Generator Fuel Consumption: Diesel and Petrol Litres per Hour and Costs

Generator fuel consumption runs from 0.35 to 4.6 litres an hour across the petrol and diesel units we stock, depending on size and load. Twenty-four hours costs $17 to $256 in fuel. Here's the working on real generators.

Got a rough figure? That might be all you need. If you want the number for the machine you're eyeing, and what a blackout night or a week at camp costs, keep going.

Generator Fuel Consumption in Litres per Hour

Every figure below comes from each maker's own spec sheet. Take the litres a generator holds, divide by the hours it lasts at the output the maker tested, and you get its burn rate.

Petrol Inverter Generators (2-4.5kVA)

These are the small, quiet units you throw in the tray for camping and blackouts. On light work they barely sip.

Your real-world burn will usually be a bit hungrier than the brochure. Owners on Whirlpool and the Caravaners Forum keep landing on about a litre an hour once a mix of gear is cycling on and off. Plan your small petrol genny around that figure and you won't come up short.

You can compare the specs side by side in the petrol inverter generators range.

Open Frame Petrol Generators (8-12.5kVA)

Bigger open frame units burn more fuel, but they carry a lot more of it, so you refill less often.

One catch on the Champion. It only publishes a 12,500W figure with no separate continuous rating, so its 50% is half the headline number. Treat that one as a guide.

If you're setting up home backup, the WHXC8500E's 25 litres gets you through a night without a refill.

Diesel Generator Fuel Consumption (6.5-10kVA)

Diesel generators use less fuel for every kWh they make. They also cost you more up front, which our petrol vs diesel generator guide weighs up properly.

That last one is a 10kVA water-cooled standby unit. Flat out, it burns just over 4 litres an hour. You can compare tanks and outputs across the diesel generators range.

Litres per kWh: Diesel vs Petrol

A burn rate only tells you half the story, because more power always takes more fuel. Litres per kWh evens that out. It's the fuel you use for each unit of power you actually get.

Across the stocked generators in these tables and a few more, the middle diesel used 0.43 litres per kWh (seven units). The middle petrol reading was 0.73 (eight readings). So diesel used about 40% less fuel for the same power.

Diesel costs you more at the pump. The ACCC's early September 2026 averages for the five largest cities were $2.49 a litre for diesel and $2.05 for petrol, about 21% dearer. Each kWh still works out cheaper on diesel, at $1.08 against $1.49.

That only pays back a dearer diesel if you use it long and often. For a few blackouts a year, your cheaper petrol unit usually makes more sense.

Large Diesel Generator Fuel Consumption Charts

Most fuel consumption charts online start at 10kVA and climb into the thousands of kilowatts. They're built from big industrial sets doing steady heavy work. Those figures don't transfer to the portable generator in your shed.

What Changes Generator Fuel Consumption

It's 9pm and the power's been out since lunch. Your genny has been ticking over all arvo, keeping the fridge cold and a couple of lights on. You're starting to wonder if the fuel will last until morning.

Without the numbers, you're out there at 2am with a torch in your teeth, topping it up. If that load sits around a quarter of a Champion 2.5kVA's rating, its 4 litres last 11.5 hours. That's the fridge still cold at breakfast and nobody out of bed.

Load Percentage and Fuel per kWh

Load is the biggest lever you control. The Westinghouse iGen2600 shows it on its own spec sheet: 11 hours at 450W and 5.5 hours at 1,800W, from the same 5 litres.

That's four times the work for twice the fuel per hour. Flip it around, and the lighter job uses twice as much fuel for every kWh you get. A big generator loafing on a small job costs you more per unit of power than a small one working hard.

Light Loads and Idle Burn

Owners who've measured it back this up. A member of a US solar forum posted his test results for a fixed-speed petrol generator in 2011. Its fuel use flat-lined below about 20% load, because the motor burns a baseline just to keep spinning.

A Whirlpool member made the same point about a diesel sized for an aircon. He warned that running it for long with the aircon off is inefficient. If yours will spend a lot of time with almost nothing plugged in, read up on whether it hurts a generator to go without load first.

Working at Full Rated Output

Pushing flat out isn't the fix either. Some of the lowest fuel per kWh in the tables comes at 75-80% of rating. The Gentech ED6800YSRE at 0.38 litres per kWh is one.

Living at 100% has its own cost. One Whirlpool member warned that pushing close to max rated output for long periods is asking for trouble. Aim for about three-quarters, and keep the rest as headroom for your fridge compressor kicking in.

Inverter Eco Throttle vs Fixed-Speed Engines

A fixed-speed generator holds one speed, whatever you plug in. An inverter generator winds its engine back when demand drops. Westinghouse says so in its own FAQ, and recommends ECO throttle for long stretches at low or mid output to cut fuel use and wear.

Owners notice it at the jerry can. One Caravaners Forum member ran a fan heater about five hours a day off a 2,600W inverter on eco mode. That used about 3 litres of petrol a day. On that US solar forum, a 1,000W Honda inverter was reported lasting about 8 hours on a litre.

For camping and blackouts, where your gear switches on and off all day, that's fuel you keep for tomorrow.

