Roman Numeral Converter
Convert between numbers (1-3999) and Roman numerals with step-by-step explanations. Validate Roman numerals and view your conversion history. All calculations happen locally — nothing leaves your browser.
How do Roman numerals work? Roman numerals build numbers from seven letters — I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000 — written from largest to smallest and added together, so XVII is 10 + 5 + 1 + 1 = 17. The one exception is subtractive notation: a smaller symbol placed before a larger one is subtracted, giving IV = 4, IX = 9, XL = 40, XC = 90, CD = 400 and CM = 900.
How to Use the Roman Numeral Converter
- Choose the direction — Number → Roman turns 2024 into MMXXIV; Roman → Number does the reverse. The input box swaps to match, so you never have to clear the wrong field.
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Enter the value — Numbers must be whole and between 1 and 3999, the range expressible without an overline. Roman input is case-insensitive —
mcmxcivandMCMXCIVare read the same way. - Check the validation line — The line under the input confirms the reading, for example Valid Roman numeral: MMXXIV = 2024. It turns to an error when a character is not one of I, V, X, L, C, D or M, or when the total falls outside 1–3999.
- Read the step-by-step breakdown — The steps panel decomposes the number by place value — thousands, hundreds, tens, units — and names the symbol used for each part, which is the same method you would use on paper.
- Reuse earlier conversions — The history list keeps the conversions you have made since the page loaded, so you can compare several dates or chapter numbers side by side without retyping them. Reloading the page clears it.
- Copy the result — Copy Result puts the converted value on the clipboard, ready for a document title, a slide or an engraving brief.
How Roman Numerals Are Built
The system is additive at heart: write the symbols in descending order and add them up. MMXV is 1000 + 1000 + 10 + 5 = 2015. Because there is no positional notation and no zero, the symbols themselves carry the magnitude, which is why the same digit-shape never means different things in different positions the way 2 does in 25 and 52.
Layered on top is subtractive notation, which keeps numerals short by allowing one smaller symbol before a larger one to mean the difference. Without it, 4 would be IIII and 900 would be DCCCC. Only six such pairs are valid, and they follow a strict rule: only the powers of ten (I, X, C) may be subtracted, and only from the next two symbols above them.
Symbol Values and Subtractive Pairs
| Symbol | Value | Subtractive pair | Value |
|---|---|---|---|
| I | 1 | IV | 4 |
| V | 5 | IX | 9 |
| X | 10 | XL | 40 |
| L | 50 | XC | 90 |
| C | 100 | CD | 400 |
| D | 500 | CM | 900 |
| M | 1000 | — | — |
The Rules That Make a Numeral Valid
- I, X, C and M may repeat up to three times in a row. Four in a row is written with a subtractive pair instead: 40 is XL, not XXXX.
- V, L and D never repeat. Two of them would always equal the next symbol up, so VV is written X and LL is written C.
- Only I, X and C can be subtracted, and only from the next two larger symbols. IV and IX are legal; IL and IC are not, because 49 is XLIX and 99 is XCIX.
- A subtracted symbol appears once. IIX is never used for 8; that is VIII.
- Values descend left to right, apart from the subtractive pairs, so MCMXCIV reads as M + CM + XC + IV.
Converting by Place Value
The reliable manual method — and the one this converter follows — is to split the number into thousands, hundreds, tens and units, convert each part on its own, then join them. Nothing ever carries between the groups, which is what makes the method safe:
1994 = 1000 + 900 + 90 + 4 = M + CM + XC + IV = MCMXCIV
Reading a numeral back is the mirror image. Scan from left to right and add each symbol's value, except when a symbol is smaller than the one immediately after it — then subtract it instead. In MCMXCIV: M adds 1000; C is smaller than the M after it so subtract 100 then add 1000, giving 900; X is smaller than the following C so that pair gives 90; I before V gives 4. Total 1994.
Limits of the System
There is no symbol for zero and no way to write a negative number or a fraction in standard notation, which is a large part of why positional Arabic numerals eventually replaced Roman ones for arithmetic. Medieval scribes occasionally wrote nulla, Latin for nothing, where a zero was needed, but it was a word rather than a numeral.
The practical ceiling is 3999 (MMMCMXCIX), since M cannot repeat more than three times. Larger values used a vinculum, an overline meaning multiply by 1,000, so an overlined V is 5,000 and an overlined X is 10,000. That convention is not widely supported in plain text and is outside this converter's range.
Clock faces are the famous exception to the rules above: most traditional dials print IIII rather than IV for four. The habit long predates any single explanation offered for it — visual balance against the VIII opposite is the usual one — and it is a stylistic convention rather than valid standard notation, so this converter produces IV.
Frequently Asked Questions
In standard notation, MMMCMXCIX (3999) is the largest. For larger numbers, Romans used a vinculum (overline) to multiply by 1,000. For example, V = 5,000 and X = 10,000.
No — the Roman numeral system had no concept of zero. The word "nulla" (meaning "nothing") was sometimes used in medieval texts, but it wasn't a formal Roman numeral.
Break the number into place values: 1984 = 1000 + 900 + 80 + 4. Convert each: 1000 = M, 900 = CM, 80 = LXXX, 4 = IV. