How long will your generator run, and how much will it cost? Enter your generator size and fuel type to get runtime estimates, daily fuel costs, and tank sizing recommendations.
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Natural gas generators run indefinitely — they connect to your utility supply line and don't run out. This calculator focuses on runtime for propane and diesel tanks, and fuel cost for all types.
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Generator Details
$/gal
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BTU/hr at load
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Gal/hr consumed
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Daily fuel cost
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5-day outage cost
Tank Runtime at Your Load
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Natural gas generators don't run out of fuel. They connect directly to your utility supply line. Runtime is limited only by maintenance intervals — typically 200–500 hours between oil changes, depending on the model. Your primary cost is the gas consumed, billed through your utility at your standard rate.
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Fuel Cost Comparison Over a 5-Day Outage
Fuel Type
Typical Consumption (20kW, 75% load)
5-Day Cost Estimate
Pros
Cons
Natural gas
~130 cu ft/hr → utility billing
$50–$120
Unlimited supply; lowest operating cost
Requires gas service; line may fail in disasters
Propane (500 gal)
~1.8 gal/hr → ~60 hrs runtime
$250–$450
No utility dependency; stores indefinitely
Tank runs dry; refill needed for long outages
Diesel
~1.5 gal/hr → varies by tank
$200–$400
High energy density; stable storage
Diesel degrades after 12 months; CA air quality permits
Propane Tank Sizing Guide
Choosing the right propane tank size is critical. Run out during a multi-day outage and the generator stops. Most installers recommend sizing your tank for at least 5–7 days of runtime at 75% load.
Generator Size
Consumption @ 75% load
100 gal tank
250 gal tank
500 gal tank
Recommended
10 kW
0.9 gal/hr
~111 hrs (4.6 days)
~278 hrs (11.5 days)
~556 hrs (23 days)
250 gal
16 kW
1.4 gal/hr
~71 hrs (3 days)
~179 hrs (7.5 days)
~357 hrs (15 days)
250–500 gal
20 kW
1.8 gal/hr
~56 hrs (2.3 days)
~139 hrs (5.8 days)
~278 hrs (11.5 days)
500 gal
22 kW
2.0 gal/hr
~50 hrs (2 days)
~125 hrs (5.2 days)
~250 hrs (10.4 days)
500 gal
30 kW
2.7 gal/hr
~37 hrs (1.5 days)
~93 hrs (3.9 days)
~185 hrs (7.7 days)
500–1,000 gal
Assumes 60% propane is usable (tanks should not be drawn below 20% for proper pressure). Consumption rates are approximate at 75% load.
Disclaimer: Fuel consumption estimates are approximate based on typical generator efficiencies at stated load percentages. Actual consumption varies by model, ambient temperature, altitude, and load composition. Always consult your generator's installation manual for model-specific fuel consumption data.