Joule (J)

Definition

The SI unit of energy, one newton-meter (one watt for one second).

History

The joule is the SI unit of energy, named after James Prescott Joule, who showed in the 1840s that heat and mechanical work are equivalent. It is the work done by one newton acting over one meter.

Where it is used

Joules are the standard energy unit in physics and appear on appliance and equipment ratings.

Typical uses include physics, appliance ratings.

Conversion pages

These pages convert joule to or from another unit in energy.

• Calorie to joule
• Kilowatt-hour to joule
• British thermal unit to joule

Other Energy units

• Kilocalorie (kcal)
• Kilojoule (kJ)
• Calorie (cal)
• Kilowatt-hour (kWh)
• British thermal unit (BTU)
• Watt-hour (Wh)

Sources

• NIST SP 811 NIST SP 811, Appendix B; ISO 80000-5 (energy) · Dataset reviewed Nov 11, 2026