Room for ChanceWhat it measures and where it is used
Energy measures the capacity to do work or transfer heat. The joule connects mechanical and thermal descriptions associated historically with James Prescott Joule. Kilowatt-hours measure energy, not power. The thermochemical calorie is 4.184 J; the BTU shown uses the International Table convention.
- Classification
- SI derived quantity
- SI unit
- J = kg·m²·s⁻²
- Dimension
- M L² T⁻²
L: length; M: mass; T: time; Θ: temperature; N: amount of substance. The dimension symbol N is not the unit symbol for newton.
How it works
The calculation first converts to a common reference unit, then to the destination unit. Factors in the table show the reference value for one unit.
Example
1 kWh ≈ 3,600,000 J
Available units
Reference unit: J
| Available units | Reference factor |
|---|---|
| J | 1 × x |
| kJ | 1,000 × x |
| MJ | 1,000,000 × x |
| Wh | 3,600 × x |
| kWh | 3,600,000 × x |
| cal (th) | 4.184 × x |
| kcal (th) | 4,184 × x |
| BTU (IT) | 1,055.05585262 × x |
| eV | 0.0000000000000000001602176634 × x |
Units, history and conventions
The International System of Units (SI) received its name in 1960. Since the 2019 revision, its definitions use fixed values of seven defining constants. SI base and derived quantities should not be confused with the different units used to express them.
IUPAC does not replace the SI: its Green Book standardises quantities, symbols and terminology in physical chemistry. Its predecessor was published in 1969. The mole is particularly important when counting specified chemical entities.