Calor Gas 5kg, 13kg Patio Gas cylinders and 6kg propane Lites are fitted with Calor's new Gas Trac - an indicator which tells you when you are running low on gas. For all other cylinders, the empty tare weight can be found on a metal disc on the shroud, this gives the weight of the cylinder in pounds and ounces. To convert this to kilograms multiply this number by 0.453592. Once you have the empty weight of the cylinder you weigh the full cylinder on scales, then subtract the empty weight from the cylinder weight. This will give you the weight of gas left in the cylinder, which can then be compared with a full cylinder, e.g. 15kg.