Roman numerals show up in more places than you'd think — movie copyright dates, Super Bowl numbers, book chapters, clock faces, and the cornerstones of old buildings. They look intimidating, but the whole system runs on just seven letters and one rule.
The seven letters
Each letter stands for a fixed value:
- I = 1
- V = 5
- X = 10
- L = 50
- C = 100
- D = 500
- M = 1000
Write them from largest to smallest and add them up. So MMXXVI is 1000 + 1000 + 10 + 10 + 5 + 1 = 2026.
The one rule that trips people up
To avoid writing four of the same letter in a row, Roman numerals use subtraction: a smaller letter placed before a larger one means “subtract it.”
- IV = 5 − 1 = 4 (not IIII)
- IX = 10 − 1 = 9
- XL = 50 − 10 = 40
- XC = 100 − 10 = 90
- CD = 400, CM = 900
That's why 2024 is MMXXIV and 49 is XLIX. Once the subtraction pairs click, reading any numeral is just adding and subtracting as you scan left to right.
Why it stops at 3999
Standard Roman numerals only go up to 3999 (MMMCMXCIX). Beyond that you'd need more than three M's, so the Romans used a bar over a letter to multiply it by 1000 — a notation nobody uses day to day. For everyday purposes, 1 to 3999 covers it.
How to use it
Rather than decoding letter by letter, the Roman Numeral Converter goes both ways. Type a number to see it as a numeral, or paste a numeral like MCMLXXXIV to read its value — it even checks that what you entered is valid, so you'll know if a numeral is written incorrectly.
If you're curious how numbers work in other systems too, the Number Base Converter shows the same value in binary, octal, and hexadecimal — the notations computers use instead of ancient Rome's.