Construction
Concrete Calculator
How much concrete do you actually need? Pick the shape, plug in dimensions, and get cubic yards, cubic meters, and a bag count — with optional waste factor.
Pick a shape and enter dimensions.
Rules of thumb
- A standard residential slab is 4 inches thick. Driveways often go 5–6 inches.
- Always order with a 10% waste factor at minimum — spillage, uneven subgrade, formwork over-pour.
- One 80 lb bag ≈ 0.60 ft³, 60 lb ≈ 0.45 ft³, 40 lb ≈ 0.30 ft³ of mixed concrete.
- For anything over ~0.75 yd³ (about 28 80-lb bags), ready-mix beats bags on price and sanity.
- Most plants charge a short-load fee for orders under 3–4 CY. Ask before you order.
- Using a pump? Add ~0.5 CY for what stays in the line.
FAQ
How accurate is this? +
The math is exact. The 10% waste factor is industry standard — you can adjust it. Bag counts round UP because you can't buy half a bag.
What's the difference between concrete and cement? +
Cement is one ingredient. Concrete is the mix: cement + sand + aggregate + water. This calculator is for finished concrete volume.
When should I order ready-mix vs bags? +
Roughly: under 0.75 cubic yards, bags. Over that, ready-mix delivered. A truck holds ~10 yd³ and most plants have a 1 CY minimum plus a short-load fee under 3–4 CY.
Why add pour zones? +
Most real jobs aren't one rectangle. A slab plus footings, a porch slab plus stair pads — add a zone per shape so the order total is right.