Pint is a pound.... one ounce of water by volume = one ounce of water by weight.
Quart, pint is a volume measurement. As long as what you are working with is water it can be measured by volume and as weight at the same time.
However, a pound of feathers will have a different volume than a pound of water. It's close but not the same. Another way to say it... a quart of water doesn't weigh the same as a quart of feathers. Or, a quart of strawberries doesn't weigh the same as a quart of blackberries. The strawberries are denser and will weigh more by volume.
This is the exact problem I face when making tinctures. (volume tinctures). To get around this sticky issue*... I weigh my plant material then add twice that weight of menstrum which = a 1-2 ratio. I'm not concerned with the volume (size of the jar).
What exactly are you trying to measure? It might be easier to figure out if I knew the goal/purpose of your measuring.
*sticky issue - fuzzy math for people who don't know math. I do know math so fuzzy math gives me a headache...
the rule i mentioned pretty much applies to everything. i tested it out on various things and some its less and some its more..but all in all its a rule of thumb.
also after canning for years and my rule is a 5 gallon bucket of produce breaks down into 3.5 gallons on about everything...rough rule of thumb ya know.