Concrete Calculator
Work out how much concrete you need for a slab, footing, wall or column — and add several elements for one combined total. Get the volume in cubic yards, the number of 40, 60 or 80 lb bags, a 10% overage and the bag cost. A 10 ft × 10 ft slab at 4 inches is about 1.23 yd³.
1.36 yd³ concrete (incl. 10% waste)
62 bags of 80 lb · 36.67 ft³
Before waste: 1.23 yd³. Ready-mix is usually ordered by the cubic yard; bagged mix suits small pours.
Volumes use standard geometry; bag yields are 80 lb ≈ 0.60 ft³, 60 lb ≈ 0.45 ft³, 40 lb ≈ 0.30 ft³. How we calculate →
How to calculate concrete
Concrete is ordered by volume. For a slab, volume = length × width × thickness with everything in the same unit, then converted to cubic yards (the unit ready-mix is sold in): cubic yards = (L_ft × W_ft × thickness_ft) ÷ 27. A 10 ft × 10 ft slab at 4 inches thick is about 1.23 cubic yards. Pick a shape above, enter the dimensions, and the calculator totals the volume and the number of bags.
Footings, walls and round columns use the same idea with their own formula — the calculator switches the inputs automatically when you change the shape, and you can add several elements to get one combined total.
How many bags of concrete per cubic yard
A cubic yard is 27 cubic feet. An 80 lb bag of pre-mix yields about 0.60 ft³, so a cubic yard takes roughly 45 bags of 80 lb (about 60 bags of 60 lb, or 90 bags of 40 lb). Bagged mix is convenient for small pours like a post or a few footings; for anything approaching a cubic yard or more, ready-mix delivery is usually cheaper and easier.
Always order a little extra
Forms bulge, subgrades are uneven and some concrete is always lost, so order about 10% extra — the calculator adds your chosen waste factor. Running short mid-pour means a cold joint or a second delivery, so it's worth the small overage.
Slabs, footings, walls and columns
A slab or footing is length × width × thickness. A wall is length × height × thickness. A round column or pier is π × radius² × height (enter the diameter and the calculator halves it). Add one row per element — a patio plus its footings, say — and the total covers the whole pour.
Frequently asked questions
How much concrete do I need for a slab?
Multiply length × width × thickness (in feet) and divide by 27 for cubic yards. A 10×10 slab at 4 inches is about 1.23 cubic yards. Enter your dimensions above and the calculator gives the volume and bag count, plus a 10% overage.
How many 80 lb bags of concrete are in a cubic yard?
About 45. An 80 lb bag yields roughly 0.60 ft³ and a cubic yard is 27 ft³, so 27 ÷ 0.60 ≈ 45 bags. It's about 60 bags of 60 lb or 90 bags of 40 lb.
How much does a yard of concrete cost?
Ready-mix is typically around $125–$160 per cubic yard delivered (2026), before short-load or pump fees. Bagged mix costs more per yard but suits small jobs. Enter a price per bag above to estimate the bagged cost.
How much concrete for a 40x60 slab?
A 40 ft × 60 ft slab at 4 inches is 40 × 60 × 0.333 ÷ 27 ≈ 29.6 cubic yards — order around 33 with a 10% overage. At 6 inches it's about 44.4 cubic yards. Use the calculator for your exact thickness.
What is the 1-2-3 rule for concrete?
It's a basic mix ratio by volume — 1 part cement, 2 parts sand, 3 parts gravel (stone), plus water — that produces a general-purpose concrete around 3,000 psi. Bagged pre-mix already contains the right proportions.
Should I add extra concrete to my order?
Yes — about 10% extra to allow for uneven subgrade, spillage and form movement. The calculator adds your chosen waste percentage so you don't run short mid-pour.
Researched & verified by the Calcuris Data & Research Team. How we build and check our tools →