Turn slab, footing, column, or stair dimensions into cubic yards with a waste allowance, plus a Bay Area ready-mix delivered cost range and an 80 lb bag equivalent for small pours.
Every result is a planning estimate, not a quote or an engineering determination. Real pricing depends on soil conditions, access, existing structure, engineering requirements, and your jurisdiction’s current fee schedule. For structural questions we coordinate with a licensed engineer — we do not perform engineering ourselves. Get a site-specific estimate before committing to a budget.
Every volume here is calculated in cubic feet, then divided by 27 to get cubic yards, because that is the unit concrete plants sell in. The math is exact. The site is not. Subgrade is never perfectly flat, trench walls slough, forms bow slightly under load, and some concrete stays in the chute and the wheelbarrow. Ten percent is the standard allowance for slabs on reasonable subgrade. Go to 15 percent for footings in loose or caving soil, where the trench inevitably ends up wider than the plan says.
Slab volume is straightforward as long as you measure the finished thickness, not the excavation depth — base rock takes up part of that. Continuous footings need the total run of every leg added together, and the trench depth measured from the bottom of the trench to the top of the form. Round columns and pier holes use the diameter of the hole, which is usually wider than the sonotube nominal size once the auger has done its work. Stairs are the one shape people consistently underestimate: the volume is the stepped wedge, which is roughly half of the box you would draw around it.
For placement, forming, and finishing on real projects, see concrete flatwork and driveways or new home foundations.
About 45. Each 80 lb bag yields roughly 0.6 cubic feet and a cubic yard is 27 cubic feet. Bags make sense for post holes, small pads, and patch work. For anything approaching a full yard, ready-mix is cheaper, faster, and far more consistent in strength.
Always order a little extra. Coming up short mid-pour creates a cold joint where the fresh concrete never bonds to what already set, and that joint is a permanent weak line. A quarter yard of leftover concrete costs under a hundred dollars. A cold joint through a footing can mean demolition.
Residential slabs and footings in the Bay Area typically call for 3,000 to 4,000 psi. Your structural drawings will specify it, along with any fiber, air entrainment, or maximum water-cement ratio. Follow the sheets rather than the plant default, and we coordinate with your licensed engineer if anything on the mix design is unclear.
Partly. Ten percent handles ordinary spillage and minor grade variation. If a footing trench caved or you over-dug to reach firm soil, measure the actual trench and use 15 percent, because that void is filled with concrete whether you planned it or not.
Tell us what you're building — a new home, an ADU, an addition — and we'll get back to you with next steps, usually within one business day.
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