How did the Romans write numbers?
๐ In short
On some old clocks and for book chapter numbers we see letters instead of digits: I, V and X. These are Roman numerals, used by the Romans two thousand years ago. They have no zero and are written with just seven letters that are added and subtracted.
๐คฉ Did you know?
- The biggest number usually written in Roman numerals is 3999: MMMCMXCIX.
- Some clocks write four as IIII instead of IV to look nicer and more balanced.
- In Roman numerals the year 2026 is written MMXXVI.
- There is no zero in Roman numerals.
๐ Find out more
๐ The seven letters
I = 1, V = 5, X = 10, L = 50, C = 100, D = 500 and M = 1000. With these letters the Romans wrote all their numbers.
๐ Adding from the left
If the smaller letter comes after the bigger one, we add them: VI = 5 + 1 = 6, XII = 10 + 1 + 1 = 12 and CL = 100 + 50 = 150.
๐ก And sometimes we subtract
If the smaller letter comes before the bigger one, we subtract it: IV = 5 โ 1 = 4, IX = 10 โ 1 = 9 and XL = 50 โ 10 = 40. That way no letter is repeated more than three times.
๐ฏ Why did we stop using them?
Calculating with Roman numerals is very hard: try multiplying XLVII by XIII! They have no zero and no place value. So the world chose Arabic numerals, and Roman ones are left for decoration and numbering chapters and centuries.
๐งฎ Worked examples
- XIV = 10 + 4 = 14X is ten and IV is four.
- XC = 100 โ 10 = 90X comes before C, so we subtract it.
- MMXXVI = 20261000 + 1000 + 10 + 10 + 5 + 1.
๐ Key words
- Roman numerals
- Latin letters the Romans used to write numbers
- Century
- A hundred years, often numbered with Roman numerals
- The Romans
- An ancient people who built a great empire with Rome as its capital
๐งช Try it at home
Write your age and then today's date in Roman numerals. Then look around the house or in books for a clock or a chapter written with them, and read it.
๐งฉ Test yourself
1 What is X in Roman numerals?
2 How is 4 usually written in Roman numerals?
3 Which number has no Roman symbol?