How Many Bags of Concrete Are in a Cubic Yard?

You’re standing in the hardware-store aisle with a stack of concrete bags and a nagging question: how many of these do I actually need, and at what point should I just call the ready-mix truck? Here’s the answer, the math behind it, and where the break-even sits.

The short answer

A cubic yard of concrete is 27 cubic feet. Each bag yields a fixed volume, so you just divide:

Bag size	Yield per bag	Bags per cubic yard
80 lb	0.60 ft³	45 bags
60 lb	0.45 ft³	60 bags
40 lb	0.30 ft³	90 bags

That’s the whole trick: 27 divided by the bag’s yield. The Concrete Bag Calculator does it straight from your slab dimensions so you never have to think in yards at all.

Why bags are rated in cubic feet, not pounds

An 80-lb bag doesn’t make 80 pounds of space — the weight is the dry mix, and once you add water it settles into about 0.60 cubic feet of finished concrete. That’s why two bags of different weights can cost the same per cubic foot but wildly different per bag. Always compare on yield, not weight.

Worked example: a small pad

Say you’re pouring a 6 ft × 6 ft shed pad, 4 inches thick:

• Volume: (6 × 6 × 0.333) ÷ 27 = 0.44 cubic yards, or about 12 cubic feet
• In 80-lb bags: 12 ÷ 0.60 = 20 bags
• In 60-lb bags: 12 ÷ 0.45 = 27 bags

Twenty 80-lb bags is a doable weekend mix with a wheelbarrow or a rented mixer. If the number had come back at 45+, that’s your signal to price a ready-mix delivery instead. The Concrete Slab Calculator is set up for exactly this flat-slab math.

The bags-vs-ready-mix break-even

The honest rule of thumb: under about one cubic yard, bags make sense; over it, order the truck. Mixing 45 bags by hand is roughly 3,600 pounds of material moved twice — into the mixer and into the form — and if you slow down, the first batch starts curing before the last one goes in, creating a weak cold joint. Ready-mix arrives in one continuous, consistent pour.

Delivery has its own catch: many suppliers charge a short-load fee below a full truck (about 10 yards) and have a minimum. So the sweet spot for bags is roughly 0.25 to 1 cubic yard, where you’re past a trivial repair but not yet at truck territory.

Don’t forget to order extra

Whatever the calculator says, buy 5–10% more than the exact number. Forms bulge slightly, subgrade is never perfectly level, and you’ll spill some. Running one bag short mid-pour means a hardware-store run while your first batch sets — the one thing you can’t undo. A leftover bag or two costs a few dollars; a cold joint weakens the whole slab.

Quick reference: common pours

Project	Approx. volume	80-lb bags
Fence post hole (12in dia, 2ft deep)	~1.6 ft³	3 bags
3 × 3 ft landing, 4in	~3 ft³	5 bags
6 × 6 ft shed pad, 4in	~12 ft³	20 bags
10 × 10 ft patio, 4in	~33 ft³	56 bags → get ready-mix

Notice the 10 × 10 patio already blows past the bag threshold. That’s typical — anything patio-sized or bigger is usually a ready-mix job.

Ready to estimate your pour?

Measure your length, width, and thickness, then run the numbers through the Concrete Bag Calculator for a bag count or the Concrete Calculator for cubic yards. Either way, round up, and always verify the final quantity with your supplier before you buy.