Ampere to watt calculation

In this tutorial we will learn that how to do ampere to watt calculation in a very simple way. By the end of this post, you will learn that, 1 ampere will be equal to how many watts?

Electrical appliances are rated in terms of electric power(watts), and the power of an electric appliance is the rate at which electrical energy is converted into other form of energy.

Unit of electric power(P) is watt(W), and if have the voltage(V) and current(A) values already given, then we can easily calculate the power in watts.

We have three types of situations for ampere to watt calculation as follows:

  1. DC
  2. Single phase AC
  3. Three phase AC

We will discuss all three cases separately for better understanding of ampere to watt calculation.

Power calculation for DC

It is very simple to calculate the power in watts for this case. To Calculate the power, we just have to multiply the voltage and current values.


Where,   P= power in watts

               V= voltage in volts

               I= current in ampere

For example, let, Voltage= 12 V

                            Current= 1 A

Then, P = V*I

So,  P = 12 * 1 = 12W

Single phase AC power calculation

In this case, the voltage and current multiplication is there but one more thing is extra which is cosɸ and we call it as power factor.


Power factor is basically the measure of How efficiently the incoming power is being utilised in your electrical system. Total incoming power (Apparent power) has basically two parts, active and reactive power. To know more about power factor in detail in this post click here.

We have 3 types of loads as Resistive, Inductive and Capacitive. The value of Power factor ranging from 0 to 1 for different types of loads.

For purely resistive load the value of power factor is 1. It means that value of cosɸ will be equal to 1. So, power calculation will be like this:

Example: Voltage=230V, Current=2A, cosɸ=1


                                    P= 230*2*1

                                     P= 460 Watts.

For inductive and capacitive loads in households, the optimum value for factor is around 0.8

For example,





P=V*I* cosɸ

P= 230*2*0.8

P=368 W.

In this way we can calculate the power for single phase AC supply.

Power calculation for Three phase AC

The power calculation for three phase AC system can be done in two ways,

  1. When Phase values are given then power will be calculated as three times of single-phase power as shown below,

Total power = 3*power per phase

       P=3*Vph*Iph* cosɸ

  1. When line current and line voltage is given the power will be calculated as,

       P=√3 *VL*IL* cosɸ

If you are unaware that what is line current, phase current and line voltage, phase voltage are then, you can Click here to read.

Generally, in three phase AC system, the line voltage and line current values are given, so you can directly use the formula provided in second case. P=√3 *VL*IL* cosɸ


VL = 415V

IL = 1A

cosɸ = 0.85


P=√3 *VL*IL* cosɸ

P=  √3 * 415*1*0.85

P= 611 W

This is how we can do the ampere to watt calculation for all three cases.

You can also read more such topics here,

Why power is generated and transmitted in 3 phases only?

What is power factor?

Why Earth pin is longer and thicker in a 3-pin plug?