# How many bags of concrete do I need?

I would like to make a small concrete slab of the following dimensions.

``````Length: 1.2m
Width: 0.86m
Depth: 0.09m
``````

The cubic volume as i understand it is all those numbers multiplied.
result: 0.0929m2

If a bag of pre-mix concrete says
0.2m2 x 50mm

How many bags would I need?

Update: Brick BBQ construction. I am doing this for "homework" :)

• Your volume should be in cubic meters. Trivial, but true. Commented Nov 30, 2012 at 0:03

I would say 10 or 11 bags (depending on how sloppy you are).

``````0.2 * .05 = .01

.0929 / .01 = 9.29 bags
``````

Since you never get perfect yield from a bag, I would personally go with 11 bags.

• It might be that it actually says a square .2 meters on a side. This seems a more likely way of specifying the useful volume of the bag. Just in case that makes your numbers off by 1/2. The number in that case would be 19 or 20 bags. Commented Nov 30, 2012 at 0:12
• Looking again, this looks like a homework problem, so it doesn't have to reflect common sense at all. Commented Nov 30, 2012 at 0:18
• "Homework"? I guess it is. See my in progress home work LOL. Have updated my post. The calculation was quite accurate. After resizing the slab, we calculated 12 bags. I bought 14 and returned 1 back to the shop. Commented Nov 30, 2012 at 2:03
• Nice work, Valamas. Commented Nov 30, 2012 at 8:52
• Glad it worked out for you! Very nice fire place too! Commented Nov 30, 2012 at 13:36