cubic dimensions of a sandbag

Factual Questions
1

If a sand or earth bag is described as 18 by 24 inches, how do you express or figure the third dimension of it? Since the bags are not neat and straight when filled but rather “rounded”, what is the likely h x w x l once the bags is filled with dirt and pounded into a brick-like shape? Is there a general equation for the volume made when two flat rectangular items are sewn or sealed together on three ends to make an envelope or sack? Or do you need additional information? Seems like I should know this, but … I don’t. :smack:

Specifically, if it matters, I’m thinking of bags like this which grains often come in:
http://www.donalddavisbags.com/poly-p.html

Bonus question: How do you type that into WolframAlpha (my new favorite toy)?

2

Yeah, you’d need additional info. Looking at the pictures, it looks like the filled bag has height half the width. The circumference won’t change, so h+w = w(flat) = 18, or h = 6 and w = 12. The final length would be L(flat) - 6 = 18, so you’d end up with a 6 by 12 by 18 inch brick. I suppose it’s also possible that the 18 by 24 quoted dimensions are filled dimensions.

Best bet unless someone with experience shows up here would be to call or email for more info.

3

I think this is the paper bag problem.
Formula at link.

4

My calculation gives a volume of 61218 = 1296. Using the formula from that page, the volume would be 1686 cubic inches. A rectangular volume isn’t as efficient as the shape that formula assumes, so that’s to be expected.

5

If you are purchasing bags for the purpose of using them as sand bags, won’t the manufacturer tell you how much they will hold?

6

Good point. I guess I’m not buying so didn’t want to bother them, and I wondered if there was a generic formula.