What Are Roman Numerals?

Who invented Roman numerals? (The Romans, right?) Where did the idea come from? And why do we still use them today? Keep on reading to learn all about this ancient number system.

Jason Marshall, PhD
4-minute read
Episode #139

How to Read and Write Roman Numerals

Now that we know where Roman numerals came from, let’s talk about how the Roman numeral system works. Fortunately, you only need to know a few things to become a Roman numeral expert. First, you need to memorize the 7 symbols commonly used today and the quantities they represent:

  • I = 1
  • V = 5
  • X = 10
  • L = 50
  • C = 100
  • D = 500
  • M = 1,000

Second, you need to know that just like in the Egyptian hieroglyphic system, numbers are written by combining symbols together. For example, the number 3 is written “III” (since that’s 1+1+1), the number 7 is written “VII” (since that’s 5+1+1), the number 61 is written “LXI” (since that’s 50+10+1), and so on. The last thing you need to know is that if a smaller value is written before a larger value—something like “IV” where the symbol for 1 is written before the symbol for 5—that means that the smaller value should be subtracted from the larger value. So “IV” represents 5 – 1 = 4 and “IX” represents 10 – 1 = 9.

While those are all the rules you need to know to read Roman numerals, there are some things that can trip you up when writing them. For example, should the number 1999 be written MCMXCIX? Or can it be written much more simply as MIM instead? If you think about it, you’ll see that given the set of rules we’ve learned, these are indeed both perfectly valid ways of writing 1999. So which is right? Well, I’m not sure if one is more correct than the other, but I am sure that the first way has become the standard way of doing things.


About the Author

Jason Marshall, PhD

Jason Marshall is the author of The Math Dude's Quick and Dirty Guide to Algebra. He provides clear explanations of math terms and principles, and his simple tricks for solving basic algebra problems will have even the most math-phobic person looking forward to working out whatever math problem comes their way.