NumberTally Concrete Calculator
How much concrete for a slab, patio, or footing? Enter the dimensions to get cubic feet, cubic yards (what you order), and exactly how many bags you’ll need — with an optional waste allowance so you don’t run short.
Bags vs ready-mix: which should you choose?
Bagged concrete makes sense up to about 1 cubic yard (roughly 45 eighty-pound bags). Beyond that, ready-mix delivery is usually cheaper and far less labor — but most suppliers charge a short-load fee under 3–4 yards, so small pours still favor bags. This calculator shows both so you can compare.
Tips for ordering concrete
Always round up: running short mid-pour creates a cold joint that weakens the slab. The 5% waste allowance covers spillage and uneven subgrade; use 10% if the ground is rough. Order ready-mix in quarter-yard increments, and have wheelbarrows and help ready — concrete waits for no one.
Frequently Asked Questions
How many 80 lb bags of concrete make a cubic yard?
One cubic yard is 27 cubic feet, and an 80 lb bag yields about 0.6 ft³ — so 45 bags per yard. A 60 lb bag yields 0.45 ft³ (60 bags per yard); a 40 lb bag yields 0.3 ft³ (90 per yard).
How thick should a concrete slab be?
4 inches is standard for patios, walkways, and shed floors. Driveways and garage floors need 5–6 inches; anything carrying heavy equipment should be 6+ inches with rebar.
How do you convert cubic feet to cubic yards?
Divide by 27 — there are 27 cubic feet in a cubic yard (3 × 3 × 3). Ready-mix is always sold by the cubic yard.
Should I add extra concrete for waste?
Yes — 5% is the standard allowance for spillage, form leakage, and minor over-excavation. It’s far cheaper than a second delivery for half a yard.
How much does a yard of concrete weigh?
About 4,000 lb (2 tons). That’s why anything over a yard or two is a ready-mix job — 45 eighty-pound bags weigh 3,600 lb before you even add water.