Ordering concrete is unforgiving — too little leaves you short mid-pour; too much means paying for concrete you throw away. Enter your slab dimensions below for cubic yards, bag counts and a cost estimate.
How much concrete do you need?
Enter your slab size to get cubic yards for ready-mix — or the number of 60 lb and 80 lb bags to mix yourself.
Your estimate
Includes your extra allowance for uneven ground, spillage and over-excavation — pros typically add 5–10%. One 80 lb bag yields about 0.6 cubic feet of concrete; one 60 lb bag yields about 0.45 cubic feet. Ready-mix trucks usually have a minimum order and short-load fees under 4–5 yards.
How to use this concrete calculator
- Measure the length and width of your slab, pad or footing.
- Enter the thickness — 4 inches is standard for patios and walkways, 5–6 inches for driveways.
- Keep the 10% extra allowance unless your ground is perfectly level.
- Choose your route: cubic yards for a ready-mix truck, or bag counts if you are mixing yourself.
How we calculate concrete
Volume = length × width × thickness. Cubic yards = cubic feet ÷ 27. For bags: one 80 lb bag yields about 0.6 cubic feet of mixed concrete and one 60 lb bag about 0.45 cubic feet, so bags needed = volume ÷ yield, rounded up. Your extra allowance is added to the volume first, because real ground is never perfectly flat.
Concrete calculator FAQs
How much concrete do I need for a 10×10 slab?
At the standard 4-inch thickness, a 10×10 slab needs about 1.36 cubic yards including a 10% safety allowance — order 1.5 yards of ready-mix to be safe. Mixing it yourself takes roughly 62 bags of 80 lb mix, or 82 bags of 60 lb mix.
How thick should a concrete slab be?
Four inches is standard for patios, walkways and shed bases. Driveways and anywhere vehicles drive or park should be 5–6 inches, ideally with steel reinforcement.
How much area does a cubic yard of concrete cover?
One cubic yard is 27 cubic feet. Poured 4 inches thick it covers about 81 sq ft; at 6 inches thick, about 54 sq ft.
Is ready-mix or bagged concrete better?
For jobs under about 1 cubic yard, bags are usually cheaper and far more flexible. Above that, a ready-mix truck wins on effort and consistency — mixing 60 or more bags by hand is a full day of heavy work.