How many 80lb bags of Quickrete will it take for a 20’ x 12’ x4” slab?

  • Are you completing this yourself? Mix, pour, and finish? DIY? Is this for a cost comparison? If you could add some more details it will make it a more interesting read and thus a better question. Please also take the tour
    – P2000
    Mar 31, 2022 at 18:01
  • 2
    Unless you're off the grid (by which I mean the ready-mix network), you don't want to do this from bags.
    – isherwood
    Mar 31, 2022 at 18:18
  • 2
    I’m voting to close this question because it shows a rather distinct lack of effort to research before answering.
    – FreeMan
    Mar 31, 2022 at 21:32

1 Answer 1


Use their calculator!

Enter the area (12x20 is 240 sqft) and the depth of your slab (4in). It will break it down into the required number of bags.

There are some good alternatives to mixing your own bags. See answers under the earlier question Best way to source concrete for a long fence project

For a project this size (I had a similar one) I was wisely advised to get a truck, pump and finishing crew. I have completed smaller sizes alone, with bags and a mixer.

Also note that if you are mixing this yourself, the time spread and mixing variations alone, for a large slab, might give you batch inconsistencies that can become an eyesore. But this is a matter of personal skills & priorities of course.

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  • At least 10 men will be needed to mix and place the concrete. Mar 31, 2022 at 23:25
  • It must all be poured in a few hours to avoid weak boundaries between batches. Mar 31, 2022 at 23:27
  • @blacksmith37 yeah, or OP could form it in manageable sections but then you get separated wet cuts and likely unsightly small sections
    – P2000
    Mar 31, 2022 at 23:44

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