Step 1: add up the running loads
List everything that will run at the same time with its power in kW (from the nameplate) and add it up. Example: 3 AC units × 2.5 + kitchen 4 + lighting 0.8 = 12.3 kW.
Step 2: allow for the largest motor starting
AC units, pumps and compressors draw around three times their rating at start-up. Add twice the rating of your largest motor. In the example the largest motor is a 2.5 kW AC, so add 5, giving 17.3 kW.
Step 3: convert to kVA
Divide by a power factor of 0.8. In the example: 17.3 ÷ 0.8 = 21.6 kVA.
Step 4: add 20% headroom
A generator lasts longer and runs better below its maximum. 21.6 × 1.2 = 26 kVA, and the nearest standard size is 30 kVA.
Worked examples
| Case | Loads | Approx. size |
|---|---|---|
| Small camp | 1 AC, 2 floodlights, fridge | 15 kVA |
| Family camp | 3 AC, kitchen, pump, lighting | 30 kVA |
| Commercial camp | 6 AC, 2 kitchens, sound, lighting | 60 kVA |
| Construction site | Tower crane, 2 mixers, welder, office | 250 kVA |
Common mistakes
- Adding ratings without the starting current, so the unit trips when the AC kicks in
- Choosing a far bigger unit “to be safe”, which raises rental and diesel use
- Confusing kW with kVA
Common questions
What is the difference between kVA and kW?
kVA is the apparent power a generator is rated in; kW is the real power your equipment uses. kW ≈ kVA × 0.8.
What size does a house need?
It depends on the number of AC units. A house with four split units and basic appliances usually needs 20 to 30 kVA. Use the calculator for a closer figure.