Both directions
Numbers become Roman numerals and numerals become numbers, with auto-detection that reads what you typed and converts the right way.
Number → Roman · Roman → Number · Auto-detect · No upload
Roman Numeral Converter
Convert any number to Roman numerals and any Roman numeral back to a number, instantly as you type. Auto-detection figures out which way you are going, vinculum notation extends the range to 3,999,999, strict validation flags malformed numerals, and a breakdown shows exactly how each letter adds up. Everything runs in your browser — no upload, no sign-up.
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Breakdown — how the value is built
One value per line
Result
Ready
Key features
Vinculum range
An overline multiplies a letter by 1000, so the converter reaches 3,999,999 instead of stopping at the classic limit of 3999.
Strict validation
Malformed numerals like IIII or VX are caught and explained, so you only ever copy a canonical, correctly formed Roman numeral.
Breakdown view
See each numeral split into its additive and subtractive parts — M + CM + XC + IX — to understand exactly how the total is built.
Frequently asked questions
How do I write a number in Roman numerals?
Type the number and read the result. Roman numerals use seven letters — I=1, V=5, X=10, L=50, C=100, D=500, M=1000 — written from largest to smallest, with subtractive pairs such as IV=4, IX=9, XL=40 and CM=900.
What does the overline (vinculum) mean?
A bar over a letter multiplies its value by 1000. So V̄ is 5000 and X̄ is 10,000. Enable the Vinculum range to convert numbers from 4000 up to 3,999,999. The overline copies along with the text as a combining character.
Why won't it accept IIII or VX?
With strict validation on, only canonical numerals are accepted: a letter repeats at most three times, and only I, X and C may be subtracted, each from the next two larger letters. Turn strict validation off to read loose forms like IIII as 4.
Is there a Roman numeral for zero?
No. The system is additive and has no zero symbol, so the converter accepts whole numbers from 1 upward. Medieval scribes occasionally wrote the word nulla for nothing, but never a numeral.
Is my data sent anywhere?
No. All parsing and conversion happen locally in your browser. Nothing is uploaded, and the page works offline once loaded.