How to measure the amount of LPG gas remaining in a cylinder | Simple Trick 2019
I am presuming that you are talking about domestic LPG cylinder in India.
The best method you can use is measuring the weight of the cylinder, this consist of two things weight of the cylinder itself and the weight of LPG gas in it, since the weight of empty cylinder is around 16 KG you will know the weight of liquid LPG inside the cylinder, typically the density of LPG in india is around 0.5-0.6 KG/liter (depending on the source of LPG), than you can use standard molar volume calculations to find out how much that LPG will occupy in standard pressure and temperature (typically for lighter LPG ie lower density same volume of liquid will result in more volume of gas at burner, around 500 m3 of gas for 1 m3 of liquid for a 50-50% mixture of propane and butane)
so a back of envelop calculation will be
volume at burner = ((M-16)/density)*500 liter LPG
where M - total weight of gas cylinder
typical value of density - 0.5-0.6 kg/liter
PS - a fresh LPG cylinder should give you around 13000 m3 gas at burner.
clarification : all calculation are ball park only