An Equivalence You Should Know

The energy in 1 gallon of gasoline is 31,500 food calories.

(This should be common knowledge.)

Calculate it yourself.


Corn is being used to produce ethanol to add to gasoline in order to reduce the demand for oil which is a non-renewable energy source while corn and the ethanol made from it are renewable. (This process also recycles the carbon from air to corn to air, rather than taking carbon stored in oil and adding it to air.)

This is Spring 2008 and the price of corn has recently greatly increased due in part to its use in the production of ethanol. As a result, farmers have switched some production from other crops such as wheat to corn and the price of wheat has now increased. Also, corn is the energy source for much of our meat so the price of meats and eggs has increased this past year.

Basically the process is taking a food (corn) and transforming it to a gasoline alternative to run our automobiles and trucks. (Other organic materials besides corn are being considered to do this as well, but here we consider the practicality of using corn.)

When we consider this process, we should ask how many food calories are there in a gallon of gasoline. Is it practical to convert a food to a gasoline replacement? 

Note: Converting corn to food and converting corn to ethanol have efficiencies of less than 100%. Those efficiencies are part of the comparison as well, but depend on the methods and foods we compare. If the efficiencies are the same, the relative energy comparison is unchanged.


Here is how you can calculate this.

To start we need to know how much energy is in a gallon of gas. You can find this at: .      (We are using a government web site as reference here.)

Answer: One gallon of gasoline has 125,000 Btu of energy. (Btu = British thermal unit and is a measure of energy.)

Now we need to know how many calories in a Btu. (Caution. At this point you also need to know that there are two units called calories. A calorie is defined as the energy required to raise 1 gram of water 1 degree C. This is also called a gram calorie and is the calorie unit most used in science. A kilogram calorie (or kilocalorie) is the energy required to raise a kilogram of water 1 degree C. This is the unit used on food labels. Here we call it a food calorie and it equals 1000 calories.)

To convert Btu's to calories we can go to:
to get the number of calories in 1 Btu.      (We are again using a government web site as reference here.)

Answer: One Btu equals 0.000252 million calories which is 0.252 kilocalories.

Therefore, one gallon of gasoline has (125,000 Btu) x (0.252 kilocalories/Btu) = 31,500 kilocalories (food calories)

1 gallon of gasoline = 31,500 food calories

Since adults typically need 2000 to 2500 food calories per day, this means that (at equal efficiencies) in order to replace one gallon of gasoline with corn based ethanol, we must give up about two weeks (12 to 16 days) of food!

Is there enough farm land to do this? And, how will it effect food prices and the environment?

Revised - 8Nov2015. (New link for energy in gasoline)