flat bag volume

How can I determine the volume a bag will hold given its flat dimensions? Say a sandbag 20 x 36"? Is there a formula to estimate volumes of flat bags?

[Robert Fogt]

You would need 3 dimensions to calculate volume.

volume = length * width * height

If each dimension is in inches, the volume will be in cubic inches.

[Robert Fogt]

This seems to be a good time to mention a new calculator I added to the site. It calculates the volume of a rectangular object.

http://www.onlineconversion.com/object_volume_box.htm

[QUOTE=Robert Fogt]what is the formula for calculating polythene bag volume and the conversion of area to volume

[Robert Fogt]

The conversion for area to volume is:
volume = area * height

To calculate the volume of a bag you need:
volume = length * width * height

With all due respect, Robert Fogt does not seem to have the imagination needed to generate a formula to find the volume of a flat bag. Perhaps he never put a sandwich in a baggie. We know you need 3 dimensions to generate a volume. But flat bags are defined by 2 dimensions only. Nonetheless, they get filled all the time. If it was easy, I’d do it myself, but the math gets pretty complex. Let’s start by defining terms. Bags are usually given as Length (L) by Width (W), with the opening on the W side. That makes the circumference (C) of the opening 2W. The diameter of that opening, 2W/Pi, would be the maximum depth of our flat bag. We could use L x 2W/Pi, but both ends are flat. I suspect the formula would be something like (L/W x constant (K)) x 2W/Pi x L. We could, I suppose, fill up a bunch of various sizes of bags and see if a pattern emerges, but a mathematical formula seems much cleaner, don’t you think? Any thoughts? Anyone?

How about this: for the case where the length of the bag is longer than the width, so the center can go to a cylinder I'm postulating this formula:
V = ((Wsquared/Pi) x (L-W)) + (1/2 or 1/4 or 1/8 x Wcubed/Pi).

[gubment_cheez]

Originally Posted by drcruzr

How about this: for the case where the length of the bag is longer than the width, so the center can go to a cylinder I'm postulating this formula:
V = ((Wsquared/Pi) x (L-W)) + (1/2 or 1/4 or 1/8 x Wcubed/Pi).

so lets review.
((W²/pi)*(L-W))+([.5|.25|.125]*W³/pi) = V
and lets take a bag that is 20W x 20L those are nice even measurements
((20²/pi)*(20-20))+([.5|.25|.125]*20³/pi)
(127.32395447351626861510701069801 * 0) + (.5|.25|.125]*20³/pi)
0 + 1273.2395447351626861510701069801
oooor
0 + 636.61977236758134307553505349006
oooor
0 + 318.30988618379067153776752674503

interesting

What if you wanted to know the volume at any time not just the maximum volume?

I hate being wrong, but have to admit it when I am. My first shot at a formula to estimate the volume of a flat bag seriously UNDERestimated the actual values I was able to obtain experimentally. I still think it should be close for very long bags, but for bags where the length and width are at all close, it's not too good. I'm still open to suggestions. Does anyone know people who work with flat bags? They must know something we don't...