# How to Calculate Store Bought Concrete Coverage by Bag Size



## jogr

Thanks Willie! How much water is typically used per 80 lb bag of concrete? Any tips on the best way to mix up a bag or two at a time?


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## Willie T

jogr said:


> Thanks Willie! How much water is typically used per 80 lb bag of concrete? Any tips on the best way to mix up a bag or two at a time?


1.36732 gallons per bag. *Just kidding! *(Although that is probably pretty durn close.)

You simply add water, progressively, till the concrete is about the consistency of cake icing. Don't go too far. You don't want it soupy... that weakens the concrete and encourages cracks.

The best mixing setup I've found (short of renting a motorized mixer) is to use a strong 1/2" drill (no smaller!!!) with a paddle the stores sell for mixing like this... about $15.

Screw (from the inside) the bottom of a 5 gallon plastic bucket to the center of a 2'x2' piece of plywood (3/4" is best). Stand on the left and right edges of the plywood with the bucket kind of between your legs, and mix slowly.

Start with about a third of the bucket full of dry concrete mix and enough water to keep it a little sloppy. This keeps from overworking the drill. Feed more concrete and water as it all gets mixed well.

Keep going, balancing the concrete-to-water ratio, till you have a fairly full bucket that is soft like cake icing. Keep lifting the mixer paddles up and down to be sure to get all the concrete mixed in well.

Run your paddles around the deep rim of the bucket a lot. Dry concrete likes to pocket down there. Get it out of there with the motion of the paddles, and get it mixed in.


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## Mort

jogr said:


> Thanks Willie! How much water is typically used per 80 lb bag of concrete? Any tips on the best way to mix up a bag or two at a time?


They recommend starting with a gallon, and add a little more until it is workable. I've found that a gallon gets you to about a 1" slump, which is pretty much unworkable in most situations. Another quart makes it about a 4" slump, which is good most of the time.


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## 1forest1

Alot of great formula reminders here Willie. 

I'll just add another trick that most of us might find easier to remember than the 0.083 inch-to-foot ratio.

12 inches in a foot. So 4 inches is *4/12*'s of a foot.... There's your formula! 4 divided by 12 = .333 of a foot

Much easier to figure out, while standing beside the wheelbarrow 

I much prefer using decimals. We are supposed to use metric up here in Canada, but in reality, it becomes an ugly mish-mosh of both. Dimensions will be scribbled in ft/inch (from a tape measure), but the products are supplied in Kg or Liters. Sigh...


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## Willie T

1forest1 said:


> Alot of great formula reminders here Willie.
> 
> I'll just add another trick that most of us might find easier to remember than the 0.083 inch-to-foot ratio.
> 
> 12 inches in a foot. So 4 inches is *4/12*'s of a foot.... There's your formula! _4 divided by 12 = .333 of a foot_
> 
> Much easier to figure out, while standing beside the wheelbarrow
> I much prefer using decimals. We are supposed to use metric up here in Canada, but in reality, it becomes an ugly mish-mosh of both. Dimensions will be scribbled in ft/inch (from a tape measure), but the products are supplied in Kg or Liters. Sigh...


Yes, that was covered in my third paragraph. I gave the .083 so that anyone could use it to simply *multiply* any number of inches for an answer. (easier to do standing by the wheelbarrow, than a *division* problem)


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## 1forest1

Willie T said:


> Yes, that was covered in my third paragraph. I gave the .083 so that anyone could use it to simply *multiply* any number of inches for an answer. (easier to do standing by the wheelbarrow, than a *division* problem)


I politely disagree. Its easier to take the two numbers and divide them on the spot (beside the wheelbarrow), than commit to memory a 3-digit decimal number that gets you to the same place.... Why is it easier to multiply 6x0.083 than to divide 6"/12"? They both get you 0.5.


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## Willie T

1forest1 said:


> I politely disagree. Its easier to take the two numbers and divide them on the spot (beside the wheelbarrow), than commit to memory a 3-digit decimal number that gets you to the same place.... Why is it easier to multiply 6x0.083 than to divide 6"/12"? They both get you 0.5.


 If you find division easier than multiplication, go for it.

Now everyone reading this has a choice.


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## danrb007

With all the smart phones out there now there a few good apps for doing the conversions and multiplying all on the phone. Some are free and others cost just a little bit but well worth the price.


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## mwpiper

I use the wheelbarrow and hoe method. This allows mixing whole bags and when I'm done mixing it's al ready to transport and pour. I have a calibrated bucket so all I need to do is dump bag, pour water, stir, dump, repeat. The bucket has an old patch mortar stuck to the side that looks like England. I fill it to Liverpool.


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