KW to AMP Calculator

Convert kilowatts to amps for DC, single-phase, and three-phase circuits. Calculate electrical current with voltage, power factor, and efficiency inputs. Essential for circuit design and equipment sizing.

Current Formulas:

DC: I(A) = P(kW) × 1000 / V(V)

Single-Phase AC: I(A) = P(kW) × 1000 / (V(V) × PF)

Three-Phase AC: I(A) = P(kW) × 1000 / (√3 × V(V) × PF)

kW
The electrical power in kilowatts
V
System voltage (e.g., 120V, 230V, 480V)
(0-1)
Ratio of real power to apparent power (0 to 1)
%
System efficiency percentage (if known)
Electric Heater
2 kW, 240V, PF 1.0
Air Conditioner
3.5 kW, 240V, PF 0.85
3-Phase Motor
5.5 kW, 480V, PF 0.88
Water Heater
4.5 kW, 240V, PF 1.0
EV Charger
7.2 kW, 240V, PF 0.98
Industrial Load
15 kW, 480V, PF 0.92
Calculating...

Understanding Electrical Current

Electrical current (measured in amperes or amps) is the flow of electric charge through a conductor. When designing electrical systems, it's crucial to calculate the current draw of equipment to properly size wires, circuit breakers, and other components.

Key Electrical Formulas:

DC Current: I(A) = P(W) / V(V)

AC Current (Single-Phase): I(A) = P(W) / (V(V) × PF)

AC Current (Three-Phase): I(A) = P(W) / (√3 × V(V) × PF)

Power in Watts: 1 kW = 1000 W

Circuit Breaker Sizing

1

NEC 80% Rule: For continuous loads (operating 3+ hours), circuit breakers must be sized at 125% of the load current. This means a 20A breaker can only handle 16A continuous.

2

Wire Sizing: Wire gauge (AWG) must be selected based on both current and voltage drop considerations. Higher current requires thicker wires.

3

Safety Factors: Always include safety margins (typically 10-25%) for future expansion, voltage variations, and unexpected load increases.

Common Electrical Loads & Current Draw

Appliance Typical Power Voltage Approx. Current
Incandescent Light (100W) 0.1 kW 120V 0.83 A
LED TV (55") 0.15 kW 120V 1.25 A
Refrigerator 0.15-0.4 kW 120V 1.25-3.33 A
Microwave Oven 1.0-1.5 kW 120V 8.3-12.5 A
Electric Water Heater 4.5 kW 240V 18.75 A
Central A/C (3 ton) 3.5-5.0 kW 240V 14.6-20.8 A
EV Charger (Level 2) 7.2 kW 240V 30 A
Electric Range 7-10 kW 240V 29.2-41.7 A

Wire Sizing Guide (Copper Conductors)

Wire Gauge (AWG) Ampacity (60°C) Ampacity (75°C) Max Circuit Breaker
14 AWG 15 A 20 A 15 A
12 AWG 20 A 25 A 20 A
10 AWG 30 A 35 A 30 A
8 AWG 40 A 50 A 40 A
6 AWG 55 A 65 A 60 A
4 AWG 70 A 85 A 100 A
2 AWG 95 A 115 A 125 A
1 AWG 110 A 130 A 150 A

Applications of Current Calculations

  • Circuit Design: Sizing wires, breakers, fuses, and transformers
  • Load Analysis: Determining if existing circuits can handle additional loads
  • Equipment Selection: Choosing correct circuit breakers and disconnect switches
  • Energy Audits: Analyzing current draw to identify energy savings
  • Renewable Energy: Sizing inverters and charge controllers
  • Code Compliance: Ensuring electrical installations meet NEC requirements

Calculator Features:

  • Supports DC, single-phase AC, and three-phase AC circuits
  • Includes power factor and efficiency adjustments
  • Provides circuit breaker sizing recommendations
  • Converts results to multiple units (A, kW, W, hp, BTU/hr)
  • Includes wire sizing guidelines based on current
  • Visualizes current relationships with interactive charts

Frequently Asked Questions

Circuit breakers protect wires from overheating and potential fire hazards. If a breaker is too large for the wire size, it won't trip before the wire overheats. If it's too small, it will trip unnecessarily. Proper sizing is critical for safety and code compliance.

The National Electrical Code (NEC) requires that continuous loads (operating 3+ hours) use breakers rated at 125% of the load current. For example, a 16A continuous load requires a 20A breaker (16A × 1.25 = 20A).

Power factor significantly impacts AC current calculations. For the same real power (kW), a lower power factor requires more current. For example:
  • 5 kW at 240V with PF 1.0: I = 5000 / (240 × 1.0) = 20.8A
  • 5 kW at 240V with PF 0.8: I = 5000 / (240 × 0.8) = 26.0A
That's a 25% increase in current for the same useful power! This is why power factor correction is important in industrial settings.

In three-phase systems:
  • Line Current (IL): Current measured in each of the three supply lines
  • Phase Current (IP): Current through each winding of a three-phase load
For a wye (Y) connection: IL = IP
For a delta (Δ) connection: IL = √3 × IP

Our calculator uses line current, which is what you'd measure with a clamp meter on any of the three supply conductors.

This calculator provides full load current (FLC) for continuous operation. Motor starting (inrush) current is typically 5-7 times higher than FLC and lasts only a few seconds. For motor applications:
  • Use motor nameplate FLC for continuous load calculations
  • Size wires and breakers based on FLC (with appropriate safety factors)
  • Consider motor starting current when selecting overload protection
  • Check NEC Article 430 for specific motor circuit requirements
For accurate motor calculations, use our dedicated Motor Current Calculator.

Voltage drop occurs when current flows through wire resistance. NEC recommends limiting voltage drop to 3% for branch circuits and 5% for feeder circuits. To account for voltage drop:
  1. Calculate current using this calculator
  2. Determine one-way circuit length
  3. Use voltage drop formula: VD = (2 × K × I × L) / CM
    • K = 12.9 for copper, 21.2 for aluminum
    • I = Current in amps
    • L = One-way length in feet
    • CM = Circular mils of conductor
  4. Select wire size that keeps voltage drop within limits
For detailed voltage drop calculations, use our Voltage Drop Calculator.