Convert Roman numerals to numbers and integers to Roman numerals in your browser. Auto-detects the direction and validates canonical form, from 1 to 3999.
Runs entirely in your browser — your data never leaves your device.
How to use Roman Numeral Converter
What it does & when you need it
Roman numerals still turn up in surprising places: clock faces, book prefaces,
movie copyright years, monarch and pope names, Super Bowl numbering, and the odd
tattoo. This converter goes both ways — type a number and get the numeral, or type
a numeral and get the number — and it figures out which direction you mean
automatically. It runs entirely in your browser, and it validates its input, so a
mistyped numeral is caught rather than quietly mis-decoded.
How to use
Type a whole number (1–3999) or a Roman numeral into the input buffer, or
press Sample to load one.
The tool auto-detects the direction — the status line tells you whether it
read a number or a numeral — and shows the conversion instantly.
Copy the result with Copy result or Ctrl/Cmd + Enter.
Things worth knowing
Direction is decided by the characters. All digits mean encode to a numeral;
the letters I V X L C D M mean decode to a number. Mixed input like 12X is
ambiguous, so it is rejected instead of guessed.
The range is 1 to 3999. There is no symbol for zero and no negative numerals,
and numbers of 4000 and above need a bar-over-letter notation this tool does not
use. Anything outside that window is reported as out of range.
Only canonical spellings are accepted. A symbol repeats at most three times,
so 4 is IV, never IIII, and only certain subtractive pairs are legal, so 99 is
XCIX, never IC. The tool validates by re-encoding the number and comparing, so
non-standard forms are flagged.
Case does not matter for decoding.mcmlxxxiv and MCMLXXXIV both read as
1984; encoded output is always uppercase. Need a different kind of conversion? The
Number Base Converter handles binary, hex, and
everything between.
Examples
Year to Roman numerals
2024
A number is auto-detected and encoded: 2024 becomes MMXXIV.
Roman numeral to number
MCMLXXXIV
Letters are decoded the other way: MCMLXXXIV is 1984.
Subtractive notation
44
Shows the subtractive pairs at work: 44 is XLIV (XL for 40, IV for 4).
Lowercase decodes too
xiv
Decoding is case-insensitive, so xiv reads as 14.
Frequently asked questions
How does auto-detection decide which way to convert?+
If the input is all decimal digits it is treated as a number and encoded to a Roman numeral; if it is made of the letters I, V, X, L, C, D, and M it is decoded to a number. Mixed input like 12X is rejected, so you never get an ambiguous result.
What range of numbers can be represented?+
Standard Roman numerals cover 1 to 3999. There is no zero and no negatives, and 4000 and up need a bar-over-letter (vinculum) notation this tool does not use, so values outside 1–3999 are reported as out of range.
Does it accept lowercase numerals?+
Yes. Decoding is case-insensitive, so mcmlxxxiv and MCMLXXXIV both return 1984. Encoding always outputs uppercase letters, which is the conventional written form.
Why is IIII or IC rejected as invalid?+
Because they are not canonical. The rules allow at most three repeats of a symbol (so 4 is IV, not IIII) and only specific subtractive pairs (I before V or X, X before L or C, C before D or M) — so 99 is XCIX, never IC. The tool validates by re-encoding and rejects any non-standard spelling.
What are Roman numerals still used for?+
Clock faces, book chapter and page prefixes, film sequels and copyright years, monarch and pope names (Elizabeth II), and Super Bowl numbering. Everything is computed locally in your browser, so nothing you enter is sent anywhere.