How Long Does a BBQ Gas Bottle Last? 4kg vs 8.5kg Guide
The complete Australian guide to 4 kg and 8.5 kg LPG cylinders: realistic burn times at low, medium and high heat, how to estimate how much gas is left, and whether Swap 'n' Go or a refill works out cheaper.
The quick answer: a full 4 kg bottle lasts roughly 5–6 hours on a typical 3–4 burner barbecue at full heat, or 19–24 hours on low. A full 8.5 kg bottle lasts about 10–14 hours at full heat and 40–50 hours on low. Your real-world results depend on the barbecue's heat output, how many burners you run and the weather.
Why those numbers? Australian gas barbecues are rated in megajoules per hour (MJ/h) on the compliance plate, and a kilogram of LPG contains roughly 46–50 MJ of energy. A 4 kg bottle therefore stores about 190 MJ and an 8.5 kg bottle about 400 MJ. Divide the bottle's energy by your barbecue's burn rate and you have your burn time. If you are still choosing a grill, our best BBQ grills in Australia guide lists the burn rates of the most popular models.
How much gas does a barbecue actually use?
A compact two-burner barbecue such as the Weber Q 2200 (rated at about 19.4 MJ/h) sips gas, while a four-burner hooded unit rated at 40 MJ/h or more can empty an 8.5 kg bottle in a single long afternoon. You only hit the rated figure with every burner on full. At medium heat most cooks use roughly 40–60% of the rating, which is why burn times vary so much between households. Cold and windy days also increase consumption because more heat is lost to the air.
Burn time table: 4 kg vs 8.5 kg
| Cooking style | Typical burn rate | 4 kg bottle | 8.5 kg bottle |
|---|---|---|---|
| Low heat (a couple of burners, low) | ~8–10 MJ/h | ~19–24 hours | ~40–50 hours |
| Medium heat (all burners, medium) | ~15–20 MJ/h | ~10–13 hours | ~21–27 hours |
| High heat (all burners, full) | ~30–40 MJ/h | ~5–6 hours | ~10–14 hours |
Assumes a typical 3–4 burner hooded gas barbecue and full cylinders. On a compact two-burner like the Weber Q 2200 (19.4 MJ/h maximum), a 4 kg bottle lasts about 9–10 hours flat-out and an 8.5 kg bottle around 20 hours.
How to estimate how much gas is left
Running out mid-cook is the classic Aussie BBQ disaster, so here are the four most reliable ways to check.
- Weigh the bottle. The tare (empty) weight is stamped on the collar. Weigh the cylinder on bathroom scales and subtract the tare weight — the result is kilograms of LPG remaining. Multiply by roughly 47 MJ/kg and divide by your barbecue's burn rate to get hours left.
- The warm-water trick. Run warm water down the side of the cylinder. The metal feels cool below the gas level and warm above it — the boundary shows how full the bottle is. It works best on an empty-ish bottle.
- Use a gas gauge. Inline LPG gauges and magnetic level strips are cheap and reasonably accurate. Some newer BBQs include a gauge on the regulator.
- The shake test is unreliable. Sloshing tells you there is liquid inside, but not how much. Use it only as a rough "is it nearly empty?" check.
What should a full bottle weigh?
| Cylinder | Gas capacity | Typical tare weight | Approx. full weight |
|---|---|---|---|
| 4 kg bottle | 4 kg LPG | ~5.0 kg | ~9.0 kg |
| 8.5 kg bottle | 8.5 kg LPG | ~8.6 kg | ~17.1 kg |
Always use the tare weight stamped on your own cylinder's collar — brands differ by a few hundred grams.
Swap 'n' Go vs refill: which is better value?
In Australia you have two ways to keep a full bottle: swap it for a pre-filled exchange cylinder (Swap 'n' Go at Bunnings, Woolworths, servos and camping stores), or take your own cylinder to a gas outlet for a refill. As a rough guide in 2026:
| Option | Typical cost | Cost per kg (approx) | Best for |
|---|---|---|---|
| Swap 'n' Go — 4 kg exchange | ~$28–$33 | ~$7–$8 | Caravans, camping, Weber Q owners |
| Swap 'n' Go — 8.5 kg exchange | ~$34–$40 | ~$4–$4.70 | Convenience at Bunnings, Woolworths or servos |
| Refill — 8.5 kg at a gas outlet | ~$25–$35 | ~$3–$4 | Regular cooks who empty bottles often |
Exchange is more convenient and the bottle is always within its test date, but you pay a premium per kilogram and you do not own the cylinder. Refilling your own bottle is usually cheaper per kilogram — you only pay for the gas — but the bottle must be within its 10-year test date and you need a refiller nearby. If you barbecue weekly, the savings on refills add up over a summer; if you only cook occasionally, the convenience of Swap 'n' Go is worth the extra few dollars.
Gas bottle safety tips for Australian households
- Always use the cylinder outdoors in a well-ventilated area — never in a garage, shed or under the house, even with the door open.
- Keep the bottle upright and secure it in the barbecue trolley or against a wall so it cannot fall over.
- Check the test date stamped on the collar. Australian LPG cylinders must be retested or replaced within 10 years of the stamped date.
- Inspect the hose and regulator for cracks, kinks or perished rubber before each season, and replace a worn hose — typically every five years or sooner if damaged. If in doubt, call a licensed gasfitter.
- Leak-test with soapy water. Brush the connection points; bubbles mean a leak. Never use a flame to find a gas leak.
- Turn the cylinder valve off after every cook-up, not just the barbecue dials.
- Transport cylinders upright and secured, with the protective cap fitted, and never leave them in direct sunlight or a hot car.
- If you smell gas: turn off the valve if you can do so safely, do not operate switches, leave the area, and call your gas supplier — or Triple Zero (000) for the fire brigade in an emergency.
New to gas cooking? Our barbecue basics guide covers lighting, temperature control and cleaning, and our barbecue accessories guide lists the covers, brushes and thermometers worth buying.
Frequently asked questions
How long does a 4 kg gas bottle last?
On a typical 3–4 burner hooded barbecue, a full 4 kg bottle lasts about 5–6 hours at full heat, 10–13 hours at medium heat and 19–24 hours on low. On a compact two-burner such as the Weber Q 2200 it lasts about 9–10 hours flat-out.
How long does an 8.5 kg gas bottle last?
A full 8.5 kg bottle lasts roughly 10–14 hours at full heat, 21–27 hours at medium heat and 40–50 hours on low for a typical 3–4 burner hooded barbecue, and around 20 hours flat-out on a Weber Q 2200.
How do I check how much gas is left in my bottle?
The most reliable method is to weigh it: subtract the tare weight stamped on the collar from the current weight to get kilograms of gas remaining. The warm-water trick — run warm water down the side; the metal is cool below the gas level — is a good quick check.
Is Swap 'n' Go cheaper than getting my bottle refilled?
Usually not per kilogram. An 8.5 kg exchange costs roughly $34–$40, while refilling the same size costs about $25–$35 at a gas outlet. Swap 'n' Go wins on convenience and guaranteed in-test bottles; refilling wins on cost if you cook often.
How often do gas bottles need testing?
Australian LPG cylinders must be retested or replaced within 10 years of the date stamped on the collar. Swap 'n' Go bottles are maintained by the exchange company, so you never need to worry about the test date on an exchanged cylinder.