Tools
Diesel generator size calculator
Enter the loads that run at the same time and the largest motor you need to start. The calculator converts kW to kVA, allows for altitude and heat, adds a reserve, and shows which of our models cover the result. Every step is shown, so you can check the figures yourself.
Result
Required generator size
14.4kVAprime power
Includes 15% reserve · 50 Hz · Single-phase
How we got there
- 1Running load
- 10 kW
- 2Peak load with motor start
- 10 kW
- 3In kVA at PF 0.8
- 12.5 kVA
- 4After altitude and heat derating (0%)
- 12.5 kVA
- 5With 15% reserve
- 14.4 kVA
- Current at 230 V
- 62.6 A
Want an engineer to check it against your actual loads?
Send these results to an engineer →WhatsAppModels that cover this load
Prime power at 50 Hz, Single-phase. Standby power is higher. Size on prime for daily running.
- Closest match
How the calculator works
It follows the same five steps as our generator sizing guide. Add the loads that run together. Add the starting surge of the largest motor. Divide by the power factor to get kVA. Allow for altitude and heat. Then add a reserve for loads you will add later.
The altitude rule is about 3% less output for every 300 m above 1,000 m. The heat rule is about 2% for every 5 °C above 40 °C. Both come from our guide to diesel derating at altitude.
Prime or standby?
The models shown are matched on prime power, the rating for daily running. Standby power is about 10% higher and is meant for emergency use only. If the set will run every day, size on prime. Our guide on prime and standby power explains the difference.
Want the whole chart?
The kVA size chart lists common loads with their kW, kVA and current, so you can check a result against typical equipment.
Questions
- How do I convert kW to kVA?
- Divide kW by the power factor. At a power factor of 0.8, 16 kW is 20 kVA.
- How much bigger should the generator be than my load?
- Size for the peak, including the largest motor start, then add 10 to 20% reserve. At altitude or in heat, size for the derated output.
- Why does a pump need a bigger generator than its rating?
- A motor draws 3 to 7 times its running power for a moment when it starts. The generator has to supply that peak without the voltage collapsing.