LPG Gas Bottle Calculator: How Long Will a 47kg Last?

If your range cooker or hob runs on bottled LPG, the question that matters is how often you will be swapping cylinders. The answer depends on energy, not guesswork: every kilogram of propane holds roughly 13.9 kWh of heat (butane about 13.7 kWh), so a burner's kW rating and how long it burns tells you how fast a bottle empties. Enter your appliance ratings and a typical day's cooking below to see how long one bottle, or a pair on an auto-changeover valve, should last, and what that gas costs you per day.

How the calculation works

Gas appliances in the UK carry a heat input rating in kW on their data badge. A 3 kW burner on full flame for one hour uses 3 kWh of energy. Divide that by the energy in a kilogram of LPG and you have the weight of gas burned: 3 kWh divided by 13.9 is about 0.22 kg of propane. The calculator repeats that sum for your hob and your oven, scales it by flame setting and thermostat cycling, averages it over the week, and divides the gas in your bottles by the daily figure.

Getting the inputs right

• Burner ratings: range cookers usually list each hob burner and oven in kW in the installation manual. A wok burner is often the largest; a simmer burner the smallest. Only add up the burners you actually light together.
• Flame setting: few people cook on full flame for long. Bringing a pan to the boil then turning it down averages out well below the burner's maximum.
• Oven on-time: a gas oven burns hard while it heats up, then the thermostat throttles the flame to hold temperature. Hotter ovens and frequent door opening keep the burner working harder.
• Twin bottles: with an automatic changeover valve the second bottle takes over when the first runs out, so enter 2 to see the total time before both are empty, then reorder as soon as the indicator flips.

Propane or butane?

Propane (usually red or orange bottles) keeps working in freezing weather, which is why it is the normal choice for cylinders stored outside a house. Butane (usually blue bottles) holds slightly more energy per litre but stops vaporising properly near freezing, so it suits indoor or summer use. Check that your cooker and regulator are set up for the gas you buy: they are not interchangeable without the right regulator, and conversion work must be done by a Gas Safe registered engineer.