Run time rating (at 25% / 50% load)
Generator runtimes are quoted at a fraction of rated load — usually 25% or 50% — on a full tank. A “12 hours at 50%” unit running near full load may manage only 5–6 hours, so match the load fraction to how you will actually use it.
Fuel burn does not scale linearly with load: engine overhead means quarter-load burn is roughly 60–65% of half-load burn, not half. That is why the 25% figure is not simply double the 50% figure on spec sheets that publish both.
Marketing favors the 25% number because it is biggest. For outage planning, the 50% figure is usually the honest one — a refrigerator, furnace, lights, and electronics put a mid-size generator near half load.