So, scaling up, we have a litre with a mass of 493 grams or 1.1 Pounds
Or, put in reverse to answer you question, 0.91 Litres = 1 pound
I'm not exactly sure how much propane weighs. You could weigh an empty propane contain, log that weight. Next you would weigh a container with propane in it. You then would subtract the weight of the container and you would have your answer. Hopefully this will help.
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