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Generator Fuel & Runtime Calculator

Your generator, your load, your fuel → gallons per hour, hours per tank or cylinder, dollars per day — and what a generator kilowatt-hour really costs.

By Brian Hamilton · Updated

Your generator where to find theseedit in My Rig →
Type
Where the fuel is

Generator, AC, converter and fuel tank come from My Rig when saved; changes here save back. The sheet figures are optional — Honda prints hours per tank at ¼ and rated load (divide the tank by each); Cummins prints gal/h at no, half and full load (enter the full-load one).

Load presets from your rig

Load is the average watts while the generator runs — an AC that cycles 60% of the time is a 900 W load, not 1,500. The presets read your AC and converter from My Rig. Hours, price and fuel on hand are today's question and aren't saved.

Fuel & runtime

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Enter your generator's rated watts and a load.

    How much gas does an RV generator use per hour?

    It depends on the load, and a "0.3–0.7 gallons an hour" range is that dependence with the load left out. Fuel burn is close to a straight line from the no-load burn, the fuel it takes just to spin the engine at 3,600 rpm, to the full-load burn, and the makers publish the endpoints. Cummins prints no / half / full figures for its onboard sets (the Onan QG 4000 and QG 5500 sheets); Honda prints hours per tank at ¼ and rated load for the EU2200i. On that line, the three generators most RVers own:

    LoadHonda EU2200i (inverter, 1,800 W)Onan QG 4000 (onboard, 4,000 W)Onan QG 5500 (onboard, 5,500 W)
    No load (idling)0.06 gal/h · 17.4 h/gal0.28 gal/h · 3.6 h/gal0.36 gal/h · 2.8 h/gal
    25%0.12 gal/h · 8.5 h/gal0.38 gal/h · 2.6 h/gal0.50 gal/h · 2 h/gal
    50%0.18 gal/h · 5.6 h/gal0.49 gal/h · 2 h/gal0.63 gal/h · 1.6 h/gal
    75%0.24 gal/h · 4.2 h/gal0.59 gal/h · 1.7 h/gal0.77 gal/h · 1.3 h/gal
    100%0.30 gal/h · 3.4 h/gal · 3.2 h/tank0.70 gal/h · 1.4 h/gal0.90 gal/h · 1.1 h/gal

    Gasoline. EU2200i: the line through Honda's two tank figures (0.95 gal: 8.1 h at ¼ load, 3.2 h at rated). Onan QG 4000 and 5500: Cummins' full-load figures (0.7 and 0.9 gal/h) with a 40% no-load share. Against the sheets' own no-load and half-load points, the line gives 0.28 / 0.49 for the QG 4000 (sheet 0.3 / 0.5) and 0.36 / 0.63 for the QG 5500 (sheet 0.3 / 0.6), so it runs a little high at idle on the bigger set.

    The no-load row is the price of running at all. An Onan 4000 idling with nothing plugged in burns 0.28 gal/h, which is 40% of what it burns flat out, so at light loads most of the fuel goes to the engine, not the electricity. The tool shows that share as the idle tax for your set and your load.

    How long will a generator run on a gallon of gas?

    LoadHonda EU2200iOnan QG 4000Onan QG 5500
    Lights, fans, fridge board (300 W)10.3 h per gal · 0.10 gal/h3.2 h per gal · 0.31 gal/h2.6 h per gal · 0.39 gal/h
    Charging the bank (55 A converter) (932 W)5.5 h per gal · 0.18 gal/h2.6 h per gal · 0.38 gal/h2.2 h per gal · 0.45 gal/h
    13,500 BTU AC running (1,500 W)3.9 h per gal · 0.26 gal/h2.3 h per gal · 0.44 gal/h2 h per gal · 0.51 gal/h
    AC + converter (2,432 W)over its rating1.9 h per gal · 0.54 gal/h1.7 h per gal · 0.60 gal/h
    Two ACs + converter (3,932 W)over its rating1.4 h per gal · 0.69 gal/h1.3 h per gal · 0.75 gal/h

    13,500 BTU AC at 1,500 W running (EER 9); converter at 55 A = 932 W from the generator (14.4 V ÷ 85%). "Over its rating" = the load exceeds the set's running watts; the AC's start surge is the generator-size page's question.

    Read the AC row across: the same 1,500 W costs 0.26 gal/h on the Honda and 0.44 on the Onan 4000. The Onan is a bigger engine carrying the same load, and 64% of its fuel at that load is the no-load burn. An inverter set of the Onan's size at the same load would burn about 0.35 gal/h. That gap is what a "big" inverter generator buys over an onboard 3,600 rpm set.

    Why an inverter generator uses less fuel at light load

    A conventional generator has to spin at 3,600 rpm to make 60 Hz, whatever the load; its no-load burn is the fuel that speed costs. An inverter generator makes DC and synthesizes the 60 Hz electronically, so its engine can slow down when the load is light ("eco throttle"), and the no-load burn falls to about a fifth of full load instead of a third to a half. At full load the two are the same engine doing the same work. The difference sits at the light end: the 300 W of lights, fans and fridge board in the table above costs 0.10 gal/h on the EU2200i and 0.31 on an Onan 4000, 3.2× as much. Without a data sheet the tool assumes 20% / 40% for the two types and says so.

