Energy Units and Measurement

A physicist measures energy in joules. An electrician measures it in kilowatt-hours. A heating contractor measures it in BTUs. A policy analyst measures it in quads. They are all measuring the same physical quantity, but four different professional traditions gave it four different names.

The joule (J) is the SI base unit: the energy needed to push with one newton of force over one meter. It is tiny by everyday standards. Lifting an apple one meter takes about 1 joule. A watt is one joule per second, so a kilowatt-hour (kWh) is the energy delivered by one kilowatt running for one hour: 3,600,000 joules (3.6 MJ). This is the unit on your electricity bill.

The British thermal unit (BTU) is the energy needed to raise one pound of water by one degree Fahrenheit: about 1,055 joules. BTUs dominate U.S. heating and natural gas markets. The quad (quadrillion BTU, 10¹⁵ BTU) measures national-scale energy: the U.S. uses about 94 quads per year.

Key conversions to memorize: 1 kWh = 3,412 BTU. 1 kWh = 3.6 MJ. These two relationships let you move between the most common energy units in any policy document.

Worked Example

A natural gas plant generates 1,000 MWh of electricity. You need to report this in BTUs for a government filing.

• Convert MWh to kWh. 1,000 MWh = 1,000,000 kWh.
• Convert kWh to BTU. 1,000,000 x 3,412 = 3.412 x 10⁹ BTU = 3.412 billion BTU.

How would you express this in therms (1 therm = 100,000 BTU)?

3,412,000,000 / 100,000 = 34,120 therms. Knowing two conversion factors (kWh to BTU and BTU to therms) handles most practical needs.

The next time a headline mixes kWh, BTUs, and quads in the same paragraph, the conversion factors above are the only tool needed to catch the error, or confirm there isn't one.

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