How many bags of concrete are in a cubic yard?

About 45 bags of 80 lb mix or 60 bags of 60 lb mix per cubic yard, since an 80 lb bag yields about 0.6 cubic feet. For anything above roughly 1 cubic yard, ready-mix delivery is usually cheaper and easier than bags.

Should I order extra concrete?

Yes — add 5%–10% for spillage, uneven subgrade, and over-excavation. Running short mid-pour causes cold joints, so it's better to have a little extra than to stop.

Concrete Calculator

Q: How do I calculate concrete for a slab?

Multiply length × width × thickness in feet to get cubic feet, then divide by 27 for cubic yards. A 10 ft × 10 ft slab at 4 inches thick is 10 × 10 × 0.333 = 33.3 cubic feet, or about 1.23 cubic yards.

Work out how much concrete a slab or footing needs — in cubic yards, cubic feet, and bags of pre-mix — with a waste allowance built in.

Concrete needed

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Cubic feet

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80 lb bags

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60 lb bags

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Est. ready-mix cost

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The concrete formula

Cubic feet = Length(ft) × Width(ft) × Thickness(ft)
Cubic yards = cubic feet ÷ 27 · thickness in ft = inches ÷ 12

Worked example

A 10 × 10 ft slab, 4 inches thick: 10 × 10 × 0.333 = 33.3 cu ft ÷ 27 = 1.23 cubic yards (≈ 1.36 with 10% waste). That's about 62 × 80 lb bags — well into ready-mix territory.

Bags vs. ready-mix

Bagged concrete makes sense for small jobs — post holes, small pads, repairs. But it adds up fast: an 80 lb bag yields only ~0.6 cu ft, so a modest slab can need dozens of bags and a lot of mixing. Above roughly one cubic yard, ready-mix delivery is usually cheaper, faster, and gives a stronger, more uniform pour. Always order 5–10% extra — running short mid-pour creates a cold joint you can't undo. For area-only calculations use the square footage calculator, and for garden beds the mulch calculator uses the same cubic-yard math.

Frequently asked questions

How do I calculate concrete for a slab?

L × W × thickness (all in feet) ÷ 27 for cubic yards. A 10×10 ft, 4-inch slab ≈ 1.23 cu yd.

How many bags are in a cubic yard?

~45 × 80 lb or ~60 × 60 lb bags. Above 1 cu yd, ready-mix is usually better.

Should I order extra?

Yes — 5–10% for spillage and uneven subgrade.

Related calculators

Note: Estimates only; subgrade, reinforcement, and mix design affect real quantities. Confirm with your supplier for large pours. Last reviewed: July 2026.