Roman Numerals: How to Read, Write, and Convert Them

Roman numerals are still everywhere: century numbers, chapter headings, clock faces, volume numbers, and copyright years in movie credits. But reading a long string like MCMXCIV at a glance isn't easy. Let's walk through the rules.

The basic symbols

How they combine

The core rule is addition and subtraction between neighboring symbols:

• If a smaller symbol comes after a larger one, the values add up: VI = 5 + 1 = 6.
• If a smaller symbol comes before a larger one, it's subtracted: IV = 5 − 1 = 4, IX = 10 − 1 = 9.

Subtraction only happens in specific pairs: IV (4), IX (9), XL (40), XC (90), CD (400), CM (900). You can't write 4 as IIII (except on some clock faces).

Examples

• XII = 12
• XIX = 19
• XXI = 21 (as in the 21st century)
• MCMXCIV = 1000 + 900 + 90 + 4 = 1994
• MMXXVI = 2026

Centuries and years

A century's number is written in Roman numerals: the 19th century is XIX, the 21st is XXI. To find the century from a year, divide the year by 100 and round up: 1994 falls in the 20th century (XX), while 2026 falls in the 21st (XXI).

Converting online

Rather than counting by hand, especially for large numbers and years, use the Roman numerals tool: it converts both ways — numbers to Roman numerals and Roman numerals back to numbers. Everything runs locally in your browser.

A related task

If you need to spell out a number in words instead of Roman numerals (for example, writing an amount out in full for a document), that's a different tool — the number-to-words converter.