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Concrete Calculator
Estimate concrete in cubic yards, cubic feet and bags for slabs and columns.
Concrete Calculator
Imperial units (feet & inches). Order 5–10% extra for spillage and uneven ground.
How much concrete do I need?
Concrete is ordered by volume. For a rectangular slab, multiply length × width × thickness. For a round column, use π × radius² × height. This calculator converts everything to cubic yards and tells you how many bags you'll need.
Handy rules of thumb
- One cubic yard = 27 cubic feet = about 0.765 cubic metres.
- An 80 lb bag yields about 0.6 cubic feet; a 60 lb bag about 0.45 cubic feet.
- A 4-inch slab covers about 81 square feet per cubic yard.
Always round up and add a little extra — running short mid-pour is costly.
Frequently asked questions
How many bags of concrete make a cubic yard?
It takes about 45 bags of 80 lb concrete or about 60 bags of 60 lb concrete to make one cubic yard.
How thick should a concrete slab be?
A standard driveway or patio slab is 4 inches thick; areas carrying heavy loads like a garage floor are usually 5–6 inches.
How do I calculate concrete for a column?
Use volume = π × radius² × height. Enter the diameter and height in this tool and it computes the volume and bag count for you.
Should I add extra for waste?
Yes — order about 5–10% more than the exact volume to allow for spillage, uneven subgrade and slight over-digging.