Example Data Table
| Generator kW |
Load kW |
Tank Liters |
Reserve |
Fuel Factor |
Expected Use |
| 3.5 |
1.8 |
15 |
10% |
360 g/kWh |
Light home backup |
| 5.0 |
3.0 |
20 |
10% |
340 g/kWh |
Mixed appliance load |
| 8.0 |
5.5 |
30 |
15% |
320 g/kWh |
Workshop operation |
Formula Used
Load from watts: Load kW = Watts / 1000.
Load from apparent power: Load kW = kVA × Power Factor.
Derated capacity: Capacity = Rated kW × (1 − Altitude Derate) × (1 − Temperature Derate).
Fuel burn: Liters per hour = Effective Load kW × BSFC ÷ Gasoline Density.
Usable fuel: Usable Liters = Tank Liters × (1 − Reserve Percent).
Runtime: Runtime Hours = Usable Liters ÷ Liters per Hour.
Trip fuel: Fuel Needed = Liters per Hour × Operating Hours.
Cost: Fuel Cost = Fuel Needed × Fuel Price per Liter.
How to Use This Calculator
Enter the generator rated power in kilowatts. Choose the load entry mode. Use watts for simple appliance totals. Use kVA and power factor for motors or mixed electrical loads.
Add the tank size, reserve level, operating time, fuel price, and consumption factor. Keep the default density unless you have a better local value. Use derating fields when the generator runs in hot or high-altitude conditions.
Press the calculate button. The result appears below the header and above the form. Download the result as CSV or PDF for planning, records, or client reports.
Gasoline Generator Fuel Planning
A gasoline generator is useful when grid power fails. It is also used on sites, farms, cabins, and events. Fuel planning prevents shutdowns. It also helps control cost. This calculator turns load data into practical fuel estimates. It uses rated power, actual load, tank size, fuel density, and reserve settings. It also considers altitude and temperature derating.
Why Fuel Use Changes
A generator does not burn fuel at one fixed rate. The burn rate changes with load. A light load still uses fuel because the engine must keep speed. A heavy load needs more torque, so it burns more gasoline. Power factor matters when loads are entered in volt amperes. Motors, pumps, and compressors can draw extra starting power. The tool lets you add a surge factor, so the plan is safer.
Runtime and Reserve Planning
Runtime is based on usable fuel, not total fuel. A reserve keeps fuel available for cooling, delays, and refueling errors. The calculator subtracts that reserve before estimating safe runtime. It also shows expected refills for a selected operating period. This helps plan overnight backup, work shifts, or emergency use. The cost result multiplies fuel volume by price.
Better Decisions
The output helps compare load levels. Lower load may extend runtime, but very low load can waste fuel. A balanced load often gives better efficiency and cleaner operation. The results can guide appliance scheduling. You can test several cases before buying fuel. You can also estimate how many tanks are needed for a long outage.
Math Based Estimates
The calculator uses brake specific fuel consumption. This value describes grams of fuel burned for each kilowatt hour produced. Gasoline density converts weight into liters. The method is flexible because users can change the efficiency assumption. It is still an estimate. Real fuel use can vary with engine age, maintenance, carburetor tuning, fuel quality, and weather.
Practical Use
Enter the generator rating first. Then enter the connected load. Use watts for simple loads, or use volt amperes with power factor. Add tank size, fuel price, operating hours, and reserve. Submit the form. Review burn rate, runtime, cost, derated capacity, load percentage, and refill count. Export results for records or for maintenance records later.
FAQs
What does this calculator estimate?
It estimates gasoline use per hour, runtime per tank, fuel needed, total cost, load percentage, surge percentage, and refill count.
Can I use watts instead of kVA?
Yes. Select watts when you know the actual running wattage. Select kVA when you also need to apply power factor.
What is BSFC?
BSFC means brake specific fuel consumption. It shows how many grams of fuel are used to produce one kilowatt hour.
Why does low load penalty matter?
Small engines may waste fuel at very light load. The penalty adds a simple adjustment for inefficient low-load operation.
What is usable tank fuel?
Usable fuel is total tank fuel after subtracting the selected reserve. It gives a safer runtime estimate.
Does altitude affect generator output?
Yes. High altitude can reduce engine power. Use the altitude derating field when the generator runs above normal conditions.
Is the result exact?
No. It is an estimate. Real fuel use depends on engine condition, maintenance, fuel quality, weather, and load changes.
Can I export the calculation?
Yes. After calculating, use the CSV or PDF button to save the result for planning or records.