Generator Sizing Calculator (kW to Amps)
Convert your power load in kW to amps and find the right generator size
How to Use This Calculator
- Enter the total load you need to power in kilowatts (kW). Add up appliance wattages and divide by 1000.
- Select your voltage and whether the service is single-phase or three-phase.
- Choose a power factor (use 1.0 for resistive loads like heaters, 0.8 for motors and mixed loads).
- Pick a surge allowance if you have motor-driven equipment (AC compressors, pumps) that need extra starting power.
- The calculator shows load amps and the recommended generator size including a safety margin.
kW to Amps Formula
Single-Phase: Amps = (kW × 1000) ÷ (Voltage × Power Factor)
Three-Phase: Amps = (kW × 1000) ÷ (Voltage × Power Factor × √3)
Recommended Generator (kW) = Load kW × Surge Allowance
kVA = Recommended kW ÷ Power Factor
| Load (kW) | Amps @ 240V 1φ | Recommended Gen (25% margin) | Typical Use |
|---|---|---|---|
| 5 kW | 20.8 A | 6.25 kW | Essentials / RV |
| 10 kW | 41.7 A | 12.5 kW | Whole home (small) |
| 15 kW | 62.5 A | 18.75 kW | Whole home (medium) |
| 22 kW | 91.7 A | 27.5 kW | Large home / AC |
| 30 kW | 125 A | 37.5 kW | Large home / small biz |
Generators & Transfer Switches
Frequently Asked Questions
Why add a 25% safety margin?
Generators should run at 70–80% of rated load for efficiency and longevity. Motors like AC compressors draw 2–3× their running watts for a few seconds at startup, so a margin prevents nuisance tripping.
Should I choose single- or three-phase?
Most homes use single-phase 120/240V. Three-phase (208V or 480V) is common in commercial buildings and large equipment. Check your service panel or ask an electrician.
What size generator do I need for a whole house?
A typical 2,000 sq ft home with central AC needs about 18–22 kW. Use the calculator with your actual appliance loads for a precise figure.