Generator Size & Fuel Consumption Calculator
Add up your factory's connected load to find the generator size you need, then see how much diesel, gas or petrol it burns and what a day of load-shedding costs you.
Generator size & fuel
Size a generator for your factory and see what it burns.
Connected load
The biggest motor sets the starting surge. Blank assumes one motor carries the total.
Blank uses an indicative price.
Enter your connected load to size a generator.
How this is calculated
- 1
Convert each load to kVA
Motors at 0.746 kW per HP with 85% efficiency and 0.8 power factor (about 1.1 kVA per HP). Lights and fans at 0.9 power factor. Air conditioners at about 1.5 kVA per ton. Welders at the kVA you enter.
- 2
Add a 20% safety buffer
Running a generator flat out shortens its life and leaves no room for starting currents. The running load is increased by 20%.
- 3
Check the motor starting surge
The largest motor needs about 3 times its running kVA to start direct on line, 1.75 times with star-delta and 1.2 times with a VFD or soft starter. If that surge is bigger than the buffered load, it sets the size.
- 4
Fuel consumption
Modelled from typical generator fuel charts: a fixed no-load burn plus fuel per kW delivered. A diesel set uses about 0.28 litres per kWh at full load and more per unit at light load.
Frequently asked questions
What size generator do I need for a 10 HP motor?
A 10 HP motor runs at about 11 kVA. With star-delta starting it needs roughly 20 kVA to start, and direct on line about 33 kVA, so a 20 to 30 kVA set is typical when it is the only load.
How much diesel does a 100 kVA generator use?
Roughly 12 litres an hour at half load, 17 at three-quarter load and 22 at full load. Older or poorly maintained engines use more.
What is the difference between kVA and kW?
kW is the real power your machines use; kVA is what the generator must supply including reactive power. Generators are rated at 0.8 power factor, so 100 kVA gives 80 kW.
Can I run welding machines on a generator?
Yes, but welders draw sharp, uneven current. Size generously, prefer inverter welders, and avoid running them on a generator that is already near full load.