Concrete Calculators
Concrete Calculator
Enter the dimensions of your slab, footing, or column and the calculator returns the volume in cubic feet and cubic yards plus a waste-adjusted order quantity — a 10 × 10 ft slab poured 4 inches thick is 33.33 cubic feet, or 1.23 cubic yards, which becomes 1.36 cubic yards with a 10% waste factor, about 62 80-lb bags of pre-mixed concrete.
Concrete volume
Concrete to order
1.36 yd³
33.33 ft³ · 1.23 yd³ before waste · 62 × 80 lb bags
Breakdown
Volume = shape geometry × a disclosed waste factor; 1 cubic yard = 27 cubic feet. Bag counts use standard pre-mixed yields (80 lb ≈ 0.60 ft³). A planning estimate for ordering, not an engineering specification.
About this calculator
A free concrete calculator that turns slab, footing, and column dimensions into the two numbers a pour actually requires: cubic yards to order from a ready-mix supplier, and bag counts if you are mixing from 80, 60, or 40 lb bags. Every result is shown with and without a disclosed waste factor (default 10%), because the geometric volume of the forms is never the quantity you should buy. Everything is computed in your browser from the dimensions you enter — plain volume arithmetic for planning an order, not an engineering specification. Slab thickness, reinforcement, and mix strength for a structural pour are decisions for your local building code and contractor.
How the volume math works
Every pour reduces to a volume formula. A slab is length × width × thickness: a 10 × 10 ft slab at 4 inches (4 ÷ 12 ft) is 33.33 cubic feet. A trench footing is the same rectangular math with the cross-section in inches: 50 ft of footing at 16 inches wide and 8 inches deep is 44.44 cubic feet. A round column is a cylinder, π r² h per column: four 12-inch-diameter columns 4 ft tall total 12.57 cubic feet.
Concrete is ordered by the cubic yard, and one cubic yard is exactly 27 cubic feet — a 3 × 3 × 3 ft cube. Divide cubic feet by 27 and the three examples become 1.23, 1.65, and 0.47 cubic yards. The calculator does both conversions on every result so the supplier's unit and the tape measure's unit never get mixed up.
Why a 5–10% waste factor is standard practice
The formed volume is a lower bound, not the order quantity. Subgrade is never perfectly level, so a "4-inch" slab averages thicker than 4 inches wherever the gravel dips; some mix is lost to spillage, to the chute and wheelbarrow, and to over-excavation at the edges of footings. Running short mid-pour is the expensive failure — a cold joint where a second batch meets half-cured concrete — so adding 5–10% is standard practice across the trade.
The calculator defaults to 10% and lets you change it. On the 10 × 10 ft slab, 1.23 cubic yards becomes 1.30 at 5% waste and 1.36 at 10% — small money compared to a short pour. Use the high end for hand-graded subgrade or irregular excavation, the low end for well-compacted, screeded base over plastic.
Ready-mix truck or bags — the one-yard decision point
One cubic yard is the practical crossover. Below it, bagged mix is usually cheaper and simpler than paying a ready-mix supplier's short-load fee for a small delivery. Above it, bags get punishing fast: a single cubic yard already takes 45 80-lb bags, 60 60-lb bags, or 90 40-lb bags, every one mixed by hand or in a small drum mixer before the earlier batches start to set.
The 10 × 10 ft slab example sits right at the line: 1.36 cubic yards with waste is about 62 80-lb bags — nearly 5,000 pounds of material to haul and mix in one continuous session. That is a ready-mix order for most crews. The driveway-scale pours in the slab view are not even a question: 6 or 7 cubic yards is truck territory, full stop.
How bag yields work
Bag counts use the standard yields published for pre-mixed concrete (QUIKRETE product data, checked 2026-06-10): an 80 lb bag yields about 0.60 cubic feet, a 60 lb bag about 0.45, and a 40 lb bag about 0.30 — a consistent 0.0075 cubic feet per pound. The calculator divides the waste-adjusted volume by the yield and always rounds up, because a pour cannot use 61.1 bags.
Yields are approximate by nature — they vary slightly with how wet the mix is — which is one more reason the waste factor matters when working in bags. The counts here are for ordinary pre-mixed concrete, not mortar, sand mix, or fast-setting post mix, which have their own yields.
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Questions
- Is the concrete calculator free?
- Yes. It is free, needs no account, and calculates in your browser; nothing you enter is uploaded or stored.
- How many cubic feet are in a cubic yard of concrete?
- 27 — a cubic yard is a 3 × 3 × 3 ft cube. Divide cubic feet by 27 to get the cubic yards a ready-mix supplier quotes; a 33.33 ft³ slab is 1.23 yd³.
- How much waste factor should I add to a concrete order?
- 5–10% is standard practice. Uneven subgrade, spillage, and over-excavation all consume mix beyond the formed volume, and running short mid-pour creates a cold joint. The calculator defaults to 10%.
- Is this an engineering specification?
- No — it is a planning estimate of volume only. Slab thickness, reinforcement, mix strength, and footing dimensions for structural work are governed by your local building code, not by a volume calculator.
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