Concrete Calculator
Cubic yards and bags for slabs, footings, and round columns.
Your estimate
Estimates only. Renovate Cafe's calculators are a planning aid, not professional advice — double-check your inputs, confirm coverage on the product you buy, and verify quantities and local code for structural, electrical, or permitted work. Disclaimer.
Pick your shape, enter the dimensions, and Renovate Cafe returns the volume in cubic yards, how many bags of each size that is, and the cost of bagging it versus ordering ready-mix.
Slabs, footings, and columns
Concrete is volume work. For a slab, footing, or wall, multiply length × width × thickness (with thickness converted from inches to feet) to get cubic feet, then divide by 27 for cubic yards. For a round column or tube form, the area of the circle (π × radius²) times the height gives the volume of one, multiplied by how many you're pouring.
A 60 lb bag yields about 0.45 cubic feet of mixed concrete; an 80 lb bag about 0.60. The calculator divides your total volume by the bag yield and rounds up. It also adds a small overage, because nobody wants to be short halfway through a pour.
Bags or ready-mix?
The rule of thumb: under about ½ cubic yard, bags win on convenience and price. Past 1 cubic yard, the math — and your back — favor ordering ready-mix from a truck. A cubic yard is forty-five 80-lb bags; mixing that by hand is a long, hard day. The calculator shows the bag count and the ready-mix cost together so you can decide.
Thickness matters: 4 inches is standard for patios, walkways, and shed pads; 5–6 inches for driveways and anything that carries vehicles. Always pour over a compacted gravel base, and order 5–10% extra for ready-mix to cover uneven subgrade.
Frequently asked questions
How many 80 lb bags of concrete in a yard?
How thick should a concrete slab be?
Is it cheaper to mix my own concrete or order ready-mix?
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