Generator Fuel Run-Time Calculator: Hours per Tank, Fuel per Day and Cost
Work out how long a generator runs on a tank, how much gasoline, propane or diesel an outage needs and what it costs, from the spec-sheet fuel use or estimated from the generator’s rated watts and load.
How it works
Run-time = tank ÷ fuel use · Cost per hour = fuel use × price · Fuel per day = fuel use × hours per day · Outage fuel = fuel per day × days · Estimated fuel use: gasoline = rated kW × (a + b × load), inverter a = 0.0304, b = 0.1245; conventional a = 0.0619, b = 0.1067 (gal/h); propane and diesel interpolated from published consumption charts by size and load
A generator’s run-time is its fuel supply divided by how fast it burns fuel, and the burn rate depends mostly on load. An engine still uses a good share of its full-load fuel when lightly loaded, so halving the load does not double the run-time: the Honda EU2200i inverter runs 8.1 hours on its 0.95 gal tank at ¼ load but 3.2 hours at its 1,800 W rating. If you know the fuel use from the spec sheet, enter it directly (tank size ÷ rated run time works too). Otherwise the calculator estimates it. For gasoline portables it uses a straight line per rated kilowatt fitted to Honda’s published run times: inverter models are more frugal at light load than open-frame (conventional) ones. For propane it interpolates a chart for air-cooled 10–26 kW standby units, and for diesel a widely used consumption chart for 20 kW to 2,250 kW generators; outside a chart’s range it scales per kilowatt. Treat estimates as ±15–30%. The daily figures multiply the hourly use by the hours you run each day, and the outage table shows how much fuel to store. Store gasoline with stabilizer and rotate it, keep propane cylinders upright outdoors, and always run the generator outside, well away from doors and windows.
Worked example
A 5-gallon tank at 0.75 gal/h runs 5 ÷ 0.75 = 6.7 hours (6 h 40 min). At $3.50 a gallon it costs 0.75 × $3.50 = $2.63 an hour. Running 12 hours a day uses 9.0 gallons, $31.50 a day, and a 3-day outage needs 27 gallons ($94.50), or 1.8 tank fills a day. Estimating instead: a 5,000 W conventional gasoline generator at 50% load uses about 5 × (0.0619 + 0.1067 × 0.5) = 0.58 gal/h, so the same tank lasts about 8.7 hours.
Sources: American Honda: EU2200i specifications (0.95 gal; 8.1 h at ¼ load, 3.2 h at rated load) · American Honda: EU7000iS specifications (5.1 gal; 16.0 h at ¼ load, 6.4 h at rated load) · American Honda: EB10000 specifications (8.19 gal; 7.9 h at ½ load, 5.4 h at rated load) · W Power Products: Approximate diesel fuel consumption chart · Portlandia Electric Supply: Generator fuel consumption chart (propane by kW and load)
Frequently asked questions
How long will a generator run on a tank of gas?
Divide the tank size by the fuel use at your load. A 5 gal tank at 0.75 gal/h lasts about 6.7 hours. Small inverter units run much longer at light load: Honda’s EU2200i is rated 8.1 hours at ¼ load on 0.95 gal, and its EU7000iS 16 hours at ¼ load on 5.1 gal.
How much fuel does a generator use per hour?
It scales with size and load. As a guide, a 5,000 W open-frame gasoline generator uses about 0.45 gal/h at ¼ load and 0.84 gal/h at full load; a 22 kW propane standby unit about 1.3 gal/h at ¼ load and 3.2 gal/h at full load; and a 100 kW diesel about 4.1 gal/h at half load. Use the estimate mode, or the spec sheet for your model.
How much fuel should I store for a power outage?
Multiply the daily fuel figure by the days you want to cover. Running a 0.75 gal/h generator 12 hours a day takes 9 gal a day, so 27 gal for three days. Store gasoline in approved containers with a stabilizer and rotate it; it degrades in a few months.
How long does a 20 lb propane tank last on a generator?
A 20 lb cylinder holds about 4.7 gal of propane. A small dual-fuel portable burning about 0.5 gal/h of propane at half load runs roughly 9 hours on it; a large standby unit drains it in 2 to 4 hours. Enter 4.7 gal as the tank and choose Propane to estimate.
Can I run a generator continuously?
Most portable generators need to stop to refuel and check oil, and you must let a gasoline unit cool before refueling. Inverter and standby generators tolerate longer runs. Always follow the manual, keep the generator outdoors and far from windows, and use a carbon monoxide alarm.
Does running at lower load save fuel?
Yes, but not proportionally. At light load the engine still burns fuel just to turn over, so a quarter load uses roughly 40–55% of full-load fuel. Inverter generators throttle down and save the most; staggering big loads such as a well pump and an air conditioner keeps the load, and fuel use, down.
Related calculators
Fuel figures are estimates. Generators produce deadly carbon monoxide: run them only outdoors, far from doors and windows, and follow the manufacturer’s instructions.