 cubic yards of concrete for a 16"-wide footing.

Pad footings are usually square: 16" × 16" × 8" for small deck posts, 24" × 24" × 12" for heavier beam posts and porch columns, and 30"–36" square or larger for posts carrying roof or second-floor loads. The bottom of every footing must sit on undisturbed soil below the local frost depth, which ranges from about 12" in the South to 48" or more in northern states.

For 2026 budgeting, ready-mix concrete averages about $150–$185 per cubic yard in most US metros, with short-load fees of roughly $50–$150 when you order under 4–5 yards. #4 rebar costs about $11–$15 per 20 ft stick. Installed by a contractor, residential strip footings typically run $10–$20 per linear foot including excavation, forms, rebar and concrete, while precast or poured pad footings for decks run about $75–$200 each depending on size and access.

Most footing problems come from ordering too little concrete because trench sides were not straight. Earth-formed footings (poured directly against trench walls) almost always use more concrete than the drawings show, so many contractors add 10–15% on top of the calculated volume. Forming the footing with 2× lumber gives a cleaner, more predictable pour but adds labor. Either way, keep rebar up off the dirt on chairs or bricks so it ends up with about 3" of concrete cover.