Roman numeral converter
Type a number to see it as a Roman numeral, or type a Roman numeral to read its value. Roman input is checked against the standard subtractive form, so invalid numerals are caught. It all runs in your browser.
Supports whole numbers from 1 to 3999.
Both directions
Open the tool in the direction you need — each has its own page:
How to convert Roman numerals
- Type a number (1–3999) into the number field, or a Roman numeral into the Roman field.
- The other field updates instantly.
- Copy whichever value you need.
About Roman numerals
Roman numerals use seven letters — I, V, X, L, C, D and M — combined in a subtractive system, so 4 is IV (one before five) and 9 is IX. They still appear on clock faces, in book chapters, film copyright dates, monarch and pope names, and event numbering such as the Olympics and the Super Bowl.
This converter goes both ways and validates Roman input against the canonical form, so you get a correct, standard numeral every time. It runs entirely in your browser — instant, private and free.
The subtractive rules are stricter than they look. Only I, X and C may be subtracted, and each only from the next two larger symbols: I before V or X, X before L or C, and C before D or M. That is why 99 is XCIX rather than IC, and 1999 is MCMXCIX rather than MIM. A single subtractor at a time is allowed, so 8 is VIII, never IIX.
To read a long numeral, break it into thousands, hundreds, tens and units and handle each group separately: MMXXVI is MM (2000), XX (20) and VI (6), so 2026. The same trick works in reverse when you want to sanity-check a converted value. One famous exception you will meet in the wild: many clock faces use IIII for 4 — a centuries-old typographic tradition, not standard notation, which is why validators reject it.
Frequently asked questions
How do I convert a number to Roman numerals?
Type the number (1–3999) into the number field and its Roman numeral appears instantly. Type a Roman numeral into the other field to convert back.
What numbers can I convert?
Standard Roman numerals cover 1 to 3999. There is no symbol for zero or negative numbers, and values above 3999 traditionally need an overline, which this tool does not use.
Does it check that a numeral is valid?
Yes. Roman input is validated against the canonical subtractive notation, so non-standard forms like IIII, VV or IC are rejected rather than silently accepted.
Is anything uploaded?
No. The conversion runs entirely in your browser; nothing is sent anywhere.
Why do some clocks use IIII instead of IV?
IIII on clock faces is a typographic tradition dating back centuries — it visually balances the VIII on the opposite side of the dial and was standard among clockmakers. It is not valid subtractive notation, though, so this converter (and most style guides) treats IV as the correct form for 4. If you are transcribing a clock face, write IV.