How to use it
- Find two numbers in the manual: fuel tank size, and runtime per tank. The runtime is always quoted at a stated load, such as "10 hours at 50% load".
- Pick your unit. Switching between US gallons and litres converts the tank and container sizes for you.
- Enter hours per day. Few people run a generator around the clock. Running it in blocks to chill the fridge and recharge devices saves a lot of fuel.
- Enter the outage length you want to be ready for.
The formula
burn rate = tank size ÷ runtime per tank
fuel needed = burn rate × hours per day × days
With the starting numbers, 3.4 gallons ÷ 10 hours is 0.34 gallons an hour. Over 8 hours a day for 3 days that is 0.34 × 24 = 8.2 US gallons, or about 30.9 litres: three tank fills, and two 5-gallon cans.
How run time changes the total
| Hours per day | 1 day | 3 days | 7 days |
|---|---|---|---|
| 4 | 1.4 gal | 4.1 gal | 9.5 gal |
| 8 | 2.7 gal | 8.2 gal | 19.0 gal |
| 24 | 8.2 gal | 24.5 gal | 57.1 gal |
These figures use the same example generator at 0.34 gallons an hour. Running all day for a week takes more fuel than most homes can store safely, which is the case for running in blocks.
Reading the result
- Fuel for the outage is the total to have on hand, shown in both units.
- Tank fills tells you how often you will refuel. Always shut the generator down and let it cool first.
- Containers is the total fuel divided by your can size, rounded up.
Propane and dual-fuel generators
Use the same method with the propane figures from the manual. A standard 20 lb barbecue cylinder holds about 4.7 US gallons (roughly 17.8 litres) of propane when full, so enter 4.7 as the tank size and the manual's runtime for a 20 lb cylinder. Propane stores for years without going stale, which makes it a good standby fuel.
Storing fuel safely
- Keep gasoline in approved containers, outside the living space and away from any flame, pilot light or heater.
- Local fire codes limit how much you may store at home. Check yours before buying extra cans.
- Gasoline goes stale. Add fuel stabilizer and rotate it through a car or mower every few months.
- Never refuel a hot or running generator.
Common questions
My load is different from the load in the spec. Does that matter?
Yes. Fuel use rises with load. If the manual quotes runtime at 25% load and you will run at 50%, expect a noticeably shorter runtime. Use the figure for the load closest to yours.
Is an inverter generator more efficient?
Usually, at light loads. An inverter generator slows its engine when demand is low, while a conventional generator holds a fixed speed.
How do I find my real burn rate?
Fill the tank, run your normal outage loads, and time how long it lasts. Enter that as the runtime per tank.
Related
Reviewed October 2026. Results are planning estimates. Check them against your equipment's specifications. Report a problem.