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Concrete Bags Calculator

Find how many bags of concrete mix you need in 40, 50, 60, and 80 lb sizes.

Project dimensions
Length
Width
Waste %%

Updates automatically as you change measurements.

Estimated materials
You need approximately
1.23 cubic yards
33.33 ft³ of concrete
With 5% waste: 1.3 cubic yards (recommended when ordering)
40 lb bags
112 bags
50 lb bags
89 bags
60 lb bags
75 bags
80 lb bags
56 bags

Enter your slab or footing dimensions and the tool returns the bag count for each size.

This view breaks the pour into 40, 50, 60, and 80 lb bag counts so you can compare. Remember the tipping point: past about 50 bags, ready-mix delivery is cheaper and avoids cold joints between batches.

Why order extra? The headline number is the exact material your project needs. When you actually order, add about 5–10% on top — the “with 5% waste” figure in the result is a safe starting point. That margin covers what you lose to compaction, cuts around edges and corners, and ordinary spillage during handling. It is cheaper to have a little left over than to stop mid-job and wait on a second delivery.

Field notes

Past about 50 bags, stop bagging and order ready-mix — hand-mixing that volume risks cold joints between batches and eats a whole day. Order 5–10% over; you can't pause a pour to run for more, and a short load means a visible seam. Dampen the subgrade and set your forms dead level first, because concrete finds every low spot and won't forgive a sloppy base.

How the concrete bags calculator works 
cubic yards = (length ft × width ft × thickness ft) ÷ 27
80 lb bags = cubic feet ÷ 0.6

Material density

MaterialDensityPer cubic yard
Cured concrete 150 lb/ft³ 2.02 tons

Sources: Portland Cement Association (concrete density and mix guidance).

Frequently asked questions

How many cubic yards of concrete do I need?

Multiply length × width × thickness in feet and divide by 27. A 10 × 10 ft slab at 4 inches thick needs about 1.23 cubic yards of concrete.

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

It takes about 45 bags of 80 lb concrete mix to make one cubic yard, since each 80 lb bag yields roughly 0.6 cubic feet.

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