How Much Does It Cost to Run a Generator?
About $2.48 an hour — 0.75 gallons of gasoline — for a 7.5 kW portable carrying half its nameplate at $3.30 a gallon. A full day of outage costs $59.47 and 18.02 gallons. The number that matters more, though, is what that makes a kilowatt-hour worth: 66¢, about 4.1× the 16¢ the grid charges for the identical electricity. Set your generator, your load and your fuel price below.
Running watts on the nameplate, not the surge figure.
The load, not the generator. This is what sets the bill.
What almost every portable runs on. You have to store it, and it goes stale.
What you actually pay, which is the only price that matters.
Generator
Load on it
On a day it runs at all. Most people shut it off overnight.
Leave at 0 if it only runs in real outages — then read the table below instead.
What the same power would have cost, had the power been on.
Fuel cost per hour
$2.48
0.75 gallons an hour at $3.30/gallon, carrying 3.75 kW (50% of the nameplate) — which works out at 66¢ a kilowatt-hour. The grid sells you the same kilowatt-hour for 16¢.
Cost per kWh generated
66¢
4.1× the 16¢ grid rate
Per day it runs (12 h)
$29.73
9.01 gallons of fuel
Same power from the grid
$0.60
an hour — what the outage is really costing you
No monthly or annual figure — good. A home generator does not run on a schedule; it runs when the power fails, and nobody knows how often that will be. Multiplying an hourly cost by a month you invented is how most generator “running cost” numbers are made up. Price a real outage instead — the table below does — or, if yours genuinely does run every day (off-grid, job site, RV), set “days a month” above and the monthly and annual figures will appear here.
What an outage costs, running this load right through it
| Outage | Fuel | Fuel cost | From the grid |
|---|---|---|---|
| An afternoon4 hours | 3.00 gal | $9.91 | $2.40 |
| A long evening12 hours | 9.01 gal | $29.73 | $7.20 |
| A full day24 hours | 18.02 gal | $59.47 | $14.40 |
| Three days72 hours | 54.06 gal | $178.40 | $43.20 |
| A week168 hours | 126 gal | $416.28 | $100.80 |
Fuel only. A generator running through a week-long outage also wants an oil change, and if it is a portable running on gasoline you have to physically find 126 gallons during a storm, which is the part nobody plans for.
$0.83 an hour of that buys you nothing
A generator holds 3,600 rpm to hold 60 Hz whether it is carrying your house or carrying nothing at all, and that costs fuel — about $0.83 an hour on this machine, which is 33% of your $2.48 hourly bill at this load. It is why running a big generator lightly loaded is so expensive per kilowatt-hour, and why the cheapest thing you can do in an outage is put moreon the generator while it is already running, not less — do the laundry, run the dishwasher, charge everything. The engine is burning that fuel regardless.
Fuel burn is modelled as a straight line with a lift at zero — the no-load burn plus a share proportional to load — calibrated so it reproduces the tank sizes and 50%-load runtimes manufacturers publish. It is a model, not a measurement: your manual's consumption figure beats it, and you can check this one against it by setting the load to half the nameplate. Grid rates come from the average rates by state page.
How much does it cost to run a whole-home generator?
$2.17 an hour — $52.11 for a full day — for a 22 kW standby on natural gas, carrying a real 5 kW house.
That is 1.45 therms an hour at $1.50/therm, and it works out at 43¢ a kilowatt-hour — 2.7× what the grid charges. It is the cheapest generated electricity on this page, and it is still nearly three times the price of the electricity you were buying yesterday.
Worked example (22 kW standby, 5 kW load, $1.50/therm): the engine burns 1.45 therms an hour = $2.17 an hour, = $52.11 a day, while delivering 5 kWh an hour. The same 5 kWh from the grid would have cost $0.80.
