Joules to Watts Calculator

To convert joules to watts, divide the energy in joules by the time in seconds. The result is the average power over that time. Because a watt is one joule per second, the same energy delivered faster means more watts.

Joules to watts formula

Worked examples

• Boiling water: heating 1 litre of water from 20 °C to 100 °C needs about 4,186 J/kg·°C × 1 kg × 80 °C = 334,880 J. To do it in 3 minutes (180 s) needs 1,860 W of heat, so a kettle of about 2 kW, allowing for some losses.
• Lifting a load: raising 100 kg by 2 m takes m × g × h = 100 × 9.81 × 2 = 1,962 J. Doing it in 2 seconds needs 981 W.
• Battery runtime check: 360,000 J used in one hour (3,600 s) is an average of 100 W.

Joules to watts table

The units behind the formula

• Joule (J): the SI unit of energy. 1 J = 1 watt for 1 second = 1 volt × 1 coulomb.
• Volt (V): electric potential difference, defined as 1 joule of energy per coulomb of charge.
• Coulomb (C): electric charge. One coulomb is the charge carried by a current of 1 ampere in 1 second, about 6.242 × 10¹⁸ electrons.
• Watt (W): power, the rate of energy transfer. 1 W = 1 J per second.

Average versus peak power

Dividing total energy by total time gives an average. A camera flash or defibrillator releases its stored energy in milliseconds, so its peak power is enormous even though the energy itself is modest. Dividing the same joules by a shorter time gives a much higher wattage.

Related conversions: watts to joules · kWh to kW · joules to volts