Amps to kW Converter — Free Online Calculator
Convert amps to kilowatts for DC, single-phase, and three-phase circuits.
How to Use This Calculator
Enter amps, voltage, and phase type.
The Formula Explained
DC: kW = A × V / 1000. Single-phase: kW = A × V × PF / 1000. Three-phase: kW = A × V × √3 × PF / 1000.
Amps to Kilowatts: The Real Power Question
Converting amps to kilowatts is one of the most common electrical calculations, but it hides a subtlety that trips up even experienced electricians: you need three variables, not two. Voltage, amps, and power factor all matter. For DC circuits and purely resistive AC loads, the calculation is simple: kW = V × A / 1000. Add any inductive load — motors, fluorescents, solenoids — and you need to multiply by power factor. For three-phase, add a factor of sqrt(3) (1.732) because the vector sum of three phases 120 degrees apart is geometrically different from three independent single phases.
The calculation direction matters too. Converting amps to kW gives real power, which is what the utility charges for and what equipment actually does. Converting amps to kVA gives apparent power, which is what transformers and wires must be sized to handle. A 100 amp service at 240V single-phase is 24 kVA of capacity — but the actual kW delivered depends on what loads are plugged in. Resistive loads use all 24 kW; heavy motor loads might only use 20 kW with 4 kVAR reactive floating around.
Worked Example: Residential 200 Amp Service Capacity
A residential 200A main panel at 240V split-phase. Apparent capacity: 200 × 240 = 48,000 VA = 48 kVA. Real power capacity at typical residential PF of 0.95: 48 × 0.95 = 45.6 kW. That is the maximum simultaneous load the service can deliver under ideal conditions.
Typical residential load mix: HVAC 4 kW, water heater 4.5 kW, electric range 6 kW peak, dryer 5 kW, lighting and outlets 3 kW average = 22.5 kW average simultaneous, well below the 45.6 kW ceiling. The ceiling matters only during diversity-load peaks — like a winter evening with HVAC running, dryer running, oven on, shower running (water heater cycling), and kitchen appliances active. Even then, the diversity factor (not all peaks happen at once) means 200A is comfortable for most homes under 3,500 sq ft.
Worked Example: Three-Phase 480V Industrial Feeder
An industrial facility has a 400A feeder at 480V three-phase. Apparent power capacity: sqrt(3) × 480 × 400 / 1000 = 332 kVA. At a typical industrial PF of 0.85 (motor-heavy load): 332 × 0.85 = 282 kW real power.
What can 282 kW run? Roughly 378 HP worth of mechanical output (282 / 0.746), minus efficiency losses of about 10%, gives about 340 HP of usable mechanical output. For a machine shop this might mean a couple of large CNC mills, several lathes, air compressors, and overhead lighting — all running simultaneously. For continuous operation at 85% PF, you would also want power factor correction to improve efficiency and avoid utility demand penalty charges.
Common Amp-to-kW Mistakes
1. Forgetting to divide by 1000. V × A gives watts, not kilowatts. Must divide by 1000. Simple mistake but embarrassing.
2. Using line-to-neutral voltage on three-phase. Three-phase formulas use line-to-line voltage. On a 480Y/277V system, use 480V not 277V. On 208Y/120V, use 208V not 120V.
3. Assuming power factor 1.0 when motors are present. Motor loads drag PF down to 0.8-0.85 typically. Ignoring this overstates real power by 15-20%.
4. Double-counting the sqrt(3) on three-phase. Some people multiply by 1.732 AND calculate each phase separately, giving 3 × sqrt(3) = 5.2x error.
5. Using nameplate HP instead of actual running kW. A motor rated 10 HP at full load draws 10 HP / efficiency = about 8.6 kW. But motors often run at partial load, drawing less. Measure actual amps under real operating conditions, not nameplate.
Quick Reference Formulas
DC: kW = V × A / 1000. No power factor, no sqrt(3).
Single-phase AC: kW = V × A × PF / 1000. PF = 1.0 for resistive loads, 0.85 typical for motor loads.
Three-phase AC: kW = sqrt(3) × V × A × PF / 1000 = 1.732 × V × A × PF / 1000. V is line-to-line voltage. This formula assumes balanced three-phase load (all three phases carrying equal current).
Inverse formulas (kW to amps): Single-phase A = kW × 1000 / (V × PF). Three-phase A = kW × 1000 / (sqrt(3) × V × PF).
For quick field estimation at common voltages: at 120V single-phase, 1 kW = 8.3 amps (resistive). At 240V single-phase, 1 kW = 4.17 amps (resistive). At 208V three-phase, 1 kW = 2.77 amps per phase (resistive). At 480V three-phase, 1 kW = 1.20 amps per phase (resistive). Multiply by 1/PF for inductive loads.
Standards for Power Calculations
IEEE 1459 defines the modern standard for power measurements including real, reactive, apparent, and distortion power under non-sinusoidal conditions. NEC Article 220 specifies load calculation methods for residential and commercial services, using watts or volt-amps depending on load type.
NEC 215.2(A)(1) requires feeders to be sized for 125% of continuous load plus 100% of non-continuous. This sizing is in amps, and the underlying load calculation considers real loads in watts but ultimately translates to current at the feeder's voltage. NEC 430 covers motors, with specific amp-based sizing using nameplate FLA rather than calculated values from HP and voltage.
Amps to kW: backing out kilowatts from a clamp-meter reading
Inverse of kW-to-amps. You measured current with a clamp meter and need to back out real power in kilowatts to compare against ratings or specs. The math is the same three-form structure (DC, single-phase, three-phase) and needs the power factor to get from apparent to real power.
The formula and what it does
For 480 V three-phase, 100 A line current at PF 0.85: kW = (1.732 x 480 x 100 x 0.85) / 1000 = 70.6 kW. The calculator handles voltage, current, phase, and PF; it returns real kW that compares to load specs.
Worked example
Scenario: Service amp meter reads 145 A on a 240 V single-phase residential service during peak draw. Find kW.
Mixed residential load, assume PF 0.95 (most loads near unity, with some motor and reactive component). kW = (240 x 145 x 0.95) / 1000 = 33.1 kW. That is a heavy peak; combination of central AC, EV charging, and a few resistive loads (water heater, dryer, oven) all running at once.
Common mistakes to avoid
undefinedFrequently asked questions
What PF should I assume for my house?
Modern residential: 0.92-0.97 average. Heavy motor or HVAC use drops to 0.85. Lots of LED lighting and electronics with cheap PSUs can drop to 0.8. When in doubt, 0.9 is a reasonable default.
Why is my utility bill in kWh, not amps?
kWh integrates real power over time. The utility meter measures actual energy delivered, not instantaneous current. Demand charges (commercial) are based on peak kW, derived from peak amps.
How do I calculate three-phase kW from line-to-line voltage?
kW = (sqrt(3) x V_LL x I_line x PF) / 1000. V_LL is line-to-line voltage (480, 208, 230). The line current is what the clamp meter reads on any one of the three phase wires.
Do I divide by 1000 or 1024?
Always 1000. Power units use SI prefixes: kilo = 1000, mega = 1,000,000. Only data storage uses 1024.
Why does my generator hit kW limit before kVA?
Because the engine has a fixed kW capacity (mechanical power). The alternator has a kVA capacity (current carrying). On a high-PF load you hit kW first; on a low-PF load (motors) you hit kVA first.
What is the relationship to demand charges?
Commercial utility bills typically include a $/kW peak-demand charge for the highest 15-minute kW average each month. Spreading load to avoid peaks saves real money even at flat per-kWh rates.