In 1776, one book, written in complex language, sold over 120,000 copies in Colonial America. That number does seem large on its own. However, to give it even more meaning, I like to convert it to an equivalent number today.
This conversion is a task for proportional reasoning—one of my favorite tools for finding meaning in the numbers that surround us. First convert 120,000 into a fraction of the U.S. population in 1776: compared to the population at the time of 2.5 million, 120,000 is roughly 1 in 20, or 5%. Today’s U.S. population is about 300 million—of which 5% is 15 million.
Fifteen million copies today! More surprisingly, Common Sense by Thomas Paine sold this equivalent in just three months. In its first year, it sold 500,000 copies, or 20% of the colonial population. Today’s equivalent is 60 million copies. On Wikipedia’s list of bestselling books, all books that have sold that many or more copies have done so over a much longer time. The shortest time is 8 years, for The Da Vinci Code; several others, such as Heidi, were published in the 19th century.
Another surprise arrives upon opening Common Sense: the sophistication of the writing and reasoning.