Bagged Concrete vs Ready-Mix: Which Do You Need?

None of the sources checked for this guide gives a line where bagged concrete stops and a ready-mix truck starts. What can be worked out is what each route asks of you: one cubic yard is about 45 bags of 80 lb mix, roughly 3,600 lb, by this site’s arithmetic on QUIKRETE’s yield figure. A ready-mix order asks for different things: a list of details for the supplier and a way to get a heavy truck to the pour.

How many bags make a cubic yard

QUIKRETE’s data sheet for its Concrete Mix lists a yield for each bag size, including approximately 0.30 cu ft for a 40 lb bag, 0.45 cu ft for a 60 lb bag, and 0.60 cu ft for an 80 lb bag.

A cubic yard is 27 cubic feet. Dividing by those yields gives the bag counts below. The division is this site’s; the yields are QUIKRETE’s.

Bag	Yield per bag	Bags per cubic yard	Weight of those bags
80 lb	About 0.60 cu ft	45	3,600 lb
60 lb	About 0.45 cu ft	60	3,600 lb
40 lb	About 0.30 cu ft	90	3,600 lb

These counts have no extra in them. This site’s Concrete Calculator adds 10% by default.

What a cubic yard of bags takes: weight and mixing

Whichever bag size you buy, a cubic yard is about 3,600 lb of dry mix to load, unload, and lift into a mixer.

Then there is the water. QUIKRETE’s machine-mixing instructions say each 80 lb bag will require about 3 quarts. QUIKRETE’s data sheet puts the final water content at approximately 6 to 9 pints per 80 lb bag, which is 3 to 4.5 quarts. At 3 quarts a bag, 45 bags take about 135 quarts, a little under 34 gallons, measured out bag by bag.

The measuring matters. The same instructions say that the more water is added to the mix the weaker it becomes, and that adding one extra quart of water per 80 lb bag can reduce the strength of the concrete by up to 40%.

QUIKRETE says its concrete mixes can be mixed by hand or by machine, and that for larger projects machine mixing is often the best method. Its shopping list for machine mixing names a 3 cubic foot barrel mixer. The data sheet says to allow at least 1 cubic foot of mixer capacity for each 80 lb bag mixed at one time. At that rate a 3 cubic foot mixer takes at most three bags at a time, and 45 bags is at least 15 batches.

What to tell a ready-mix supplier

The National Ready Mixed Concrete Association (NRMCA) says the customer for ready mixed concrete is typically a concrete contractor. It says the producer keeps several mixture formulations for different applications and can help with selecting the right one.

The guide lists what to include when ordering:

• Strength. NRMCA says a specified strength of 3,500 to 5,000 psi is typical for most concrete applications.
• Slump, which is how stiff or loose the concrete is when delivered. For most applications the slump required is 3 to 5 inches.
• Air content. NRMCA says air-entrained concrete is required for concrete exposed to freezing temperatures in service.
• Quantity. Concrete is sold by volume, in cubic yards, and NRMCA says to order 4% to 10% more than an estimate calculated from the plan dimensions.
• Delivery. NRMCA says to give the producer the street address, the location and nature of the placement, and the estimated delivery time and placement duration, and to say how the concrete will be placed.

NRMCA also says concrete is a perishable product and the crew should be ready for placement when the truck arrives.

The guide does not give a minimum order or a price for a small load. Ask the supplier about both when you call.

Can the truck get to the pour

NRMCA says the capacity of truck mixers varies between 8 and 12 cubic yards, and that a loaded concrete truck weighs about 80,000 lb. It says a loaded truck may not be able to maneuver on loose dirt or over residential curbs and pathways, and to consider alternative conveying and placing methods when access is limited.

So before you order, walk the route from the street to the forms and tell the supplier what is in the way.

A checklist for deciding

None of the sources gives a volume at which to switch, and this page does not either. This site’s Concrete Calculator shows a note to compare a ready-mix quote when a result is over 1 cubic yard. That is this site’s own rule of thumb, chosen because a cubic yard is about 45 bags of 80 lb mix, not a published standard.

Questions the figures above let you answer for your own job:

• How many bags is it, and what do they weigh in total?
• Do you have a mixer, and people to keep it fed, for that many bags?
• Can you measure the water for every bag?
• Can a loaded truck reach the pour, or will the concrete have to be moved from the street?
• Will the forms and the people be ready when the truck arrives?
• What does the supplier charge for the amount you need, and is there a minimum?