How long will a generator run on 5 gallons of gas?

Five gallons is one standard gas can. How long it lasts depends on how big your generator is and how much you plug in. A small inverter at light load can go two days on it. A big open-frame generator working hard can use it up before bedtime.

The quick answer, by generator size

These come from makers' own spec pages. Each maker lists hours on a full tank at a stated load. We scaled each one to 5 gallons. The load % is a share of the running watts shown.

Generator (running watts)	Tank	Maker's run time	Hours per gallon	On 5 gallons
Small inverter (1,800 W)	1.14 gal	12 h at 25% load	10.5	~53 h
Small inverter (1,700 W)	1.1 gal	11.5 h at 25% load	10.5	~52 h
Mid-size inverter (3,500 W)	2.25 gal	14 h at 25% load	6.2	~31 h
Mid-size inverter (3,900 W)	3.4 gal	18 h at 25% load	5.3	~26 h
Large inverter (7,000 W)	5.33 gal	14 h at 25% load	2.6	~13 h
Open frame (3,500 W)	4.7 gal	14 h at 50% load	3.0	~15 h
Open frame (7,500 W)	6.6 gal	11 h at 25% load	1.7	~8 h
Open frame (9,500 W)	6.6 gal	12 h at 25% / 8 h at 50%	1.8 / 1.2	~9 h / ~6 h
Open frame (7,500 W)	7.7 gal	10 h at 50% load	1.3	~6.5 h

The sources below link each maker's page.

Two things jump out. Small generators run far longer, but they also carry far less. And a figure at 25% load looks much better than one at 50%. Compare like with like.

The math

Hours on 5 gallons = maker's hours on a full tank × (5 ÷ tank gallons)

Or, in two steps:

1. Hours per gallon = maker's hours ÷ tank gallons
2. Hours on 5 gallons = hours per gallon × 5

Worked example

One maker's generator rated 9,500 running watts has a 6.6-gallon tank. It lists 8 hours at 50% load, about 4,750 W.

• Hours per gallon: 8 ÷ 6.6 = 1.2
• On 5 gallons: 1.2 × 5 = about 6 hours
• Gas used per hour: 6.6 ÷ 8 = about 0.8 gallons

At 25% load, the same generator lists 12 hours. That's about 9 hours on 5 gallons.

The calculator above is pre-filled with this generator's numbers. Change the gallons or the load, or enter your own generator's figures from its manual.

What does "25% load" mean?

It's a quarter of the generator's running watts, not its peak watts.

Running watts	25% load	50% load
1,800 W	450 W	900 W
3,500 W	875 W	1,750 W
7,500 W	1,875 W	3,750 W

So "53 hours on 5 gallons" from a small 1,800 W inverter assumes you're only drawing about 450 W. That's a fridge and a few lights, not much more. It also means refilling its small tank four or five times.

Why more load doesn't mean a straight line

The 9,500 W open-frame model lists 12 hours at 25% and 8 hours at 50%. Doubling the load cut run time by only a third. An engine burns some fuel just to keep itself turning, whatever you plug in.

Inverter generators save the most here. Their engines slow down when the load is light. A conventional generator runs at a steady speed. That's why the inverters in the table get so many more hours per gallon at 25% load. See inverter vs conventional generators.

How to make 5 gallons last longer

• Only run what you need. A closed fridge stays cold for a while, so you can run the generator a few hours at a time instead of all day.
• Stagger big loads. Don't start the well pump and microwave at once.
• Use eco mode if your inverter has it.
• Skip heating loads if you can. Space heaters and electric water heaters are big, steady draws.
• Right-size the generator. A huge generator running a small load wastes fuel. Our size calculator helps.

Refueling and storing gas safely

• Shut the generator off and let it cool before you refuel. OSHA warns that fuel spilled on hot engine parts can ignite.
• Store gas in approved, labeled, vented containers, away from the generator and any flame. Don't store it in your home.
• Old gas causes trouble. Generac recommends draining the tank and running the carburetor dry if you'll store the generator more than 30 days.

Gas or propane?

Many generators are dual-fuel. Propane doesn't go stale, but it gives about 10% less power and fewer hours per gallon. Compare them in our propane tank run-time guide.

Whatever the fuel, run your generator outdoors only, at least 20 feet from your home, with the exhaust pointed away from windows and doors. Read our generator carbon monoxide safety guide.