Generator Fuel Cost per kWh Calculator
Estimate camper generator energy cost from rated watts, load percentage, fuel type, fuel burn curve, fuel price, runtime, charger efficiency, altitude derate, and maintenance allowance.
Calculation breakdown
| Generator setup | 25% load | 50% load | 75% to 100% load | Planning note |
|---|---|---|---|---|
| 2,000 to 2,200 W inverter gasoline | 0.10 to 0.14 gal/hr | 0.17 to 0.22 gal/hr | 0.28 to 0.45 gal/hr | Good fit for converter charging and small AC loads when the camper is not running a roof AC. |
| 3,000 to 3,500 W inverter gasoline | 0.16 to 0.22 gal/hr | 0.28 to 0.38 gal/hr | 0.48 to 0.75 gal/hr | Often a middle ground for one air conditioner, charger, and short kitchen loads. |
| 4,000 to 4,500 W open-frame gasoline | 0.25 to 0.35 gal/hr | 0.45 to 0.60 gal/hr | 0.70 to 0.98 gal/hr | Higher idle and noise can raise cost per kWh on light camper loads. |
| 4,000 W propane RV generator | 0.30 to 0.45 gal/hr | 0.55 to 0.75 gal/hr | 0.85 to 1.30 gal/hr | Propane stores cleanly but usually burns more gallons for the same electric output. |
| 5,500 W onboard gasoline generator | 0.35 to 0.50 gal/hr | 0.55 to 0.75 gal/hr | 0.85 to 1.20 gal/hr | Efficient enough with steady coach loads, costly when lightly loaded for charging only. |
| 7,500 to 8,000 W diesel onboard | 0.22 to 0.35 gal/hr | 0.38 to 0.55 gal/hr | 0.65 to 0.95 gal/hr | Usually strongest under larger continuous loads in diesel motorhomes. |
| Elevation | 3.5% per 1,000 ft derate | 3,500 W rated output | What to check |
|---|---|---|---|
| Sea level | 0% | 3,500 W available | Use nameplate continuous watts for the load percentage basis. |
| 3,000 ft | 10.5% | 3,133 W available | Startup surge and roof AC headroom begin to matter more. |
| 6,000 ft | 21% | 2,765 W available | Reduce simultaneous loads or use a larger generator rating. |
| 9,000 ft | 31.5% | 2,398 W available | High draw appliances may no longer fit even if they work at low elevation. |
| Use case | Typical efficiency | 1 generator kWh becomes | Planning note |
|---|---|---|---|
| Direct AC appliance load | 95% to 100% | 0.95 to 1.00 useful kWh | Use 100% only when measuring AC energy directly at the appliance. |
| RV converter to lead-acid bank | 78% to 88% | 0.78 to 0.88 battery kWh | Absorption taper can make the last part of charge look expensive. |
| Inverter charger to lithium bank | 88% to 94% | 0.88 to 0.94 battery kWh | Strong for bulk charging if the generator is loaded into an efficient range. |
| Small charger on oversized generator | 80% to 90% | 0.80 to 0.90 battery kWh | Electrical efficiency may be fine while fuel kWh cost is poor from light load. |
| Allowance | Typical included items | Best fit | Cost effect |
|---|---|---|---|
| $0.03 to $0.06/hr | Oil reserve and basic wear allowance | Small inverter generator used occasionally | Adds only a few cents per delivered kWh at moderate load. |
| $0.08 to $0.15/hr | Oil, plug, air filter, fuel stabilizer, service parts | Regular weekend boondocking and camper charging | Good default when fuel cost is not the only ownership cost. |
| $0.20 to $0.40/hr | Heavier service reserve and shop labor planning | Onboard RV generators or rental fleet use | Can noticeably change the cost per kWh result. |
| $0.50/hr and up | Major service reserve, high-hour depreciation | Commercial or full-time generator dependence | Use when the generator is a primary power source. |
Small Inverter
Best for battery charging, laptops, fans, and quiet low loads. Cost per kWh rises if a charger pulls far below the efficient load band.
Mid Inverter
A practical single-AC camper choice. It can hold a better load percentage when charging and running a few AC appliances together.