The load sets the bill, not the size of the generator
This is the thing most generator running-cost pages get wrong, and it is not a small error. A generator's engine has to spin at 3,600 rpm to hold 60 Hz whether it is carrying your whole house or a single lamp, so its fuel curve is a line with a lift at zero, not a line through the origin: it burns roughly a fifth of its full-load fuel doing nothing. Which means a lightly-loaded generator makes staggeringly expensive electricity — and a whole-home standby carrying a real house is, by design, lightly loaded. That 22 kW machine above is using $1.14 of its $2.17 hourly fuel bill — 52% of it — just holding 3,600 rpm. You are paying for the headroom to start the well pump, every hour, whether the well pump starts or not.
| On a 7.5 kW portable, gasoline | Fuel | Per hour | Per kWh made | vs the grid |
|---|---|---|---|---|
| Just the fridge300 W — The load almost everyone starts with — and the most expensive kilowatt-hour on this page | 0.29 gal/hr | $0.96 | $3.19 | 20.0× |
| Fridge, lights, wifi900 W — Keeping the food cold and the phones charged | 0.37 gal/hr | $1.22 | $1.36 | 8.5× |
| Essentials + furnace blower2500 W — Add the sump pump and the heating, which is what winter outages are about | 0.58 gal/hr | $1.93 | 77¢ | 4.8× |
| Most of the house5000 W — Essentials plus a well pump, the water heater or a window AC | 0.92 gal/hr | $3.03 | 61¢ | 3.8× |
| Half the nameplate3750 W — The load spec sheets quote runtimes at | 0.75 gal/hr | $2.48 | 66¢ | 4.1× |
Read the top row twice. A 7.5 kW generator kept running for nothing but the fridge burns 0.29 gallons an hour — $0.96 — to deliver 300 watts. That is $3.19 a kilowatt-hour, or 20× the grid rate, and it is the most expensive electricity anywhere on this website. The fix is not to run the generator less; it is to put more on it while it is running. Do the laundry, run the dishwasher, charge every device in the house. The engine is burning that fuel anyway.
What an outage actually costs
Ignore “monthly cost”. A home generator does not run on a schedule — it runs when the power fails, and the only honest unit is the outage. Both machines below are carrying the same 5 kW house, right through.
| Outage | 7.5 kW portable, gasoline | 22 kW standby, natural gas | Had the grid been up |
|---|---|---|---|
| An afternoon4 hours | $12.113.67 gal | $8.695.79 therms | $3.20 |
| A long evening12 hours | $36.3411.01 gal | $26.0617.37 therms | $9.60 |
| A full day24 hours | $72.6822.03 gal | $52.1134.74 therms | $19.20 |
| Three days72 hours | $218.0566.08 gal | $156.33104 therms | $57.60 |
| A week168 hours | $508.78154 gal | $364.77243 therms | $134.40 |
Fuel only. The week-long row is the one worth staring at: the portable needs 154 gallons of gasoline, which you have to physically find, in a storm, with the pumps at every station also on a generator. The standby needs nothing — the gas is already piped to the house, which is most of what you are actually paying for when you buy one.
Portable vs standby generator running costs
Judged the only fair way — every machine below is carrying the same 5 kW house, so the difference is the machine and its fuel, not the job it is doing.
| Machine | Fuel an hour | Cost an hour | Per kWh | A day of outage |
|---|---|---|---|---|
| Mid-size portable, gasoline7.5 kW — cords through a window | 0.92 gal | $3.03 | 61¢ | $72.68 |
| Large portable, gasoline12 kW — through a transfer switch | 1.01 gal | $3.33 | 67¢ | $79.88 |
| Whole-home standby, propane22 kW — from a buried tank | 1.52 gal | $3.79 | 76¢ | $90.93 |
| Whole-home standby, natural gas22 kW — piped, never runs out | 1.45 therm | $2.17 | 43¢ | $52.11 |
The fuel decides this, not the machine
The standby wins — 43¢ against 61¢ — but put that same standby on propane instead of piped gas and it becomes the most expensive machine in the table at 76¢. Nothing about the engine changed. What changed is what a BTU costs:
| Fuel | Price | Energy in it | Per million BTU |
|---|---|---|---|
| Gasoline | $3.30/gallon | 120,286 BTU | $27.43 |
| Propane | $2.50/gallon | 91,452 BTU | $27.34 |
| Natural gas | $1.50/therm | 100,000 BTU | $15.00 |
Piped natural gas costs about 45% less per unit of energy than anything you carry in a can, and that gap is the entire reason a standby generator is cheap to run. Note also that gasoline and propane land within a few cents of each other — $27.43 against $27.34— because propane's cheaper gallon holds correspondingly less energy in it. Anyone telling you propane is the cheaper fuel is comparing the price per gallon and stopping there. Prices are this site's defaults (the same ones the furnace and EV charging pages use); put yours into the calculator and the ranking may well change.
