# Watt Calculator

Welcome to our **watt calculator**, where you can calculate the *electrical power* using the **Watt's law** and Ohm's law. If you're curious about the relation between *power, voltage, current*, and *resistance*, or you're wondering how to calculate watts, you've come to the right place! Keep reading to learn the basics of electrical power, including calculating watts using the watts formula.

## Electric power and Watt's law: Calculating watts from volts and amps

Electric power is the **rate of electric energy** carried in a circuit. Devices like electric generators produce electric power, while appliances (loads) like electric motors and light bulbs *consume* it to produce *light, heat, or mechanical work*.

**Watt's law** connects electric power to the *voltage* and *current* in a circuit:

Where:

- $P$ - Electric power;
- $V$ -
**Voltage**, the electric potential difference between the two ends of a circuit; and - $I$ -
**Current**, the rate of flow of electric charge through the circuit.

The SI unit of power is **Watt** $(\text{W})$, voltage is **volts** $(\text{V})$, and current is **amperes** or amps $(\text{A})$. Thus the power calculation involves calculating watts from volts and amps using the watts formula.

The term *wattage* refers to power measured in watts. One watt $(1\text{ W})$is the electric power transferred by a voltage of one volt $(1 \text{ V})$ through the flow of one-ampere $(1 \text{ A})$ current.

## Ohm's law and electric power

Ohm's law established a relationship between the voltage and current in a circuit by stating that they're directly proportional to each other:

Where $R$, the proportionality constant, is the **resistance** to the flow of current in a circuit. We measure resistance in **ohms** $(\Omega)$.

Combining this relation to Watt's equation, we get two new equations for electric power:

Now you can find power from:

- Voltage and current using Watt's law;
- Voltage and resistance by combining Watt's equation and Ohm's law; or
- Current and resistance by combining Watt's formula and Ohm's law.

To calculate power transferred through multiple resistors, head to our resistor wattage calculator.

## How to calculate watts

Let's learn how to find watts with some examples:

- A current of $0.5 \text{ A}$ passes through a light bulb. The domestic voltage supply in the USA is $120 \text{ V}$. Let's use Watt's law to find the wattage of the light bulb:

- A voltage of $220 \text{ V}$ drives current through a $100 \text{ }\Omega$ resistor. The electric power in the circuit is:

## How to find watts using this watt calculator

This watt calculator is easy to use:

- To calculate watts from volts and amps, enter the value of
*voltage*and*current*. - Enter the values of
*voltage*and*resistance*to calculate wattage from volts and ohms. - Input the
*current*and*resistance*values to find electric power from amps and ohms.

This watt calculator is versatile enough for you to enter any two of the four parameters to find the remaining values! Use it to find volts or amps from the power consumed in watts!