How to use the Concrete Calculator tool
3 simple steps · under a minute
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Choose the shape
Pick a slab (patio, driveway, footing) or a round column or post hole.
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Enter the size
Type length, width and thickness, or diameter and depth, and how many you need.
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See how much to buy
Read cubic yards for a ready-mix order, or the number of 80, 60 or 40 lb bags.
About Concrete calculator
Ordering too little concrete is costly and too much is wasteful. This concrete calculator works out the volume for a slab, patio, sidewalk or footing — length × width × thickness — or for a round column or post hole, and converts it to cubic yards and pre-mixed bags.
A standard 4-inch patio slab of 10 × 10 feet needs about 1.23 cubic yards of concrete, or around 56 bags of 80 lb mix before waste. For jobs over about one cubic yard, ready-mix delivery is usually cheaper and easier than mixing bags by hand.
Yards or bags
Cubic yards for a ready-mix truck, or bag counts for small jobs.
Slabs and columns
Patios, sidewalks, footings, fence posts and sonotubes.
Waste allowance
Adds extra for spillage and uneven ground, 5–10% being typical.
Frequently asked questions
How do I calculate concrete in cubic yards?
Multiply length (ft) × width (ft) × thickness (ft), then divide by 27. Convert thickness in inches to feet by dividing by 12.
How many bags of concrete make a yard?
About 45 bags of 80 lb mix or 60 bags of 60 lb mix make one cubic yard.
How thick should a concrete slab be?
4 inches is standard for patios and sidewalks; 5–6 inches for driveways and heavier loads.
How much extra concrete should I order?
5–10% extra covers spillage, over-excavation and uneven ground.
How much concrete for a fence post?
For a 10-inch hole 3 feet deep, about 1.6 cubic feet per post — roughly three 60 lb bags.