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. In metric, a 30 kg bag makes roughly 0.014 m³, so a cubic metre takes about 1 ÷ 0.014 ≈ 71 bags.

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.

Why does the tool say 1.36 yards but tell me to order 1.5?

Because a ready-mix plant batches to a step — commonly the half yard — and you cannot order 1.36 of anything. The first number is the arithmetic; the order line rounds it up to the step the truck can actually deliver. Bags work the same way: 61.1 bags means you buy 62, because the sixty-second bag is not sold in tenths.

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 (about 100 mm); 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 — or use the footing calculator , which is the same arithmetic with footing-shaped defaults. A round pier (a sonotube) is a cylinder rather than a box: the concrete column calculator does those from the diameter.

Ready-mix or bags — where is the break-even?

It depends on two prices you know and this page does not: what the plant charges per yard delivered (including any short-load fee) and what a bag costs you. Type both into the comparer below the worked example and it tells you the volume where the truck becomes cheaper. For most people it lands well under a yard once the short-load fee is counted.

Calculateur de béton

Voir le calcul — avec vos chiffres

Before you type — how to measurefor a slab

Measure inside the forms, form face to form face. The outside of the forms is bigger by two board thicknesses, and that is not where the concrete goes.
Thickness is from the top of the compacted base to the finished surface — not from the bottom of the excavation. If the base is uneven, measure it in three or four places and use the deepest.
A thickened edge or a haunch is a second pour: run it through the tool as its own length × width × depth and add the two.
Write the units on the tape reading. "10" is not a number; "10 ft" is. The tool wants feet for length and width and inches for thickness — a 4 typed into the length box is a four-foot slab. Set to metric it wants metres for length and width and centimetres for thickness: 10 cm, not 100.

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. Open Show the working under the form and the arithmetic is written out with your own numbers in it — the same lines you would put on the back of a delivery slip.

Same pour, different shape

The arithmetic changes with the shape, so each shape has its own page.

Exemple détaillé

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 at 1.36 yd³, which the plant rounds up to 1.5 yd³ — the half-yard step a truck batches by. Bagging it instead, at 0.6 ft³ per 80 lb bag, would take 36.7 ÷ 0.6 ≈ 61 bags with waste — which is exactly the point where a truck starts to look attractive.

The same pad in metric: 3 m × 3 m at 10 cm is 3 × 3 × 0.10 = 0.9 m³. With 10% waste that is 0.99 m³, which the order line rounds up to 1.0 m³. In 30 kg bags at about 0.014 m³ each it is 0.99 ÷ 0.014 ≈ 71 bags.

Ready-mix or bags?

Two prices decide it, and both are yours to type: the plant's delivered price per yard — or per cubic metre, with the site set to metric — (fold any short-load fee into it) and what a bag costs you. The comparer works out the pour size at which the truck becomes cheaper.

Béton prêt à l’emploi livré, par yd³

$/yd³

Incluez le supplément pour petite charge, réparti sur vos verges cubes.

Un sac de 80 lb (0,6 ft³)

$/sac

Changez le rendement ci-dessous si votre sac est différent.

Rendement par sac

ft³

Ce qu’un sac donne réellement — lisez-le sur le sac, les marques diffèrent.

Tapez les deux prix pour comparer.

Garder ces résultats

Nous envoyons ce seul courriel par notre fournisseur de courriel et ne gardons pas votre adresse.

What went wrong?

Three ways a concrete takeoff goes wrong, and they are the same three every time. Each problem below is one of them — find which.

Quick referencefor a pour

A cubic yard: 27 ft³ — 3 ft × 3 ft × 3 ft · about 45 bags at 0.6 ft³
Thickness as feet: 4 in = 0,333 · 5 in = 0,417 · 6 in = 0,5 · 8 in = 0,667 · 12 in = 1
Yards from an area: at 4 in: ft² ÷ 81 · at 6 in: ft² ÷ 54 · at 8 in: ft² ÷ 40.5
Order: yards × 1.10, rounded UP to the half yard
A 10 yd³ truck: roughly a 30 × 27 ft slab at 4 in, or 135 ft of 24 × 12 in footing
Métrique: 1 m³ = 1.31 yd³ · 100 mm ≈ 4 in · a 30 kg bag ≈ 0.014 m³
Metric pour: m² × thickness in m — 9 m² at 100 mm = 0.9 m³ · about 71 bags of 30 kg to the m³

Waste & overagewhat to add, and why

Ready-mix orders carry 5–10% over the takeoff — the sub-base is never perfectly flat, forms bow, and a truck that arrives half a yard short costs a second delivery fee and a cold joint. That margin is the waste field.
Plants batch to the half yard (some to the quarter); the order line already rounds up, so do not round again on top of it.
A short-load fee applies under a set number of yards; if you are a hair under it, ask what the minimum is — sometimes it is cheaper to take the full minimum than to pay the fee on less.

Mistakes to catchbefore you order

Measuring the outside of the forms — the concrete goes inside them. Two 2×4 form boards add 3 in to a dimension, which on a small pad is a few percent of concrete you pay for and never place.
Typing a thickness in inches into a metric-set tool, or vice versa — a slab set at 10 cm is 4 in, not 10 in.
Forgetting the thickened edge or the haunch; it is a second rectangle and belongs in its own calculation added to the slab.

What an inspector looks forthe building inspector, at the pre-pour call

On this part of the job

That the hole or form matches the approved drawing — length, width and depth measured off the same datum the plan uses, not off the pile of spoil beside it.
Bearing: undisturbed soil or compacted base under the whole pour, no soft spot, no water, no loose crumbs in the bottom of the form.
Steel in place and supported before the truck arrives — the right bar, the right spacing, on chairs, tied, and lapped where lengths meet. Bar lying on the ground fails.
Forms braced and to line. A form that bows takes more concrete than you ordered and leaves a wall you cannot straighten afterwards.
The mix on the delivery ticket matching what was specified — strength, aggregate size and any air entrainment are written on the ticket, and the ticket is the record.

Have this ready

The stamped drawing or permit set, open to the foundation plan.
A tape and a level so the inspector can check a dimension without going back to the truck.
The ready-mix ticket for every load, kept together — an inspector who cannot see the tickets cannot sign the pour.
Your own takeoff, so a short load is a phone call and not a cold joint.

Every figure an inspector measures against comes from the code your jurisdiction has adopted, the stamped drawing, or the manufacturer's printed instructions — so none of them are printed here. Look the number up in your own book, type it into the tool, and the arithmetic is yours.

La formule

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. Switching between imperial and metric converts the dimensions you typed rather than resetting them, and says so under the depth field.

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. In metric, a 30 kg bag makes roughly 0.014 m³, so a cubic metre takes about 1 ÷ 0.014 ≈ 71 bags.
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.
Why does the tool say 1.36 yards but tell me to order 1.5?: Because a ready-mix plant batches to a step — commonly the half yard — and you cannot order 1.36 of anything. The first number is the arithmetic; the order line rounds it up to the step the truck can actually deliver. Bags work the same way: 61.1 bags means you buy 62, because the sixty-second bag is not sold in tenths.
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 (about 100 mm); 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 — or use the footing calculator, which is the same arithmetic with footing-shaped defaults. A round pier (a sonotube) is a cylinder rather than a box: the concrete column calculator does those from the diameter.
Ready-mix or bags — where is the break-even?: It depends on two prices you know and this page does not: what the plant charges per yard delivered (including any short-load fee) and what a bag costs you. Type both into the comparer below the worked example and it tells you the volume where the truck becomes cheaper. For most people it lands well under a yard once the short-load fee is counted.

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