Roman numerals

The Romans used letters for numbers: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000. Letters are usually added, but a smaller letter before a bigger one is taken away.

Key facts

  • I 1, V 5, X 10, L 50, C 100, D 500, M 1000.
  • Add when letters go from big to small: XVI = 10 + 5 + 1 = 16.
  • Subtract when a smaller letter comes first: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900.
  • Never use more than three of the same letter in a row.

Worked examples

Example 1

What number is XLVII?

  1. XL = 50 − 10 = 40
  2. VII = 5 + 1 + 1 = 7
  3. 40 + 7 = 47

Answer: 47

Example 2

Write 2024 in Roman numerals.

  1. 2000 = MM, 0 hundreds, 20 = XX, 4 = IV.
  2. MMXXIV

Answer: MMXXIV