The capacity of an LPG cylinder used at home can vary depending on the size of the cylinder. LPG cylinders come in a range of sizes from small portable BBQ gas cylinders to large tanks. The most common size for domestic use is the 45kg LPG gas cylinder, and a typical installation would include two 45kg gas bottles connected in tandem. A changeover lever allows you to switch between bottles, so when one empties, you can change over to the new one ensuring you have an uninterrupted gas supply. The 45kg gas bottle remains the most common domestic LPG gas bottle-cylinder used in homes across Australia, mainly because of its manoeuvrable size and versatility, it can be used for heating, hot water, and cooking. Cylinder capacity is generally expressed in litres or kilograms. A good conversion rate to remember for cylinder capacity is that 1 kilogram is approximately equal to 1.96 litres of LPG. The formula to calculate cylinder capacity is the formula for cylinder volume. Cylinder capacity volume = πr²h. However, because of the LPG 20% allowance for ullage, you must subtract 20% from the overall cylinder volume. So, the formula changes for LPG: LPG cylinder capacity volume = (πr²h)×.80.