# Energy Units

## Units

The first step in understanding the energy problem is understanding the numbers; the following gives an overview of the major energy units used in various different reports on energy use. If you're not sure what a 'quad' is, or how it compares to a TW or a billion bboe, read on!

The metric unit for energy is the joule (1J).
For power, or energy use per unit time, the unit is the watt (1W).
The metric time unit is the second (1 s) so

1 J = 1 W * 1 s

It also helps to be familiar with the standard metric prefixes for large numbers, since we'll be dealing with some very large numbers here. Each of these is 1000 times larger than the previous:
prefix
symbol
nameamount
kkilo-1000
Mmega-1 million
Ggiga-10^9 (1 billion)
Ttera-10^12 (1 trillion)
Eexa-10^18
Zzetta-10^21

Many other energy and time units are frequently used in reporting energy industry data:
Unit name equivalent to
1 BtuBritish thermal unit1055 J
1 kWhkilowatt-hour3.6 MJ (megajoule)
1 kWhkilowatt-hour3412 Btu
1 bboebarrel of oil equivalent5.8 million Btu
1 bboebarrel of oil equivalent6.12 GJ (gigajoule)
1 bboebarrel of oil equivalent1700 kWh
1 toe(metric) ton of oil equivalent39.7 million Btu
1 toe(metric) ton of oil equivalent41.9 GJ
1 tce(metric) ton of coal equivalent27.8 million Btu
1 tce(metric) ton of coal equivalent29.3 GJ
1 short ton coal2000 lb of coal equivalent25 million Btu
Note that coal has only about 70% the energy content of oil, for the same weight.
The following units are on the scale of yearly world energy consumption (1 year = 8766 hours or 31.5 million seconds):
1 TWhterawatt-hour1 billion kWh
1 TWyterawatt-year8766 TWh
1 TWyterawatt-year31.5 EJ (exajoule)