How many 60lb bags of pre-mixed concrete will I need to make a 4 foot by 4 foot sidewalk square at 4 inches thick? (16 sq.feet) I only found one web based calculator and it said I need almost 40 bags. That cant be right. Heck, the bags are close to 4 inches thick and they are larger than a square foot. Math is not my thing....
This one says 12 bags;
I used about 43 bags of the 80 lb size for a hole 3x3 feet and about 3 feet deep.
Buy 15 to be safe.
No, it's not. An 80# bag will make about 2/3 cubic foot of concrete when mixed. You need 4' x 4' x 1/3' = 5-1/3 cu ft; divide that by 2/3, and you get eight **80** pound bags, or eleven 60-pound bags. I'd get one more, to be on the safe side.
Measure one, and you'll find it's a lot closer to 2-1/2".
And it takes up *less* space after you mix in the water.
That 155 pounds per cubic foot includes the water, thus leading you to overestimate the amount of dry mix needed. I put it at 11 bags.
steve
60lb=1/2cu ft
I get the same number. Maybe the OP calculated based on 16 CUBIC feet instead of 16 SQUARE feet at 4" thick. The math seems about right.
JK
I have found it is faster to do these calculations in cubic inches if you have one of those new fangled calculator things.
No way. A cubic foot of concrete weighs between 140 and 155 pounds.
I think they're saying that a 60 pound bag makes 1/2 CF of concrete. The bound water makes up the difference in weight.
R
Like I pointed out to you before... you're forgetting about the water.
I think "they" will not have enough concrete to fill the forms. I hate making bagged concrete pours, but occasionally they are a necessary evil in the business. I make an accurate take off on required volume and figure 80 pound bags at 1/2 CF. 40 and 60 pound bags are easier to carry and make the cost per bag look good, but weight is weight. 60 plus 60 just won't make 150.
call a local concrete guy, they may have a larger job in the area, bag concrete costs a fortune.
a add on job may be cheaper than buying and mixing bags
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.