Roman Numeral Converter

When to use it

Roman numerals survive in the places where a plain number would look out of place: clock faces, chapter headings, film credits, monument inscriptions, tattoo sketches and the copyright year at the end of a television programme. They also appear in older documents and on buildings, where reading them is the actual task.

This converter works in both directions, from 1 to 3999. Type a number and it produces the numeral; type a numeral and it returns the number. Anything outside that range, or any pattern that is not standard notation, is rejected instead of being silently "fixed".

How the maths works

The seven symbols are I = 1, V = 5, X = 10, L = 50, C = 100, D = 500 and M = 1,000. The tool takes the largest symbol that fits, subtracts it and repeats, including the six subtractive pairs: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400 and CM = 900. That greedy pass is exactly how standard numerals are built.

Reading works symbol by symbol, adding each value, and the tool then converts the answer back to check the round trip. If the two do not match, the numeral was not standard: IIII becomes 4 numerically but converts back as IV, so it is refused.

A worked example

Write 2026 in Roman numerals.

1. Largest symbol that fits: M, so 2026 − 1000 = 1026, and a second M leaves 26.
2. 26: X fits twice, leaving 6.
3. 6: V fits once, leaving 1, and I closes it.
4. Result: MMXXVI — 1000 + 1000 + 10 + 10 + 5 + 1.

Reference numerals

Only six subtractive pairs exist. Writing 8 as IIX, or 45 as VL, is not a stylistic choice: it is a different, non-standard number.

Common mistakes

• Writing four as IIII. Clock faces sometimes do it for symmetry, but standard notation is IV, and the tool follows the standard.
• Subtracting more than one symbol. 8 is VIII, never IIX; only one smaller symbol may precede a larger one.
• Going past 3999. There is no standard single-letter symbol for 5000 here, so the page stops at 3999.
• Mixing cases. Lowercase input is accepted and converted, but the result is always printed in capitals.

Keep exploring

• Number to Words — the same number spelled out in English words.
• Number Base Converter — numbers written in other positional systems.
• Guide: Unit Conversion Mistakes to Avoid.