Concrete Volume & Bags
Concrete volume for a slab or a round hole, a waste allowance, and the bag count from a manufacturer-stated yield or your own — with the rounding shown.
Volume first,
then bags you can name.
How the volume is formed, where the bag yield comes from, and what this estimate does not decide.
Volume and waste
A slab is length × width × thickness; a round hole or column is π × (diameter ÷ 2)² × depth, treated as solid — a post standing in the hole is not deducted. Every dimension is converted to metres first (1 ft = 0.3048 m, 1 in = 25.4 mm exactly), so the cubic metres, litres, cubic feet and cubic yards shown are the same quantity, not separate estimates. The order volume adds your waste allowance to the whole volume; the allowance is yours to set for the job — the page does not assume one.
Where the bag count comes from
Bags = order volume ÷ yield per bag, rounded up, and the page shows the exact quotient and the surplus so the rounding is visible. There is no universal "bags per yard": yield depends on the product and the bag. The ready-made choices quote two manufacturers' own data sheets — QUIKRETE Concrete Mix No. 1101 (40–80 lb bags, data sheet revised October 2022) and Blue Circle Multi-Purpose Concrete (20 kg bag, technical information December 2023) — each labelled by the manufacturer as approximate. For any other product, enter the yield printed on its bag or data sheet. Without a yield, no bag count is shown.
What this does not decide
This is a quantity estimate. It does not choose or check slab thickness, concrete strength, reinforcement, sub-base, footing size, or compliance with any building code — take those from your design or local requirements. Actual yield varies with water, compaction and spillage; delivered ready-mix is usually ordered in supplier increments not shown here. Prices are whatever you enter. Inputs stay in your browser; the same four anonymous usage counts as the rest of the site apply.