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half pint is 8 fluid ounces.

4 lbs is 64 ounces
8 goes into 64 8 times.

4 lbs is 8 half pints from my calculations

correct me if im wrong

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I know that this is a super old thread to bump, but I just cannot sit by and look at the ridiculous arguments in this thread, and go on leaving it as it is without any definitive statement one way or the other regarding units of volume vs units of mass.

3 x 4lb bags filled with 3 different substrates has got nothing to do with how many 1/2 pint or quart jars could be filled with any of the substrates.

1/2 pint and quart jars are measures of volume in liquid ounces.

Each of the 3 subs will have a different density (mass to volume ratio).  Therefore each of the subs will fill a different number of jars (of any size) when divided.

Since the subs are made up of fibers and other things which are not liquid, not to mention things like air gaps between grains of different sizes, etc., they cannot be volumetrically measured with any accuracy without first knowing the specific density of each substrate.

To find this out you would need to first fill a known volume (let's say a pint aka 16 fluid ounces) and then weigh it to find the mass (remembering to subtract the mass of the container itself), then divide by the total number of units of measure in volume to get the density in (example) grams per fluid ounce.

So, for water, 16 fl oz will completely fill a pint.  The mass (not counting the pint container) will be roughly 473.2 grams.  We divide 473.2 by 16 to get the density, which is about 29.6g/fl oz. 

From this density we can find the weight (mass) of any known volume of area simply by multiplying the volume in fl oz by 29.6 to find the mass in grams.

Alternately we can find the volume of a known weight by dividing that weight by 29.6 to find the volume in fl oz.

It should be obvious that since substrates are not pure liquids, and will have some air between the particles if nothing else, then most likely a pint of substrate is not equal to 473.2g.  Probably it will weigh substantially less than this due to a variety of factors.

So, to try and figure out a number of smaller volumes which is equivalent to any of the the substrates based solely upon its weight is impossible.  It's even more impossible to assume that the densities of three completely different kinds and shapes of substrates will fill an equal volume of smaller volumes equally.

Again sorry for the bump, but I hope that everyone reads and understands this. 

This is very basic science. 

Fluid ounces are a measure of volume only.  For water it is also a measure of mass (weight).  Unless whatever is being measured has the exact same density as water then 1fl oz (volume) does not equal 1oz (mass, as in 1/16th pound).

The same applies to liters or ml.  It is a unit of volume.  For water 1 ml = 1 gram.  For anything which is not water 1ml does not = 1 gram (unless the item being measured has the exact same density as water).

Of course atmospheric pressure can have a large impact on some materials, but that is a whole different argument and I think it's pretty safe to say that people are generally on the earth in about 1 standard unit of atmospheric pressure when measuring substrates.

Not two miles under the sea, and not on the space station.  You are reading this on the earth, damnit!  LOL!