This calculator helps you convert electrical current (Amperes, A) and voltage (Volts, V) into real power (Kilowatts, kW). This is a fundamental calculation in electrical engineering and is crucial for sizing equipment, understanding energy consumption, and ensuring electrical system safety.
The Formulas
The calculation differs slightly depending on whether you are dealing with Direct Current (DC) or Alternating Current (AC) circuits, and for AC, whether it's single-phase or three-phase.
1. Direct Current (DC) Circuits:
In DC circuits, the relationship is straightforward:
Power (Watts) = Voltage (Volts) × Amperage (Amperes)
P (W) = V × I
To convert Watts to Kilowatts, divide by 1000:
Power (kW) = (Voltage × Amperage) / 1000
2. Alternating Current (AC) Circuits:
AC circuits introduce the concept of Power Factor (PF), which accounts for the phase difference between voltage and current. This difference arises from inductive or capacitive loads (like motors or fluorescent lights) and affects the real power consumed.
a) Single-Phase AC:
The formula for real power in single-phase AC circuits is:
Power (Watts) = Voltage (Volts) × Amperage (Amperes) × Power Factor
P (W) = V × I × PF
To convert to Kilowatts:
Power (kW) = (Voltage × Amperage × Power Factor) / 1000
b) Three-Phase AC:
Three-phase systems are more efficient and common in industrial and commercial settings. The formula accounts for the square root of 3 (approximately 1.732):
Power (Watts) = √3 × Voltage (Volts) × Amperage (Amperes) × Power Factor
P (W) = √3 × V × I × PF
To convert to Kilowatts:
Power (kW) = (√3 × Voltage × Amperage × Power Factor) / 1000
How This Calculator Works
This calculator takes your inputs for Voltage, Amperage, Power Factor, and Phase type.
It assumes a Power Factor of 1 for DC circuits (as PF is not applicable).
For AC circuits, it uses the provided Power Factor. A PF of 0.9 is a common estimate for many motor loads. A PF of 1.0 is ideal but rarely achieved in practice with inductive loads.
It applies the correct formula based on your selection of Single-Phase or Three-Phase AC.
The final result is displayed in Kilowatts (kW).
Use Cases
Electrical Panel Sizing: Determine the total load in kW that a panel can handle or is currently drawing.
Equipment Load Calculation: Estimate the power requirements for motors, machinery, or an entire facility.
Energy Audits: Understand the real power consumption of different circuits or appliances.
Generator Sizing: Calculate the appropriate generator capacity needed to power a load.
Inverter Sizing: Determine the kW rating required for inverters in solar or backup power systems.
Example Calculation
Let's say you have a three-phase AC system with:
Voltage: 480 V
Amperage: 100 A
Power Factor: 0.85
Using the formula for three-phase AC:
kW = (√3 × 480 V × 100 A × 0.85) / 1000
kW = (1.732 × 480 × 100 × 0.85) / 1000
kW = (70550.4) / 1000
kW ≈ 70.55 kW
If you were calculating for a single-phase AC system with the same voltage and amperage (and PF 0.85):
kW = (480 V × 100 A × 0.85) / 1000
kW = (40800) / 1000
kW = 40.8 kW
This highlights the significant difference in apparent power handling between single-phase and three-phase systems for the same voltage and current.
function calculateKilowatts() {
var voltage = parseFloat(document.getElementById("voltage").value);
var amperage = parseFloat(document.getElementById("amperage").value);
var powerFactor = parseFloat(document.getElementById("powerFactor").value);
var phase = document.getElementById("phase").value;
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = "; // Clear previous result
if (isNaN(voltage) || isNaN(amperage) || isNaN(powerFactor)) {
resultDiv.innerHTML = 'Please enter valid numbers for Voltage, Amperage, and Power Factor.';
return;
}
if (voltage <= 0 || amperage <= 0 || powerFactor 1) {
resultDiv.innerHTML = 'Inputs must be positive, and Power Factor must be between 0 and 1.';
return;
}
var kilowatts = 0;
var watts = 0;
if (phase === "single") {
// Single-phase AC or DC (assuming PF=1 for DC conceptually here if not specified)
// The calculator handles PF input, so we use it for single-phase AC.
// For DC, PF is implicitly 1, but we still use the single-phase formula structure.
watts = voltage * amperage * powerFactor;
} else if (phase === "three") {
// Three-phase AC
var sqrt3 = Math.sqrt(3);
watts = sqrt3 * voltage * amperage * powerFactor;
}
kilowatts = watts / 1000;
resultDiv.innerHTML = 'Calculated Power: ' + kilowatts.toFixed(2) + ' kW';
}