How to use this calculator
Generator fuel consumption changes with electrical load, engine size, maintenance, and fuel type. Use the manufacturer's consumption table at the expected load whenever possible.
- Choose expected continuous runtime.
- Find fuel use at your planned load.
- Enter the current price for the same fuel unit.
FORMULA
The math behind the estimate
runtime hours × fuel units per hour = fuel needed. Multiply by price per unit for operating cost.
Worked example
A generator using 0.75 gallons per hour for 24 hours needs 18 gallons and costs about $68 at $3.80 per gallon.
Change the defaults to model your home. The result is an estimate, not a guaranteed bill or savings promise.
How to read the result
Use the estimate to compare scenarios and find the inputs worth measuring more carefully. Utility bills can include fixed charges, taxes, delivery fees, minimums, tiers, and demand charges that are not fully represented by a simple energy rate.
Assumptions and limitations
- Fuel use is constant at the entered load.
- Maintenance and purchase cost are excluded.
- Safe outdoor placement and storage rules are essential.
Climate, equipment condition, installation, controls, and household behavior can materially change results. Verify consequential installation and purchasing decisions with qualified providers.
Practical savings context
Power only essential circuits and compare manufacturer half-load and full-load consumption before an outage.
SOURCE
Data and methodology
U.S. Department of Energy — Using Backup Generators
Safety guidance accessed August 2026. Geographic scope: United States. Last reviewed: August 6, 2026.
WattMeasure uses the source to frame the method and assumptions; your editable inputs determine the displayed result.
QUESTIONS
Generator fuel FAQ
How accurate is this generator estimate?
It is a planning estimate based on the values you enter. Actual power draw, cycling, utility charges, climate, and equipment condition can change the result.
Should I use the default electricity rate?
Your own marginal or all-in supply rate is better. Check a recent bill or your utility's published rate schedule.
Does this include taxes and utility fees?
Only when they are reflected in the rate you enter. Fixed monthly charges are not included because they usually do not change with one appliance's usage.
Last reviewed August 6, 2026 · Data update policy