Generator Fuel Consumption: What Actually Determines It

Why there's no single number

Fuel consumption depends on the generator's size, how much load it's actually carrying, and the fuel type, so any single gallons-per-hour figure you see online is only accurate for one specific unit at one specific load. Your installer can give you the real number from the manufacturer's spec sheet for the exact model they're proposing.

What holds true across units

• Load matters more than generator size alone. A generator running at half load burns meaningfully less fuel than the same unit at full load, this is true across brands and fuel types.
• [Natural gas](/guides/natural-gas-vs-propane-generator) has effectively unlimited run time. Since it draws from the utility gas line rather than an on-site tank, consumption rate matters for your gas bill, not for how long the generator can run.
• [Propane and diesel](/guides/natural-gas-vs-propane-generator) are tank-limited. A larger on-site tank extends run time, but also costs more upfront and takes more yard space. Tank sizing is part of a proper installation quote, not something to guess at.
• [Portable generators](/glossary/portable-generator) typically need the most frequent refueling, since their tanks are small relative to a standby unit's on-site propane tank.

What to ask your installer

Ask for the specific model's fuel consumption at 50% and 100% load from the manufacturer spec sheet, and, if you're on propane or diesel, ask them to size the tank against your realistic run-time expectations for your area's typical outage length, not just the generator's rated capacity.