How Many Cubic Feet Are in a Bag of Concrete?

How Many Cubic Feet Are in a Bag of Concrete?

An 80 lb bag of concrete yields about 0.60 cubic feet, a 60 lb bag yields about 0.45 cubic feet, and a 40 lb bag yields about 0.30 cubic feet. Those numbers are for standard mixed concrete once you add water, and they are the figures you use to work out how many bags a job needs.

I have poured a lot of small slabs, footings, and post bases off bagged mix, and the single most common mistake I see is buying by weight instead of by volume. Weight tells you how heavy the bag is. Yield tells you how much finished concrete you actually get. Those are two different things, and the yield is the number that matters when you are standing in the aisle deciding how many bags to load.

Cubic feet per bag by size

Here are the yields I plan around. Manufacturers print these on the bag, and they vary a hair between brands, but these are safe working figures.

Bag size	Cubic feet per bag	Bags per cubic yard	Approx. weight
40 lb	0.30 cu ft	90	40 lb
50 lb	0.375 cu ft	72	50 lb
60 lb	0.45 cu ft	60	60 lb
80 lb	0.60 cu ft	45	80 lb

A cubic yard is 27 cubic feet, so to get bags per yard you just divide 27 by the yield. That is where the “45 bags in a yard” figure for 80 lb bags comes from. If you want that broken down further, I wrote it up in how many bags in a yard.

How to figure bag coverage for your job

The method never changes. Get the volume of what you are pouring in cubic feet, then divide by the yield of the bag you plan to buy.

Multiply length by width by thickness, with every measurement in feet, to get cubic feet:

cubic feet = length_ft x width_ft x thickness_ft

If your thickness is in inches, divide it by 12 first. Say you are pouring a 4 ft by 4 ft equipment pad, 4 inches thick:

• 4 in divided by 12 = 0.33 ft
• 4 x 4 x 0.33 = 5.28 cubic feet
• 5.28 divided by 0.60 (an 80 lb bag) = about 9 bags
• 5.28 divided by 0.45 (a 60 lb bag) = about 12 bags

Same slab, different bag size, very different bag count. That is the whole reason yield matters more than weight.

Bag size versus ready-mix

There is a break-even point. Bagged concrete is convenient for small work and jobs you can mix as you go, but the cost and labor climb fast. Once a project pushes past roughly 1 cubic yard, or about 45 to 60 bags, you are usually better off ordering ready-mix by the truck. Mixing 50-plus bags by hand is a long, wet, back-breaking day, and the bag price adds up to more than a short-load delivery in a lot of markets. If you are on the fence, run the volume both ways and compare. Our guide on how much concrete do I need walks through that decision.

Always add for waste

Add 5 to 10 percent on top of your calculated volume. Bags spill, subgrade is never perfectly level, and you will lose a little mix to the mixer and your tools. Running one bag short in the middle of a pour means a cold joint or a trip to the store while your concrete sets. Buying one extra bag costs a few dollars. That trade is not close.

Let the calculator do it

Rather than run these numbers by hand, drop your dimensions into the concrete bag calculator and it returns the exact bag count for 40, 60, and 80 lb sizes, waste factor included. For anything sized in cubic yards, the concrete yardage calculator converts your slab or footing straight to yards so you can compare bags against a ready-mix order.

FAQ

How many cubic feet are in an 80 lb bag of concrete?

About 0.60 cubic feet of mixed concrete per 80 lb bag. That means it takes roughly 45 bags to fill one cubic yard.

What is the yield of a 60 lb bag of concrete?

A 60 lb bag yields about 0.45 cubic feet. You need about 60 of them to make a cubic yard, which is why 60 lb bags suit smaller pours where you want lighter bags to carry.

How many 80 lb bags do I need for a cubic yard?

Around 45 bags. Divide 27 cubic feet by the 0.60 cubic foot yield of an 80 lb bag. Add a couple extra for waste and spillage.

Is it cheaper to use bags or ready-mix?

For jobs under about a cubic yard, bags usually win on total cost and convenience. Above that, ready-mix delivery is typically cheaper once you count the bag price and the labor to mix them.

Why does bag weight not equal coverage?

Weight is how heavy the dry bag is; yield is how much finished concrete you get after adding water. Two bags can weigh the same but a wetter or denser mix changes the finished volume, so always plan off the printed cubic feet figure.

How much waste should I add for bagged concrete?

Add 5 to 10 percent. Spillage, uneven subgrade, and leftover mix in the mixer all eat into your count, and running short mid-pour is far more expensive than one spare bag.

Ready to buy the right number the first time? Run your dimensions through the concrete bag calculator and get an exact bag count in seconds.