UnitConvConvert
J
Energymetricscientific

What is a joule?

The SI base unit of energy — 1 newton-metre

Definition

The joule is the SI unit of energy, work and heat. Defined as one newton-metre or one watt-second. Named after James Prescott Joule who demonstrated the mechanical equivalent of heat. Lifting a 100 g apple 1 metre requires about 1 J.

Common uses

  • Physics and engineering calculations
  • Scientific nutrition measurement (European labels)
  • Impact energy in engineering (Charpy test)

🌍 Real-world scale

Lifting a 100 g apple 1 m: ≈ 1 J. 100 kcal snack: 418,400 J. Hand grenade: ~650 kJ.

Convert from joules

9 conversions
Joule to Kilojoule1 J = 0.001 kJJoule to Megajoule1 J = 1.0000e-6 MJJoule to Kilowatt-Hour1 J = 2.7778e-7 kWhJoule to Watt-Hour1 J = 0.0002778 WhJoule to Calorie1 J = 0.239 calJoule to Kilocalorie1 J = 0.000239 kcalJoule to British Thermal Unit1 J = 0.0009478 BTUJoule to Electronvolt1 J = 6.2415e18 eVJoule to Therm1 J = 9.4782e-9 thm

Convert to joules

9 conversions
Kilojoule to Joule1 kJ = 1,000 JMegajoule to Joule1 MJ = 1,000,000 JKilowatt-Hour to Joule1 kWh = 3,600,000 JWatt-Hour to Joule1 Wh = 3,600 JCalorie to Joule1 cal = 4.184 JKilocalorie to Joule1 kcal = 4,184 JBritish Thermal Unit to Joule1 BTU = 1,055.06 JElectronvolt to Joule1 eV = 1.6022e-19 JTherm to Joule1 thm = 105,505,585.3 J

Tips

  • 1 J = 1 N·m = 1 W·s.
  • 1 kWh = 3,600,000 J (3.6 MJ).
  • For nutrition 1 kcal = 4.184 kJ.

Common mistakes

  • Confusing joule (energy) with newton (force).
  • Mixing joule with watt — watt is joule per second.
  • Using kJ when labels call for kcal on US nutrition.

FAQ about the joule

What is a joule?
The joule is the SI unit of energy, work and heat. Defined as one newton-metre or one watt-second. Named after James Prescott Joule who demonstrated the mechanical equivalent of heat. Lifting a 100 g apple 1 metre requires about 1 J.
Where is the joule used?
The joule is commonly used for: Physics and engineering calculations; Scientific nutrition measurement (European labels); Impact energy in engineering (Charpy test).
What is an example of a joule in real life?
Lifting a 100 g apple 1 m: ≈ 1 J. 100 kcal snack: 418,400 J. Hand grenade: ~650 kJ.
What category does the joule belong to?
The joule is a unit of energy, part of the 10-unit energy category on UnitConv.
How accurate are joule conversions?
All conversion factors follow NIST and BIPM international standards to 8 significant figures — the highest practical accuracy.
Explore all 10 energy units and their conversions.⚡ Energy hub →