A Roman Numeral Converter translates between the Arabic numbers we use every day and the letter-based numerals of ancient Rome. Roman numerals build values from seven symbols — I, V, X, L, C, D, and M — combined by addition and, in a handful of cases, subtraction. This tool converts a number such as 2024 into MMXXIV, and reads a numeral such as MCMLXXXIV back as 1984, in both directions from a single box.
The system is additive at heart: symbols are written from largest to smallest and summed, so XVII is 10 + 5 + 1 + 1 = 17. The wrinkle is subtractive notation, where a smaller symbol placed before a larger one is subtracted rather than added — IV is 4, not 6, and CM is 900. Standard modern usage allows only six subtractive pairs (IV, IX, XL, XC, CD, CM) and never repeats a symbol more than three times, which is why 4 is IV and not IIII.
This converter enforces those rules in both directions. Encoding always produces the canonical spelling, and decoding validates the input by round-tripping it: a numeral is accepted only if it is exactly the standard spelling of its own value, so malformed strings like IIII, VX, or IC are caught and corrected. Because there is no Roman symbol for zero and no plain-ASCII symbol for 5000, the tool works over the conventional 1 to 3999 range, and it all runs in your browser with nothing uploaded.
Type an Arabic number such as 2024 to get Roman numerals, or paste a numeral such as MMXXIV to decode it. The tool detects which you mean and can be switched manually.
The conversion appears as you type. Encoding gives the canonical numeral; decoding gives the number and shows the normalized spelling so you can confirm the input was valid.
See how the numeral splits into its additive parts — MCMXCIV as M + CM + XC + IV — which makes the subtractive pairs easy to understand and verify.
Copy the result with one click, or tap a quick-fill button for common values like 4, 9, 40, or the current year to see the rules in action.
Encode numbers to numerals and decode numerals to numbers from the same input. Encoding always yields the canonical form, and decoding round-trips it to guarantee the two agree.
Malformed numerals such as IIII, VX, or IC are rejected with a message that suggests the correct spelling, because a valid numeral must equal the canonical spelling of its own value.
Every numeral is shown split into its additive components, so you can see exactly why MCMXCIV is 1994 and how each subtractive pair contributes.
Digits are treated as a number to encode; a string of I, V, X, L, C, D, and M is treated as a numeral to decode. A manual switch is always available.
Convert integers between binary, octal, decimal, hexadecimal, and any base from 2 to 36 with exact BigInt precision and live bit and byte counts
Convert length, weight, temperature, area, volume, speed, time, data, pressure, energy, and angle units instantly with exact conversion factors
Translate text to binary and binary to text, plus hexadecimal, decimal, and octal, with full UTF-8 support
0 comments
No comments yet. Be the first to share your thoughts!