Only at the load the maker quoted it at, which is usually a fraction of the rated output. At full load the same tank empties considerably faster, and two runtime figures are comparable only if both name the same load.
Runtime is the figure most often compared and most often compared wrongly, because it is not a property of the tank alone.
The load is half the specification
A runtime quoted at a quarter load and one quoted at full load describe the same machine differently. When the load is not stated, the figure cannot be checked and cannot be compared; when it is, the comparison is straightforward.
Why engine type changes the curve
A conventional generator runs its engine at a fixed speed to hold the output frequency, so consumption falls only modestly as the load drops. An inverter generator decouples engine speed from output frequency, so light loads cost much less fuel. The advantage is real and it is largest exactly where most household backup sits.
What else the tank decides
Refuelling frequency during a long outage, and therefore how often the machine must be stopped and allowed to cool — which every manual specifies and which is not optional.
The figures worth writing down
Rated output, maximum output, runtime with its load, noise with its distance, and the fuel the engine takes. Five numbers, each meaningless without its qualifier, and each published by makers who intend them to be compared.
What people ask before they order
Does an inverter generator change the arithmetic?
It can, because the engine speed follows the load instead of holding a fixed speed. At light loads that reduces consumption noticeably, which is why the quoted load matters even more on these machines.
What about fuel stored between outages?
Petrol degrades in storage, and makers publish instructions for storage, stabilisers and draining before a long idle period. Those instructions are per engine and they are the reference.
Last reviewed 16 September 2026