A standby generator bills you in years when the power never fails
This is the running cost nobody mentions. A standby generator starts itself, runs unloaded for a few minutes and shuts down — once a week, forever — because that is how it knows it will start on the night it matters. At a common 12-minute exercise cycle that is 10.4 hours of running a year, burning roughly 7.9 therms and costing $11.83 a year on natural gas — $20.64on propane — to produce no electricity at all. It is cheap for what it buys you, and it is genuinely the correct trade. But it is not zero, which is what “it only runs during outages” quietly implies.
Buying propane the expensive way
A dual-fuel portable run off barbecue cylinders is the worst of both worlds, and the arithmetic is brutal because propane is sold by weight in a cylinder and by volume in a tank. Propane weighs about 4.24 lb a gallon, so a “20 lb” cylinder holds only about 4.7 gallons. Swap one for $25 and you have paid $5.30 a gallon — about 2.1× the delivered price — and on a 7.5 kW portable carrying 5 kW you would empty roughly one cylinder every 3.7 hours. If you are going to run a generator on propane, the tank in the ground is the whole point of it.
Generator vs battery backup cost comparison
A generator makeselectricity out of fuel. A home battery does not make anything — it stores electricity you already bought from the grid at the grid's price. That single distinction decides the entire cost comparison, and it decides it very one-sidedly.
Home battery
18¢
per kWh — grid power, plus the round trip
Standby, natural gas
43¢
per kWh — 2.4× the battery
Portable, gasoline
61¢
per kWh — 3.4× the battery
The battery's energy is cheap. Its problem is that it runs out.
A kilowatt-hour out of a home battery costs whatever you paid the utility for it, plus the little the round trip through the cells loses on the way — around 90% comes back, so 16¢ in becomes about 18¢ out (17¢ to 19¢ if that round trip is as good as 95% or as bad as 85%). That is a fraction of what any engine can do. But a battery holds a fixed number of kilowatt-hours, and when they are gone the thing it recharges from is the grid — which is the thing that just failed. A generator has no such limit: it runs for exactly as long as you can keep feeding it. You are not really comparing two prices. You are comparing cheap-but-finite energy with expensive-but-indefinite energy.
Solar is what makes a battery a real answer
Pair the battery with panels and the arithmetic changes completely: the roof refills it every morning without asking the grid's permission, and the marginal kilowatt-hour costs nothing to generate. That is the only version of battery backup that survives a multi-day outage, and it is the honest comparison against a standby generator — not battery-versus-generator, but solar-plus-battery versus generator. This page prices fuel, not hardware; what the two systems cost to buy and install is a different question with a much wider spread, and we are not going to invent a figure for it.
A battery sitting idle costs nothing. A generator idling does not.
It is worth putting these two facts next to each other, because they are the same fact from opposite ends. A battery draws essentially nothing while it waits; a standby generator burns $11.83 a year just proving to itself that it still starts, and once running it burns $0.83 an hour on a 7.5 kW portable before it delivers a single watt — 33% of the bill even at half load. If your outages are short and shallow, the battery is not just cheaper per kilowatt-hour, it is cheaper full stop. If they are long, none of that matters and you want the engine.
Related Guides
Cost to Run a Space Heater
1,500 W — the load people reach for in an outage, and the one a small generator hates
Cost to Run a Sump Pump
The one appliance whose failure during an outage costs more than the generator
Solar Panel Savings
The other way to make your own electricity — and the one that refills a battery
Most Efficient Appliances
What to put on the generator first, when every watt costs 66¢
How to Save on Energy Bills
Practical tips by room, with the savings priced
Electricity Rates by State
The rate your generated power is competing with
Frequently Asked Questions
How much does it cost to run a generator per hour?
