The kilowatt‑hour (\(\text{kWh}\)) is a unit of energy commonly used to measure electrical consumption. It represents the amount of work done when a power of one kilowatt is applied for one hour. In SI terms, \(1\,\text{kWh}=3.6\times10^{6}\,\text{J}=3600\,\text{kJ}\).
Understanding Kilojoule (kJ)
The kilojoule (\(\text{kJ}\)) is a metric unit of energy equal to one thousand joules. It is widely used in scientific calculations, nutrition labeling, and engineering analyses where smaller energy quantities are involved.
Practical Applications
Electric utilities bill customers in kWh.
Thermal‑energy calculations for heating, cooling, and process engineering often use kJ.
Battery capacity, solar‑panel output, and electric‑vehicle range are expressed in kWh, then converted to kJ for detailed energy‑balance studies.
Conversion Relationship
Because 1 kW = 1000 W and 1 h = 3600 s, the conversion factor between kWh and kJ is exactly 3600.0:
\(1\,\text{kWh}=3600\,\text{kJ}\)
Kilowatt-hour to Kilojoule Conversion Reference Table
Kilowatt-hour (kWh)
Kilojoule (kJ)
0.1
360
0.5
1800
1.0
3600
2.0
7200
5.0
18000
10.0
36000
20.0
72000
50.0
180000
100.0
360000
500.0
1.8000e+06
1000.0
3.6000e+06
Step‑by‑Step Conversion Example
Convert 10 kWh to kilojoules.
Identify the conversion factor: \(1\,\text{kWh}=3600\,\text{kJ}\).
The factor comes from the definition of the hour (3600 seconds) and the kilowatt (1000 watts). Energy = power × time, so 1 kW·h = 1000 W × 3600 s = 3 600 000 J = 3600 kJ.
Use kWh when dealing with electrical energy billing, large‑scale power systems, or any context where energy is measured over hours. Use kJ for thermodynamic work, heat transfer, or when the energy quantities are smaller or need to be integrated with other SI units.
"On fait la science avec des faits, comme on fait une maison avec des pierres ; mais une accumulation de faits n'est pas plus une science qu'un tas de pierres n'est une maison." "Science is built up of facts, as a house is built of stones; but an accumulation of facts is no more a science than a heap of stones is a house." — Henri Poincaré (French Mathematician, Theoretical Physicist & Mining Engineer)