Onboard Propane
Convenient for RV tanks and cold storage. It often costs more per delivered kWh, so charger efficiency and runtime matter.
Diesel Coach
Strong under steady high loads in larger rigs. It may beat small generators per kWh when air conditioning and charging run together.
altitude derate factor = 1 - (elevation feet / 1000 x derate percent / 100), limited to a practical minimum.effective watts = rated watts x derate factor; running watts = effective watts x load percent / 100.fuel burn is linearly interpolated between the 25%, 50%, 75%, and 100% burn curve points, then converted from L/hr to gal/hr if needed.delivered kWh = running watts x runtime hours / 1000 x charger efficiency.total cost = fuel gallons x fuel price + runtime hours x maintenance allowance; cost per kWh = total cost / delivered kWh.
You fill up your tank and drive off into some remote campground with plans to camp out under the stars…with the lights on. First couple of nights are great and then later you get your memory card receipt from the remote gas station. You see the price per kilowatt hour.
It’s not just numbers on a page. It’s whether you enjoy this boondocking adventure or question why you’re paying so much more to camp than stay at a hotel.
Why Your Generator Costs More Than You Think
Folks most think there is one variable, fuel cost. But what really happens is where that fuel becomes usable battery power before it ever gets to your RV. Plug in the data into the calculator above, which will do the number crunching for you, but knowing what it’s measuring makes all the difference when you’re operating your system.
For example, consider the load percentage. Idling a truck down the highway is like running a big generator at 20% load. Even though electrical need may be small, engine is still burning fuel just to maintain operation. This is an inefficient use of fuel and dramatically increase your cost per kilowatt-hour. To account for this, enter your fuel burn rates at different load points into the tool. It then uses those values to find middle points and show what it actualy costs to run your system the way you do. Maybe you’ve been trickling power into your batteries over six hours and you find out that charging them harder for less time is more economical. The math doesn’t lie that much about wasting money.
Most owners don’t think about altitude until their air conditioner trips the breaker, but it’s a quiet factor in the equation. As you ascend, air becomes thinner and an engine require air to fully combust fuel. According to the reference table on the page, most gasoline and propane generators loses approximately 3.5 percent of their power for every 1,000 feet above sea level. So if you’re at 6,000 feet, you’re losing more than 20 percent of your available watts. Your generator will have to do the same job with less, which changes the fuel efficiency curve. Derating it means it has to work harder in relation to its capacity. It can’t just run the same numbers it did at sea level.
And then there’s the loss that comes from converting electricity. When you’re running something like a hairdryer straight off an outlet, you get almost 100% of the generator output. When you’re charging your battery bank, however, the power must first go through your inverter charger or converter. Those things is good and efficient, but they aren’t perfect. An inverter charger will lose somewhere around 10-15% of its energy as heat. So you paid for that energy in terms of fuel, but it never made it to your batteries. You can account for that loss and have a better idea of what you’re actualy paying for each kilowatt-hour of electricity, which makes your numbers appear more rosy if you don’t adjust for that.
The silent tax on generators is maintenance. There are oil changes, air filters, spark plugs and ultimately service required on the engine itself. Spread this out as an hourly charge based off how many hours you operate it and you’ve got a full accounting of operating expenses. Adding a couple cents to the bottom line will do nothing if running for one hour makes no difference between diesel, gasoline, or propane. But if you run for multiple hours then that dollar amount add up. In some respects, diesel engines is more thermally efficient at load than gas, but initial fuel costs are higher. Similarly, propane is cleaner and convenient, but it burns much more to produce the same electric power. It’s all about your load profile and how long you run it.
Bottom line, we want our generator size to fit the task at hand. Trickle-charging a small battery bank with a giant on-board generator would of bankrupt you. Not only does it burn more fuel than necessary; it’s obnoxious and uncool.
Right-sizing your power generation means operating the generator within its best load band, typically between 40-70 percent, thereby lowering the cost per kilowatt-hour to something reasonable. You will no longer fret over the gas pump; instead, enjoy the silence in the campground once more. That’s what makes the math work.