A 7.5 kW portable on gasoline, carrying half its nameplate (3.75 kW), burns about 0.75 gallons an hour — $2.48 an hour at $3.30 a gallon. That works out at 66¢ per kilowatt-hour, about 4.1 times the 16¢ the grid charges for exactly the same electricity. The single biggest thing that moves this number is not the generator, it is the load: the same machine carrying only a fridge costs $3.19 a kilowatt-hour, because the engine burns nearly as much fuel either way.
How much does it cost to run a whole-home generator?
A 22 kW standby generator on natural gas, carrying a real 5 kW house, burns about 1.45 therms an hour — $2.17 an hour, or $52.11 for a full day of outage at $1.50 a therm. That is 43¢ a kilowatt-hour, 2.7 times the grid rate — the cheapest generated electricity on this page, because piped natural gas costs about 45% less per unit of energy than gasoline. On propane the same generator and the same house would cost $3.79 an hour.
How much fuel does a generator use per hour?
Roughly 0.75 gallons an hour for a 7.5 kW portable at half load, which is the figure manufacturers quote runtimes at — a 7.5 kW machine with a seven-gallon tank is being sold as "about ten hours" on that basis. Fuel burn tracks the load, not the size of the generator, but not proportionally: the engine has to spin at 3,600 rpm to hold 60 Hz whether it is carrying your house or nothing at all, so it burns roughly a fifth of its full-load fuel with nothing plugged in. On this machine that is $0.83 an hour of fuel that buys you no electricity whatsoever.
Is it cheaper to run a generator on propane or gasoline?
At typical prices they are close to a wash, which surprises people who only look at the price per gallon. Propane is cheaper by the gallon — $2.50 against $3.30 — but a gallon of it holds about a quarter less energy, and those two effects very nearly cancel: $27.34 against $27.43 per million BTU. Propane's real advantages are that it stores indefinitely without going stale and it does not gum up a carburettor. Its real disadvantage is how you buy it: bulk delivered propane at $2.50 a gallon and a swapped 20-pound cylinder are the same molecule at very different prices, because a cylinder holds only about 4.7 gallons — a $25 swap is $5.30 a gallon, roughly 2.1 times the delivered price.
Is a standby generator cheaper to run than a portable?
Per kilowatt-hour, yes — but the fuel is doing the work, not the machine. Carrying the same 5 kW house, a 7.5 kW portable on gasoline costs 61¢ a kilowatt-hour and a 22 kW standby on natural gas costs 43¢. Put that same standby on propane, though, and it costs 76¢ — more than the portable. A standby's engine is genuinely a little more efficient, being bigger, but what actually decides this is that piped natural gas is about 45% cheaper per unit of energy than anything you carry in a can.
Is battery backup cheaper to run than a generator?
Much cheaper per kilowatt-hour, because a battery does not make electricity — it stores electricity you already bought at the grid rate. Allowing for a round trip through the cells of about 90%, a kilowatt-hour out of a home battery costs about 18¢ against 61¢ from a gasoline portable — around 3.4 times less. The catch is not the price, it is the duration: a battery holds a fixed number of kilowatt-hours and the thing it recharges from is the grid that has just failed. A generator runs for as long as you can keep feeding it. Pair a battery with solar and it refills itself, which is the only version of this that runs indefinitely.
Does a generator burn fuel with nothing plugged into it?
Yes, and more than people expect. The engine holds 3,600 rpm to hold 60 Hz regardless of load, so it burns roughly a fifth of its full-load fuel doing nothing — $0.83 an hour on a 7.5 kW portable, which is 33% of its hourly bill even when it is carrying half its nameplate. The practical consequence is the opposite of what most outage advice says: while the generator is already running, the cheapest thing you can do is put more on it, not less. The marginal kilowatt-hour is far cheaper than the average one.
What does a standby generator cost to run if the power never goes out?
About $11.83 a year on natural gas, and it is a line almost nobody budgets for. A standby generator starts itself, runs unloaded for a few minutes and shuts down once a week, every week, so that it knows it will start when you actually need it. At a common 12-minute exercise cycle that is 10.4 hours of running a year and roughly 7.9 therms of gas, burned to produce no electricity at all. On propane the same self-test costs about $20.64 a year. It is the price of the thing starting reliably, and it is cheap for what it is — but it is not zero, which is what "it only runs in an outage" implies.