What is a BTU?
BTU stands for British Thermal Unit, a measure of energy. One BTU is not much: it's equal to 0.25 food calories or about the amount of energy in the tip of a match. To put this in perspective, the food energy in a peanut butter and jelly sandwich is about 1250 BTU, one kwh of electricity is equivalent to 3,412 BTU, a gallon of gasoline contains about 125,000 BTU, and one short ton of coal (2000 lbs) contains about 20 million BTU.

Because a single BTU is so small, energy is usually measured in thousands or millions of BTU. For entire economies, energy is measured in quadrillion BTU, or "quads" for short. A quadrillion is equal to 10^15. In 2002, total US energy consumption was 97.4 quads.

The metric equivalent of the BTU is the Joule. One quad equals approximately 1.055 Exajoules (10^18 Joules).

How Large is a Quadrillion BTU?
It's about equal to the amount of energy in 45 million tons of coal, or 1 trillion cubic feet of natural gas, or 170 million barrels of crude oil. In 1988, total world energy consumption was about 1 quad every 26 hours.

To make this a bit less abstract, 45 million tons of coal would be a pile 10 feet thick, one mile wide and about 3.3 miles long. At 60 mph, it would take about 9 minutes to drive around the pile.

In terms of electricity, the energy content of 1 quad is equal to about 293 terawatt-hours or 33 gigawatt-years. However, a typical steam-turbine power plant burning fossil fuels is only able to capture about a third of the energy in the fuel, so 1 quad of fuel actually produces about 11 gigwatt-years of electricity.

How Large is a Barrel of Oil?
A barrel of oil is 42 gallons. The standard unit is "bbl". The extra "b" comes from the early days of the oil industry when different companies used different-sized barrels. Standard Oil's barrels were 42 gallons and were painted blue.
Who Uses Energy?
Energy use is commonly broken down into four categories: (1) residential and commercial, (2) industrial, (3) electric utilities, and (4) transportation. Residential and commercial (office buildings and stores) are grouped together because energy is used the same way in both: primarily for lighting, heating and air conditioning. The industrial category includes mines and factories, which use large amounts of energy as part of producing their products. Electric utilities are separate from the industrial category because they really just transform energy from one form into another. The key characteristic of the transportation sector is that it requires energy that can be carried around easily.
US Energy Consumption
Notes and graphs on US energy consumption since World War II.
URL: https://wilcoxen.maxwell.insightworks.com/pages/135.html
Peter J Wilcoxen, The Maxwell School, Syracuse University
Revised 03/25/2009