Calculator
Estimate how much fuel a standby generator may consume and what it may cost to run — by outage duration, daily operation, or annual hours. Compare natural gas, propane, and diesel side by side.
Fuel Type
Calculation Mode
Enter how long the generator runs per day during an outage.
National average estimate: $1.20 per therm. Check your utility bill or recent delivery invoice for your local rate.
20 kW · 50% load · natural gas at $1.20 per therm
Estimated operating cost using your current generator size, load and fuel price.
Estimated hourly cost at national average prices · 20 kW at 50% load
$1.20 per therm
$2.50 per gallon
$3.80 per gallon
Comparison uses national average fuel prices.
Planning estimate only. Fuel consumption varies with load profile, ambient temperature, altitude, engine age, and maintenance condition. Monthly and annual projections in daily mode assume the generator runs every day at the selected hours — actual outage frequency in your area will determine realistic annual costs.
Where utility service is available, natural gas typically offers the lowest hourly operating cost and eliminates the need to manage an on-site fuel supply. Supply interruptions during major storm events are uncommon but possible in some areas — confirm reliability with your local utility.
Propane can be stored on-site for months without degradation, offering fuel security regardless of utility availability. It typically costs more per hour than natural gas, and tank capacity limits total runtime — plan for timely refills during extended outages.
Diesel generators can maintain strong efficiency under heavier loads and provide a reliable fuel supply independent of utilities. Diesel should be treated with a fuel stabilizer every 6–12 months when stored in standby tanks to prevent degradation.
