Generator Power Converter
Convert generator output between watts (W), kilowatts (kW), kVA, amps (A), and horsepower (HP).
Size standby, RV, and portable generators correctly.
Convert between watts, kW, kVA, amps, and HP. Adjust voltage and power factor for your application.
Generators are spec’d in at least four different units, and they don’t all mean the same thing. A “5 kVA” generator and a “5 kW” generator are not interchangeable. Watts, kVA, amps, and horsepower each describe a different aspect of electrical output — and confusing them is how you end up with a generator that trips out the moment your fridge starts up.
The key relationships (at 60 Hz):
- Watts (W) = real power, the actual work done
- Kilowatts (kW) = 1,000 W
- VA / kVA = apparent power, voltage × current
- Power factor (PF) = real / apparent = W / VA
- Amps (A) = current = W / V (for resistive loads)
- Horsepower (HP) = 746 watts of electrical output (mechanical: 745.7 W)
The power factor problem.
If a load were purely resistive (heaters, incandescent bulbs), kW and kVA would be equal. They’re not equal for motors, transformers, and electronics — these inductive loads have a power factor below 1, typically 0.7 to 0.95.
A generator rated 5 kVA at PF 0.8 delivers only 4 kW of real power. A heat pump pulling 3.5 kW of real power may actually need a 4.4 kVA generator (3.5 / 0.8). For typical home backup loads, multiply real watts by 1.2-1.3 to get the kVA rating you actually need.
Voltage matters.
Generators in North America output 120 V or 240 V (split-phase). Europe is 230 V single-phase or 400 V three-phase. For amp calculations:
- US 120 V: A = W / 120
- US 240 V: A = W / 240
- EU 230 V: A = W / 230
- EU 400 V three-phase: A = W / (400 × √3) = W / 693
Standard generator size buckets:
| Generator class | Typical rating | Use case |
|---|---|---|
| Inverter portable | 1-2 kW | Camping, recreation, single power tool |
| Small portable | 3-5 kW | Tailgate, RV, small jobsite |
| Mid portable | 5-8 kW | Whole-home essentials, larger RV |
| Large portable | 8-12 kW | Full-load home backup |
| Standby home | 14-22 kW | Whole-home permanent backup |
| Commercial standby | 25-150 kW | Small business, light commercial |
| Industrial | 200+ kW | Manufacturing, data center |
Starting watts vs running watts.
Most generator specs list two numbers: running watts (continuous) and surge / starting watts (3-10 seconds when motors spin up). A typical refrigerator runs at 200-300 W but draws 1,200-1,800 W for the half-second the compressor kicks on. Generator sizing is dominated by the starting-watt total of your biggest motor load.
Common starting-watt multipliers (start ÷ run):
| Appliance | Start multiplier |
|---|---|
| Refrigerator / freezer | 3-5× |
| Window AC | 3-4× |
| Central AC | 3-4× |
| Well pump | 4-6× |
| Power tools (saw, drill) | 2-3× |
| Pure resistive load (heater) | 1× |
| Electronics, LED lighting | 1× |
| Microwave | 1.5-2× |
Whole-home sizing example.
A modest household running essentials during an outage:
- Refrigerator: 700 W start, 200 W run
- Freezer: 1,000 W start, 250 W run
- Furnace blower: 1,200 W start, 600 W run
- Lighting: 400 W
- Modem/router: 50 W
- TV: 150 W
- Total running: 1,650 W
- Total with biggest single start (freezer 1,000 W replacing its 250 W run): 1,650 + 750 = 2,400 W peak
A 3,500 W (running) / 4,200 W (peak) inverter generator handles this. Many generators are rated higher than needed because adding more loads later (well pump, AC) demands additional headroom.
Horsepower for engine-driven generators.
The mechanical engine driving a generator typically rates 1.5-2 HP per kW of electrical output, allowing for inefficiency. A 7 kW generator usually has a 13-16 HP engine. Don’t confuse the engine HP with the electrical HP-equivalent of the output (1 kW ≈ 1.34 HP electrical).
The 80% rule.
For continuous loads (running for more than 3 hours), use no more than 80% of the generator’s rated capacity. A 5 kW generator should run 4 kW of continuous loads. The remaining 20% is reserve for startup surges and to avoid heat-soaking the alternator.
Standby vs prime power ratings.
Commercial generators carry two ratings:
- Prime power: continuous use, no time limit
- Standby: emergency use only, typically up to 200 hours per year
Standby rating is 10-15% higher than prime rating for the same physical generator. A standby-rated 22 kW generator should not run 24/7 — you’d burn out the alternator within months.
Fuel and runtime.
Generator runtime depends on tank size and load. A typical 5 kW gasoline generator with a 4-gallon tank at 50% load runs about 8 hours. Propane generators offer cleaner emissions and longer fuel storage life but typically deliver 10-15% less power than the same engine on gasoline.
Selecting from these numbers.
For most home backup: pick a generator with a running-watt rating that exceeds your total continuous load by 25%, and a surge-watt rating that exceeds your biggest motor’s startup demand. Don’t try to be precise — generators that operate near 100% capacity wear out fast and fail when an unexpected load shows up.