    How long will an RV generator run on a tank — and the quarter-tank rule

    A portable's tank is the whole answer: the EU2200i's 0.95 gal at 0.26 gal/h is 3 h 42 min of air conditioning, or 9 h 46 min of the 300 W lights, fans and fridge board. An onboard set draws from the motorhome's chassis tank through a pickup tube that sits above the bottom. It stops drawing at about a quarter tank, so you can't run the generator until the coach won't start. The tool counts only the fuel above that line: a 55 gal tank is 41 gal of generator fuel, which at the AC load is 3 d 22 h, or 11.8 days at 8 hours a day, before the generator quits and the coach still drives. Fill the chassis tank before the boondock.

    How much does it cost to run an RV generator?

    Per hour is the easy number; per kilowatt-hour is the one you can set against the pedestal. At the AC load and $3.50 gasoline:

    Running a 1,500 W ACgal/h$/hour8 h daykWh per gal$/kWh
    Honda EU2200i0.26$0.90$7.205.8$0.60
    Onan QG 40000.44$1.53$12.253.4$1.02
    Onan QG 55000.51$1.78$14.203$1.18
    The pedestal, metered—$0.26$2.04—$0.17

    Gasoline at $3.50/gal; a gallon holds 33.4 kWh and a small generator turns about 18% of it into electricity at full load, less at part load because the no-load burn is fixed. Pedestal at the US residential average of $0.17/kWh; most campgrounds bundle it.

    A generator kilowatt-hour costs 3.5 to 7.0 times a pedestal one

    Running the AC, the EU2200i delivers 5.8 kWh per gallon, $0.60 per kWh at $3.50 gas; the Onan 4000 3.4 kWh, $1.02; the Onan 5500 3 kWh, $1.18. The pedestal is $0.17. Refilling a 2 × 100 Ah lithium bank from its 20% floor through a 55 A converter takes 3 h 22 min of generator at 932 W, which is $4.45 of gasoline on the Onan 4000. A 400 W roof puts the same 2,048 Wh back in 1.6 average days with no fuel at all, and the solar calculator sizes that roof for your state.

    How long does a generator run on a 20 lb propane tank?

    Propane carries 20% less energy per gallon than gasoline, and a dual-fuel set makes about 10% less power on it (Champion's 201122: 1,850 W running on gas, 1,665 W on propane), so the cylinder hours are shorter than the gasoline hours per gallon suggest. A 20 lb cylinder you refill yourself holds 4.7 gal. An exchange cylinder holds less: Blue Rhino's own FAQ gives 15 lb net, a fill the FTC's 2014 settlement records Blue Rhino and AmeriGas cutting from 17 lb to 15 lb in 2008, which is 3.5 gal. On a dual-fuel 3,500 W set:

    Loadgal/h propane20 lb, refilled15 lb exchange30 lb40 lb, or two 20s
    500 W0.3513 h 23 min10 h 2 min20 h 5 min26 h 46 min
    1,500 W0.489 h 54 min7 h 25 min14 h 50 min19 h 47 min
    2,500 W0.607 h 51 min5 h 53 min11 h 46 min15 h 42 min

    3,500 W conventional dual-fuel set on propane, from fuel energy (26.8 kWh/gal at 18%) with a 40% no-load share. Two refilled 20s hold the same 40 lb as one 40 lb cylinder, so they share a column. Two checks on the model: it lands 5% above the full-load LP burn on Cummins' QG 5500 sheet (4.6 lb/h, 1.08 gal/h), and for Champion's 201122 at 25% load it gives 34.2 h on a 20 lb cylinder against Champion's "up to 34 hours". Those are the same cylinders the furnace and fridge draw from; the propane page budgets all of it together.

    The generator on propane is the exchange-cylinder trap: at 0.48 gal/h an AC night empties a refilled 20 lb cylinder in 9 h 54 min and an exchange cylinder in 7 h 25 min, and at a $25 exchange (this page's planning price) the 15 lb fill works out to $7.07 a gallon before the derate. Propane is the clean, storable fuel for the emergency set at home. On the road, at the same price per gallon, gasoline carries 25% more energy per dollar, and the propane is better kept for the furnace; the charge-time calculator says how many generator hours the bank needs in the first place.

    Sources

    1. Honda EU2200i Super Quiet Series Generator Technical Specifications, American Honda Motor Co.: DC output 12 V, 100 W (8.3 A)
    2. RV QG 4000 Specification Sheet, Cummins (Onan): Gasoline 0.3 / 0.5 / 0.7 gal/h at no / half / full load; LP 1.5 / 2.4 / 3.1 lb/h; output falls 3.5% per 1,000 ft
    3. RV QG 5500 Specification Sheet, Cummins (Onan): Gasoline 0.3 / 0.6 / 0.9 gal/h at no / half / full load; LP 1.8 / 3.3 / 4.6 lb/h; output falls 3.5% per 1,000 ft
    4. 2500-Watt Dual Fuel Inverter, model 201122, Champion Power Equipment: up to 34 hours at 25% load on a 20 lb cylinder
    5. How much propane does Blue Rhino put in its tanks?, Blue Rhino: exchange cylinders hold 15 lb of propane, net
    6. Blue Rhino, AmeriGas Settle FTC Charges of Restraining Competition, Federal Trade Commission: the 2008 cut in exchange fills from 17 lb to 15 lb