How Long Does a 45kg Gas Bottle Last? A Household Worksheet

How long does a 45kg gas bottle last? The answer changes dramatically depending on whether it supplies a cooktop, daily showers or winter space heating. A useful estimate starts with those appliances and their operating time, then leaves room for uncertainty. It should help you order in time, not encourage you to run the supply to its limit.

Quick answer

How long a 45kg gas bottle lasts depends on the appliances using it and their daily operating time. Estimate days by dividing the bottle’s approximate energy content by total daily gas consumption. Cooking alone can use much less than space heating or hot water, so another household’s delivery interval is not a reliable forecast for yours.

How long does a 45kg gas bottle last in your household?

Start by listing every appliance connected to the LPG supply. Include hot water and heating even if you mainly think of the bottles as “cooking gas”. Check the appliance manual or rating information for gas input, usually shown in megajoules per hour, rather than guessing from physical size.

Write down how long each appliance actually runs. A heater switched on for an evening may cycle or modulate; a continuous-flow hot-water unit generally consumes gas while delivering heated water, not for the entire day. Your estimate needs the relevant operating time and input, with uncertainty acknowledged.

If the appliance label is inaccessible, use the model documentation or ask the supplier. Do not remove protective panels or interfere with gas fittings to obtain a number. This guide concerns budgeting and delivery planning, not appliance servicing.

Choose a transparent energy assumption

Elgas’s calculation guide uses approximately 49 MJ per kilogram of propane, giving 2,205 MJ for 45kg. Supagas’s home LPG guide rounds to 50 MJ per kilogram, giving 2,250 MJ. The difference illustrates why a planning calculation should not claim precision down to an exact hour.

For the worked examples below, we use a rounded 2,200 MJ per full 45kg bottle. This is a stated calculation assumption, not a test of a delivered cylinder or a guarantee of usable supply under every operating condition.

The basic formula is bottle energy divided by daily gas input. Keep MJ separate from MJ/h: one is an amount of energy, the other is the rate at which an appliance uses it. Multiply the rate by hours before dividing the bottle energy.

A single-appliance example

Suppose a hypothetical heater has a gas input of 20 MJ/h and operates at that input for three hours a day. Daily consumption is 20 × 3 = 60 MJ. A 2,200 MJ bottle would then represent roughly 37 days of that use.

If it ran for only one hour a day at the same input, the calculation would give about 110 days. Neither result is a household average. The example simply shows why operating hours matter as much as the bottle size.

Do not substitute heat output in kW for gas input without understanding efficiency and units. Useful room heat is not the same quantity as energy taken from the cylinder. Where the manual gives several input settings, use the setting that matches your assumption.

Add appliances by daily consumption

A home with cooking and hot water needs a combined estimate. Adding appliance ratings alone is not enough because the appliances rarely run for identical lengths of time. Calculate a daily amount for each, then add those amounts.

At 78 MJ a day, 2,200 MJ represents about 28 days. Without the heater, the same assumed cooking and hot-water use totals 42 MJ a day, giving about 52 days. This is an original example using invented appliance inputs and durations, not a prediction for a family of a particular size.

Why hot-water estimates can be uncertain

Hot-water demand depends on how much water is heated and the temperature rise required. Visitors, longer showers and colder incoming water can increase consumption without any appliance fault. A unit’s maximum input is not necessarily its input throughout every shower.

For a simple first estimate, clearly label maximum-input calculations as such. If you need a tighter forecast, ask the manufacturer or supplier about the unit’s operating behaviour and use your own consumption history. Do not turn down stored-water temperatures or change safety settings purely to meet a gas budget.

Cooking is variable too. Several burners at different settings do not equal one burner running at maximum. A record of typical use is usually more honest than a precise-looking total based on a single remembered meal.

Use your delivery history as a cross-check

Keep delivery dates, bottle quantities and the dates a bottle became empty or was changed over. Delivery date alone may not equal the start of consumption if the bottle sat in reserve. Note whether a returned bottle still contained gas.

If a full bottle supplied the same appliances for 55 days, the implied average using our planning assumption is about 40 MJ a day. Compare that with your worksheet. A large difference may mean an appliance was omitted, runtime was overstated or the observation period was unusual.

Repeat the comparison across seasons. A cooking-only household may be steadier than one with space heating. Do not project a mild month across the coldest part of the year and call the result a reliable delivery schedule.

Two bottles and automatic changeover

Many household installations use a working bottle and a reserve. Understand your particular arrangement through the supplier’s instructions. Automatic changeover can maintain supply, but it can also make it less obvious that the first bottle has emptied.

Do not assume that seeing two cylinders means you have two full cylinders. Record what was delivered and ask how to recognise when the reserve is in use. Arrange replacement with enough lead time for the route serving your address.

Avoid disconnecting, relocating or attempting to refill a household cylinder yourself. Supplier-managed equipment and fixed gas installations involve safety and ownership requirements. Our LPG refill versus bottle exchange guide explains the service choices without treating them as DIY tasks.

Leave a delivery buffer

Ask your supplier about ordinary lead times, regional delivery days, holiday arrangements and any urgent-delivery charges. An estimate of 28 days does not mean day 27 is the right time to place an order. Weather and changes in use can move the result.

For a hypothetical five-day lead time at 78 MJ a day, those five days represent 390 MJ of planned use. You would want enough supply to cover the lead time plus a sensible margin, confirmed against the actual cylinder arrangement. The calculation does not tell you how to measure the remaining gas safely.

If the property will host visitors or become occupied after a long vacancy, notify the supplier when that affects an automatic delivery schedule. A forecast based on an empty holiday home may not fit a fully occupied week.

Turn the duration estimate into a budget

Once you have a reasonable annual quantity, multiply by the quoted fuel cost and add equipment rental or service charges, delivery and other applicable fees. Keep the price of a full bottle separate from a promotional credit that applies only to an early order.

At an invented $150 per 45kg bottle, four bottles cost $600 before annual charges, while eight cost $1,200. Those figures are not market quotes. They show why uncertainty in annual quantity can outweigh a modest difference in the price of one bottle.

For the broader fuel decision, see mains gas versus LPG. If comparing suppliers, use our LPG switching checklist to include equipment ownership and return arrangements as well as price.

When to ask for help

An unexplained change in duration deserves attention, but do not diagnose a leak from arithmetic alone. Check the household’s usage history and ask the supplier to investigate concerns. Any suspected gas leak takes priority over the cost calculation: move to safety and contact the appropriate emergency service from a safe location.

Sources and review

The CompareUs Editorial Team checked Elgas and Supagas on 28 September 2026. Supplier conversion assumptions differ slightly; the examples deliberately use a rounded figure and are labelled hypothetical. Confirm appliance ratings, safe monitoring and delivery arrangements with your supplier.