Generator Fuel Calculator
Generator gas in gallons or liters plus tank hours from load.
What it does
Outages turn on fuel math. The fridge, furnace fan, and a few lights set a steady kilowatt load, and hours times load set the can count.
The tool above divides energy by 8 kWh per gallon. A 3.5 kW load for 8 hours needs 3.5 gal, or 1 can, with 11.4 hours per 5 gal tank. The metric match is 13.2 L.
The 8 divisor fits small gasoline units at part load. Full load burns more per kWh, eco mode burns less, and diesel follows a different curve in the manual.
Tank hours pace the night. Eleven hours per tank means one evening fill covers sleep, while a 7 kW load halves that and needs a 3 am plan.
Cans and safety close the loop. Store rated cans outside living space, cool the unit before refueling, and run it outdoors far from windows.
How to use
- Pick imperial (gal) or metric (L).
- Enter average load in kW.
- Enter run hours.
- Read fuel first.
- Read can count next.
- Read hours per tank and plan refills.
Formula
- load
- Average electric load.
- hours
- Run hours.
Liters convert at 3.78541 per gallon. Cans are 5 gal imperial and 20 L metric, with tank hours shared.
Worked example
Example: 3.5 kW for 8 hours
Imperial defaults: 3.5 kW for 8 hours. These are also the default values, so the page opens on this answer.
- Load: 3.5 kW.
- Time: 8 hours.
- Energy: 3.5 x 8 = 28 kWh.
- Fuel: 28 / 8 = 3.5 gal.
- Cans: ceil(3.5 / 5) = 1 can (5 gal).
- Tank: 5 x 8 / 3.5 = 11.4 hours per tank. Tool shows 3.5 gal, 1 can (5 gal), 11.4 hours per tank.
Reference table
| Load | Hours | Fuel |
|---|---|---|
| 2 kW | 8 | 2 gal |
| 3.5 kW | 8 | 3.5 gal |
| 5 kW | 10 | 6.3 gal |
| 3.5 kW | 24 | 10.5 gal |
Limits
- Estimate only. Load swings and surge shift burn.
- Gasoline part load assumed. Diesel differs.
- Ignores oil, cords, and transfer gear.
- CO safety needs placement rules.
Common mistakes
- Sizing fuel at nameplate instead of average load.
- Forgetting surge on well pumps and saws.
- Refueling a hot unit.
- Running indoors or near windows.
- Storing summer gas for winter storms.
Try it yourself
Quick checks. Answers sit tucked under each question.
5 kW for 10 hours?
5 x 10 / 8 = 6.3 gal after rounding (6.25). Cans are ceil(6.25 / 5) = 2 cans.
2 kW for 24 hours?
2 x 24 / 8 = 6 gal. Tank hours are 5 x 8 / 2 = 20 hours per tank.
Questions
How much fuel for 8 hours?
Multiply kW by hours, then divide by 8. Here 3.5 x 8 / 8 = 3.5 gal.
What is the 8 divisor?
Near 8 kWh per gallon for small gasoline units at part load. Diesel and large units differ, so check the manual curve.
How long per tank?
Divide tank gallons by the same rate. A 5 gal tank at 3.5 kW gives 5 x 8 / 3.5 = 11.4 hours.
How many cans?
Round up to full cans. Here ceil(3.5 / 5) = 1 can.
Does surge matter?
Yes. Surge at motor starts burns extra, and eco mode saves at light load.
Does this wire the house?
No. Transfer switches, cords, and CO safety need their own plans.