How many 80 lb bags of concrete are in a cubic yard?

About 45. An 80 lb bag of pre-mix makes roughly 0.6 cubic feet once mixed, and a cubic yard is 27 cubic feet, so 27 ÷ 0.6 ≈ 45 bags. A 60 lb bag is about 0.45 cubic feet, so it takes closer to 60 of those. Bagging a full yard is a lot of mixing — past about ten bags, ready-mix is usually cheaper and faster.

Should I order extra concrete?

Yes. Sub-grade is never perfectly flat, forms bow, and you cannot go back for "a bit more" once the truck leaves. The waste field defaults to 10%; on a rough or hand-dug base bump it to 15%. Running short on a pour is far more expensive than a little left over.

What thickness should a slab be?

That is a design decision, not an arithmetic one, so this tool does not assume it — you type the thickness you have been told to pour. A common patio or shed pad is 4 inches; a driveway carrying vehicles is often thicker. Follow your plans or your local authority for anything that has to bear a load.

How do I work out concrete for a footing or a column?

A footing is just a long, narrow slab, so enter its length, width and depth here. A round pier (a sonotube) is a cylinder rather than a box — a dedicated column tool is coming, or use the tank/pipe volume tool in the meantime.

Concrete calculator

This tool multiplies the dimensions you enter. It does not decide how thick a slab should be or whether it will carry a load — that is for your plans, your engineer, or your local building authority. Confirm the pour with your ready-mix supplier before you order.

Enter the length, width and thickness of your pour and you get the volume in cubic yards and cubic metres, plus how many bags it would take. The volume is simply length × width × thickness; the waste factor adds a margin on top so you are not caught short by an uneven base.

Worked example

Say you are pouring a 10 ft × 10 ft shed pad, 4 inches thick. Four inches is 1/3 of a foot, so the volume is 10 × 10 × 0.333 = 33.3 cubic feet. A cubic yard is 27 cubic feet, so that is 33.3 ÷ 27 ≈ 1.23 yd³. Add 10% for waste and you are ordering about 1.5 yd³. Bagging it instead, at 0.6 ft³ per 80 lb bag, would take roughly 55 bags with waste — which is exactly the point where a truck starts to look attractive.

The formula

volume = length × width × thickness

Keep the units consistent: put thickness into feet (divide inches by 12) before multiplying, then divide the cubic feet by 27 to get cubic yards. In metric, depth in centimetres becomes metres (divide by 100), and the answer is already in cubic metres. Bags are the total volume divided by the volume one bag yields.

What this tool assumes

Nothing you cannot change. The thickness, the waste percentage and the yield per bag are all editable fields, because they are the numbers that actually vary from job to job. The one figure baked in is that a cubic yard is 27 cubic feet — that is a definition, not an assumption.

Questions

How many 80 lb bags of concrete are in a cubic yard?: About 45. An 80 lb bag of pre-mix makes roughly 0.6 cubic feet once mixed, and a cubic yard is 27 cubic feet, so 27 ÷ 0.6 ≈ 45 bags. A 60 lb bag is about 0.45 cubic feet, so it takes closer to 60 of those. Bagging a full yard is a lot of mixing — past about ten bags, ready-mix is usually cheaper and faster.
Should I order extra concrete?: Yes. Sub-grade is never perfectly flat, forms bow, and you cannot go back for "a bit more" once the truck leaves. The waste field defaults to 10%; on a rough or hand-dug base bump it to 15%. Running short on a pour is far more expensive than a little left over.
What thickness should a slab be?: That is a design decision, not an arithmetic one, so this tool does not assume it — you type the thickness you have been told to pour. A common patio or shed pad is 4 inches; a driveway carrying vehicles is often thicker. Follow your plans or your local authority for anything that has to bear a load.
How do I work out concrete for a footing or a column?: A footing is just a long, narrow slab, so enter its length, width and depth here. A round pier (a sonotube) is a cylinder rather than a box — a dedicated column tool is coming, or use the tank/pipe volume tool in the meantime.

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