Amps to kW Calculator
Convert amps to kilowatts (kW) instantly. Enter current, voltage, and power factor to calculate real power for any electrical system.
Formula & How It Works
Single Phase: kW = (Amps × Volts × PF) / 1000
Three Phase: kW = (√3 × Amps × Volts × PF) / 1000
Multiply current by voltage to get apparent power (VA), then divide by 1000 for kVA. Multiply by the power factor to get real power in kW. Resistive loads (heaters) have PF = 1.0, while motors typically have PF = 0.8-0.9. The difference between kW and kVA is the reactive power consumed by inductive loads.
Amps to kW Conversion Table
Three-phase, 240V, PF = 0.9:
| Amps | 120V (1-phase) | 240V (1-phase) | 240V (3-phase) | 480V (3-phase) |
|---|---|---|---|---|
| 5 A | 0.54 kW | 1.08 kW | 1.87 kW | 3.74 kW |
| 10 A | 1.08 kW | 2.16 kW | 3.74 kW | 7.48 kW |
| 15 A | 1.62 kW | 3.24 kW | 5.61 kW | 11.22 kW |
| 20 A | 2.16 kW | 4.32 kW | 7.48 kW | 14.96 kW |
| 30 A | 3.24 kW | 6.48 kW | 11.22 kW | 22.45 kW |
| 50 A | 5.40 kW | 10.80 kW | 18.70 kW | 37.41 kW |
| 100 A | 10.80 kW | 21.60 kW | 37.41 kW | 74.82 kW |
| 200 A | 21.60 kW | 43.20 kW | 74.82 kW | 149.65 kW |
Common Amps to kW Applications
- Generator sizing: Convert motor amp draw to kW to size generators
- Solar inverter output: Calculate kW from rated output amps
- EV charging: 30A at 240V = 7.2 kW (typical Level 2 charger)
- Breaker sizing: Verify that total load kW stays within circuit capacity
- Energy cost: Multiply kW by hours and rate ($/kWh) for operating cost
- Battery sizing: Calculate kW draw from inverter amps for battery autonomy
Frequently Asked Questions
How do I convert amps to kW?
For single phase: kW = (Amps × Volts × Power Factor) / 1000. For three phase: kW = (1.732 × Amps × Volts × Power Factor) / 1000. For example, 30A at 240V three-phase with PF 0.9 = (1.732 × 30 × 240 × 0.9) / 1000 = 11.22 kW.
How many kW is 30 amps at 240V?
At 240V single-phase with PF = 0.9: (30 × 240 × 0.9) / 1000 = 6.48 kW. At 240V three-phase: (1.732 × 30 × 240 × 0.9) / 1000 = 11.22 kW. For resistive loads (PF = 1.0), single-phase gives 7.2 kW, which is the rating of a common Level 2 EV charger.
What is the difference between kW and kVA?
kW (kilowatts) is real power that does useful work. kVA (kilovolt-amps) is apparent power, the total power delivered. The ratio kW/kVA is the power factor. For a motor drawing 10 kVA at PF 0.8, only 8 kW does real work while 2 kVA is reactive power. Generators are rated in kVA; loads are measured in kW.
How many kW is 100 amps at 240V?
At 240V single-phase with PF = 0.9: (100 × 240 × 0.9) / 1000 = 21.6 kW. At 240V three-phase: (1.732 × 100 × 240 × 0.9) / 1000 = 37.4 kW. This is the approximate capacity of a 100-amp residential service.
How do I calculate the cost of running a kW load?
Multiply kW by hours of operation and your electricity rate. For example, a 5 kW load running 8 hours at $0.15/kWh costs 5 × 8 × 0.15 = $6.00 per day. Use the amps-to-kW conversion to find the kW, then multiply by daily hours and your utility rate.
Motor Sizing Guide
Electric motors are inductive loads with power factors typically between 0.8 and 0.9. They also require significantly more current during startup (inrush) than during running. When sizing circuits and generators for motors, you must account for both running and starting current.
NEC Motor Full-Load Current (FLC) Table — 3-Phase AC Motors
NEC Table 430.250 provides full-load current values for 3-phase AC motors. Use these values for conductor sizing, breaker selection, and generator sizing:
| HP | 208V | 230V | 460V | 575V | kW (approx) |
|---|---|---|---|---|---|
| 1/2 | 2.1A | 1.8A | 0.9A | 0.7A | 0.37 kW |
| 1 | 3.5A | 3.2A | 1.6A | 1.3A | 0.75 kW |
| 2 | 6.6A | 6.0A | 3.0A | 2.4A | 1.5 kW |
| 5 | 15.2A | 13.8A | 6.9A | 5.5A | 3.7 kW |
| 10 | 28.0A | 25.0A | 12.5A | 10.0A | 7.5 kW |
| 20 | 54.0A | 49.0A | 24.5A | 20.0A | 15 kW |
| 50 | 130A | 118A | 59A | 47A | 37 kW |
| 100 | 241A | 218A | 109A | 87A | 75 kW |
Source: NEC Table 430.250. Values are for typical 3-phase squirrel-cage induction motors. Always verify with motor nameplate data.
Motor Starting Current (Inrush)
| Motor Type | Starting Current | Running Current | Ratio |
|---|---|---|---|
| Standard (DOL start) | 6× FLC | 1× FLC | 6:1 |
| Star-Delta starter | 2× FLC | 1× FLC | 2:1 |
| Soft starter | 3× FLC | 1× FLC | 3:1 |
| VFD (Variable Frequency) | 1.5× FLC | 1× FLC | 1.5:1 |
Motor circuit sizing (NEC 430.52): Breaker = FLC × 250% (inverse time breaker), Wire = FLC × 125%. For example, a 10 HP motor at 230V has FLC = 25A. Breaker = 25 × 2.5 = 62.5A (use 60A). Wire = 25 × 1.25 = 31.25A (use 10 AWG copper at 75°C = 35A).
Generator Sizing Guide
Generators are rated in kW (real power) and kVA (apparent power). When sizing a generator for motor loads, you must account for the starting surge. Use these guidelines:
Generator Sizing Steps
- Calculate total running load: Add up the running kW of all loads
- Add largest motor starting surge: Multiply the largest motor's FLC by 3-6× (depending on starter type)
- Apply 80% derating: Generators should not run above 80% capacity continuously
- Check altitude derating: Reduce output by 3-5% per 1,000 ft above sea level
- Verify voltage dip: Starting surges cause voltage dips — ensure the generator can recover
Generator Sizing Example
A facility has: lighting (3 kW), HVAC (5 kW running, 15 kW starting), well pump (1.5 kW running, 9 kW starting). Total running = 9.5 kW. Starting surge = 9 kW (well pump, largest surge). Required capacity = (9.5 + 9) / 0.8 = 23 kW. Recommend a 25 kW generator.
Generator kW to kVA Conversion
| Power Factor | kW to kVA | Example |
|---|---|---|
| 1.0 (resistive) | kVA = kW | 20 kW = 20 kVA |
| 0.9 (motor loads) | kVA = kW / 0.9 | 20 kW = 22.2 kVA |
| 0.8 (heavy motor) | kVA = kW / 0.8 | 20 kW = 25 kVA |
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