Estimate concrete volume, bags, and ready-mix order size for slabs, footings, post holes, and known volumes.
Use the bag count for small pours, hand-mixed work, or retail concrete mix. Use the ready-mix order when the volume is larger or when a supplier sells by cubic yard, cubic meter, or minimum delivery amount. The bag yield should come from the product label.
Formula: rectangular volume = length x width x thickness; round-hole volume = pi x radius squared x depth x quantity; known volume is multiplied by quantity. The calculator adds the extra margin, then rounds bags by mixed bag yield and ready-mix by the supplier order step.
Reference examples: in metric units, a 3 m x 2 m pour at 10 cm thick with 10% extra needs 0.66 m³, or 660 L, which is 66 bags at 10 L per bag and 0.7 m³ of ready-mix with a 0.1 m³ supplier order step. In US units, a 12 ft x 10 ft slab at 4 in thick needs about 1.63 cu yd, or 74 bags at 0.6 cu ft per bag and 1.75 cu yd of ready-mix with a 0.25 cu yd supplier order step.
Measure inside the forms and use the mixed yield printed on the bag. Uneven sub-base, over-excavation, form movement, spillage, and supplier minimums can change the final order. This page estimates quantity only; it does not size reinforcement, strength, slab thickness, or structural footings.
Sources support the volume method, bag-yield assumptions, small-project concrete use, curing and product limitations, and Portland cement safety context.
Use these related calculators before planning concrete base, surface, or finishing materials.
Last reviewed: 6/24/2026