With the Watt Calculator, you can quickly and easily calculate the power in watts of an electrical appliance or system. To do this, enter the existing voltage in volts and the current in amperes, and the Watt Calculator will then automatically determine the corresponding wattage. The Watt Calculator is helpful, for example, to determine the power consumption of household appliances, to determine the required power of power supplies or batteries, or to calculate the optimal size of solar systems.

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Would you like to calculate the voltage in volts or the current in amperes instead of calculating the wattage, i.e., the electrical power? If so, you can use our guide pages with the Ampere Calculator or the Volt Calculator.

The topic "Calculating Watts" deals with determining how much power an electrical device or system consumes or generates. Watt is the unit of power, is abbreviated internationally as "W", and indicates how much energy is converted per unit of time. The calculation of the wattage is important, for example, to determine electricity costs, to choose the appropriate power supply, or to determine the optimal size of electrical equipment.

Wattage is often used to measure and compare the electrical power of appliances and equipment. Watt is the unit of (electrical) power in the International System of Units (SI). It is named after the Scottish engineer James Watt, who invented an improved steam engine in the 18th century and thus drove the industrial revolution. The unit Watt indicates how much energy is converted per unit of time. More precisely, one watt is equal to one joule per second, which means that a device or equipment with a power of one watt converts an energy of one joule in one second.

The power in watts is obtained by multiplying the electrical voltage in volts by the current in amperes. The formula is therefore:

Formula for watt

Watt (W) = Voltage (V) × Amperage (A)

This formula indicates how much power an electrical device or equipment converts, given the voltage and amperage. The voltage (V) is measured in volts and indicates how much electrical potential difference there is between two points, while the amperage or current (A) is measured in amperes and indicates how much electrical current flows through a component. By multiplying these two quantities, you get the power in watts that the appliance or system converts.

In the Watt Calculator, the power in watts is already preset under "What should be calculated?” According to the formula Watt (W) = Voltage (V) × Amperage (A), the Watt Calculator still needs the two remaining entries for the voltage in volts and the amperage in amperes to calculate the power in watts. These two required inputs are described below:

Voltage in volt

Please enter the electrical voltage in volts.
If you have an indication in millivolts (mV), you must first multiply this value by 1000 to convert it into volts.
The electrical voltage has the formula symbol "U" (from Latin urgere: to urge, to press).
In the international system of units, voltage is expressed in volts and has the unit symbol "V".

Amperage in ampere

Please enter the amperage in amperes.
If you have a value in milliamperes (mA), you must first multiply this value by 1000 to convert it into amperes.
The current strength has the formula symbol "I" (from the French intensité du courant).
In the international system of units, the amperage is given in the unit ampere and has the unit symbol "A".

The battery of an e-bike always has a certain output, which is calculated from its values for voltage in volts and amperage in amperes. If the battery has an output voltage of 36 volts and a current of 15 ampere-hours, the Watt Calculator will calculate: