How to teach Roman numerals

Grade 3 to Grade 6

Roman numerals write numbers with seven letters, I, V, X, L, C, D and M. The rule is simple: symbols are written largest to smallest and added, unless a smaller symbol sits just before a bigger one, in which case it is subtracted. Students meet Roman numerals on clock faces, book chapters, monarch names and dates.

How to teach it

1. Start with the seven symbols and their values: I=1, V=5, X=10, L=50, C=100, D=500, M=1000.
2. Teach the addition rule first, symbols written largest to smallest are added (VIII = 5 + 1 + 1 + 1 = 8).
3. Then the six subtractive pairs (IV=4, IX=9, XL=40, XC=90, CD=400, CM=900), a smaller symbol before a larger one is subtracted.
4. Practise both directions, number to numeral and numeral to number, and read a real analog clock face together.

Common mistakes

• Writing a symbol four times in a row (IIII for 4 instead of IV).
• Subtracting the wrong symbol, only I, X and C are ever used to subtract.
• Reading IX as 11 instead of 9, the order decides add or subtract.
• Forgetting there is no zero in Roman numerals.