Roman Numerals
Convert between Roman numerals and numbers up to 3,999,999,999 with vinculum overlines.
MMXXVI
2026
Standard notation (no overline) covers 1โ3999 exactly as the classical rules require.
About the Roman Numerals
Convert numbers to Roman numerals and back in both directions at once, from 1 all the way to 3,999,999,999. Numbers of 4,000 and above use vinculum notation โ an overline multiplies the symbols by 1,000 and a double overline by 1,000,000. Malformed forms like IIII or misplaced overbars are rejected through round-trip validation rather than silently producing a wrong number.
How to use the Roman Numerals
- Type any number up to 3,999,999,999 in the left field to get its Roman numeral.
- Type a Roman numeral such as MMXXVI in the right field to get the number.
- Check the red notes if an entry is rejected โ they explain the valid ranges.
- Both fields accept input independently, so you can translate either way.
Roman Numerals FAQ
How are large numbers represented?
With the vinculum: an overline multiplies the symbols under it by 1,000, so V with a bar is 5,000 and M with a bar is 1,000,000. A double overline multiplies by 1,000,000. The tool renders these with combining overline characters and decodes them when pasted back.
How is an invalid numeral detected?
The parser first computes the value using subtractive rules, then converts it back and compares; if the round trip does not reproduce your input, the numeral is rejected as malformed.
Does case matter?
No. Lowercase letters are uppercased automatically and any non-IVXLCDM characters are stripped as you type.