Generator Size, Maintenance and Fuel Quality

Oversizing wastes your fuel quietly. A 12.5kVA generator powering your fridge sits at a tiny slice of its rating, right where fuel per kWh is worst. Size for what you'll really plug in, and our guide to what size generator you need walks you through it.

A clogged air filter or tired oil makes any generator work harder for the same power. Keep up your servicing and you'll get closer to the maker's figures.

Generator Fuel Costs and Time on a Tank

How to Calculate Generator Fuel Costs

Your fuel cost is the burn rate, times the hours you need it, times the price of a litre. Two steps get you there.

Step 1: Your Generator's Burn Rate

Use the tables above, or check your spec sheet for the litres it holds and the hours it lasts at a stated output. Divide litres by hours. If the maker doesn't say what it tested at, treat the figure as a light-work number and plan for more.

Step 2: Multiply by Hours and Fuel Price

Say you've got a Hyundai DHY6000SE at 50% for a shift of 7 hours. At 1 L/h, that's 7 litres. At $2.49 a litre, the shift costs you $17.43 in diesel.

Do that sum before the job, and you'll know how many jerry cans to throw in the ute.

Cost to Run a Generator 24 Hours a Day

Here's what a full day costs on each machine at its published output, at early September 2026 pump prices.

That's fuel only, and the refills column matters as much as the dollars. One Whirlpool household on petrol home backup reported burning about 20 litres of unleaded every 24 hours. That sits right inside this table.

Around-the-clock use is fine if you look after it. Westinghouse says its generators can keep going 24/7 when they're operated and maintained to the instructions. Always stop yours to refuel. There's more in the guide on whether a generator can run for 24 hours.

Not sure which way to go? Ring the store on 03 7056 6732, and we'll work through your loads with you.

Hours on a Tank of Fuel

How long your generator lasts comes down to what it holds and how fast it burns. The Gentech ED6800YSRE and ED8500KSRE are both diesels tested at 80%. The bigger one's 34 litres last 13 hours, against 3.3 hours from the smaller one's 5.4 litres.

That's close to four times as long before you reach for the jerry can. At 80%, the ED6800YSRE needs filling more than seven times across a full day.

Per litre, the spread is wide. A litre lasts just under 3 hours in the Champion 2.5kVA at 25%, and 2.2 hours in the iGen2600 at 450W. It lasts an hour in the Hyundai DHY6000SE at 50%, and just over half an hour in the Gentech ED6800YSRE at 80%.

Owners put it more simply. On that same Whirlpool thread, one member said the tank decides how long the generator keeps going. Pick yours for the longest stretch you'll be away from it.

Generator Battery Charging

Starter Battery Charging on Electric-Start Generators

Electric-start generators carry a 12V battery to crank the motor. Westinghouse confirms its 8500E and iGen4500 models are fitted with one. Whether that battery gets topped up while the generator runs varies by model, so check your owner's manual before you count on it.

If yours sits unused for months, give the battery a charge before you need it.

Generator Plus Battery for Light Overnight Loads

Plenty of owners who've done the sums skip an all-night generator. A fridge and some lights keep a big generator on light work for hours, which is its worst fuel per kWh.

Charging batteries through a generator loses a lot along the way, too. A Whirlpool member who measured his Honda EU20i worked out it turned about 11.5% of the fuel's energy into electricity. Commenters on a US YouTube test of a military diesel generator calculated about 21 to 23% of the fuel ending up in the battery.

The better play is a battery or a portable power station doing the night shift. Your generator then works hard for a couple of hours to top it up. Westinghouse notes that an off-grid system's inverter-charger can start a two-wire generator and recharge the battery automatically.

If your nights are only ever a fridge and lights, a power station on its own might mean the generator stays home.

Fuel Problems on Long Runs

Stale Fuel and Blocked Carburettors

Petrol left sitting in your generator goes off over time, and that's a classic cause of hard starting and rough running. Read up on whether you can leave fuel in your generator before it goes back on the shelf. Fresh fuel before a long job saves you pulling the carby apart.

Running Out of Fuel Under Load

Letting a tank go dry with everything still plugged in is worth avoiding, and there's a full guide on it in the reading below. Top up before you get low, with the generator switched off.

Wet Stacking on Lightly Loaded Diesels

Your diesel has a light-load problem of its own. Caterpillar's paper on generator set underloading says running below about 30% load for long periods leads to wet stacking, also called exhaust slobber. Caterpillar recommends at least 30% load for about 30 minutes in every four hours of light running.

Caterpillar is writing about big standby sets, but the principle carries over to a small diesel. The Whirlpool member above also warned that a diesel sized for the aircon will glaze its bores if it goes for long with the aircon off. If your diesel mostly ticks over through blackouts, give it a proper load now and then.

Want a second opinion on your setup? Ring the store on 03 7056 6732 or SMS 0476 330 590, and we'll sort the fuel side out with you.

More reading: what happens when a generator runs out of fuel, why your generator won't start and what fuel types generators use. Also worth a look: whether to store a generator full or empty and what an inverter generator is used for.