Undersized generators cause voltage drops and equipment damage. Oversized ones waste fuel. This calculator helps you find the right fit.
kVA = Total Watts ÷ (PF × 1000). Add 25% margin for safety.
Motors draw 3–6× running watts during startup. Include the largest surge.
Home backup, construction sites, events, industrial standby power.
Add all running watts + largest starting watt surge, then divide by PF × 1000.
Calculate minimum generator capacity.
PF is typically 0.80 for standby generators. Add 25% margin to the result for recommended size.
4 steps to the right generator.
Write down running wattage of every device that will run simultaneously.
Add the largest starting surge (motors typically need 3× running watts to start).
Divide total watts by PF (0.80 standby, 0.85 prime) to get kVA.
Multiply by 1.25 for the recommended generator size.
Common appliance wattages for sizing.
| Appliance | Running W | Starting W |
|---|---|---|
| 1 | 600–1,200 | 1,800–3,600 |
| 2 | 1,500–2,000 | 4,500–6,000 |
| 3 | 3,500–5,000 | 7,000–10,000 |
| 4 | 1,000–1,500 | 2,000–3,000 |
| 5 | 300–800 | 900–2,400 |
Real-world generator selection.
Total load: 10,000 W at PF 0.80:
10,000 ÷ (0.80 × 1000) = 12.5 kVA → Get 15 kVA
Total load: 30,000 W at PF 0.80:
30,000 ÷ (0.80 × 1000) = 37.5 kVA → Get 50 kVA
Total load: 50,000 W at PF 0.85:
50,000 ÷ (0.85 × 1000) = 58.8 kVA → Get 75 kVA
25 free conversion tools — each with its own unique calculator, interactive visuals, and detailed explanations.
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Common questions about generator sizing.
Add all running watts + largest starting surge. Divide by PF × 1000. Add 25% margin.
Standby: 0.80. Prime/continuous: 0.85. Check manufacturer specs.
For safety, future load growth, and to avoid running the generator at 100% capacity continuously.
Typical home needs 10–25 kVA depending on appliances. Central AC adds 5–8 kVA alone.
Not continuously. Most generators should run at 70–80% of rated capacity for longevity.