Concrete Volume Calculator
Cubic yards or cubic metres of concrete needed for a slab, footing, or pad
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What this calculator computes
Concrete volume calculation is the foundation of every concrete-pour project, from a small backyard patio to a large commercial slab, because under-ordering forces a second delivery at substantial premium and over-ordering wastes material that cannot be returned. The calculator takes three primary inputs — length, width, and depth — and outputs the volume in cubic yards (the standard US ready-mix unit), cubic metres (the standard metric ready-mix unit), and the equivalent number of 60 lb or 80 lb bags for small projects below the ready-mix minimum. US ready-mix concrete is typically sold by the cubic yard with a 1 cubic-yard minimum order from most suppliers and a short-load surcharge below 5 cubic yards; metric ready-mix is sold by the cubic metre with similar minimums. The calculator also adds a recommended waste factor (5–10% for typical slabs, more for irregular pours and footings with high spillage risk) so the order quantity covers form-leakage, rough-edge fills, and the unavoidable losses at chute and pump-truck handoff. Common applications include patio slabs (typically 3.5–4 inches thick), driveway slabs (4–6 inches), garage and shop floors (4–6 inches with reinforcement), foundation footings (typically 12–24 inches deep depending on frost line), and fence-post setting (small per-post volumes that aggregate quickly).
Calculator
The formula
Formula
V = L × W × D (rectangular); V = π × r² × D (circular pier or post hole)
Worked example
When to use this calculator
Use this calculator at the planning stage for any concrete pour, before ordering ready-mix or buying bagged concrete from the home-improvement store. Small projects under 1 cubic yard (about 27 cubic feet) are typically done with bagged concrete because the ready-mix minimum order makes delivery uneconomical, while projects above 1 cubic yard cross the ready-mix break-even point and benefit from delivered concrete in cost, consistency, and finish quality. The calculator is also useful for sanity-checking a contractor's quoted material quantity, since over-quoting concrete is a common practice in residential bid markup. It does not substitute for engineered structural-concrete specifications in foundation, retaining-wall, or load-bearing-slab work, where mix design, reinforcement, and curing protocols matter as much as raw volume.
Common input mistakes
- Forgetting to convert depth from inches to feet before multiplying. A 4-inch slab depth must enter the calculation as 0.333 ft (or as 0.0333 yards), not as 4. Failing to convert produces a result 12× larger than the actual volume, leading to drastically over-ordering ready-mix.
- Skipping the 5–10% waste factor. Real-world pours lose concrete to form-leakage, chute spillage, rough-edge fills, and the inevitable last-pour material that ends up in the wheelbarrow rather than the slab. A pour calculated to exactly 2.0 cubic yards of net volume needs roughly 2.1–2.2 cubic yards ordered to finish cleanly without a costly second delivery.
Frequently asked questions
How many 80 lb bags of concrete make a cubic yard?
One 80 lb bag of standard concrete mix yields about 0.6 cubic feet of finished concrete, so a cubic yard (27 cubic feet) requires approximately 45 bags. A 60 lb bag yields about 0.45 cubic feet, requiring 60 bags per cubic yard. For projects above about 30 bags, ready-mix delivery is usually more economical despite the minimum-order surcharge because the labour savings and consistent mix outweigh the bagged-concrete cost premium.
What is the typical ready-mix concrete order minimum?
Most US ready-mix suppliers have a 1 cubic-yard minimum order with a short-load surcharge for any delivery below approximately 5 cubic yards. The surcharge typically ranges from $50 to $200 per yard short of 5, varying by supplier and market. Below 1 cubic yard, ready-mix is rarely economical, and bagged concrete from a home-improvement store becomes the standard option despite the higher per-cubic-foot material cost.
How thick should a concrete slab be?
Patio and walkway slabs are typically 3.5 to 4 inches thick over a compacted gravel base; driveway slabs handling vehicle loads run 4 to 6 inches with welded-wire fabric reinforcement; garage and shop floors are usually 4 to 6 inches with reinforcing steel. Foundation slabs and load-bearing slabs follow engineered specifications that depend on soil bearing capacity, applied loads, and local frost-line requirements rather than rules of thumb.
How much waste should I add to my concrete order?
Add 5–10% waste for typical rectangular slabs poured into well-built forms, where most loss comes from form-leakage and chute spillage. Add 10–15% for irregular shapes, footings with rough form sides, and pours that involve hand-placement rather than chute-direct flow. Add 15–20% for footings with rebar congestion, irregular footings around obstructions, and any pour where the placement crew is inexperienced with the mix.
How do I convert cubic yards to cubic metres?
One cubic yard equals 0.7646 cubic metres, so multiply your cubic-yard figure by 0.7646 to get cubic metres. A 5 cubic-yard order is approximately 3.82 cubic metres; a 10 cubic-yard order is 7.65 cubic metres. The conversion is exact and traces back to the cubic-foot-to-cubic-metre relationship: 1 cubic yard = 27 cubic feet, and 1 cubic foot = 0.02832 cubic metres.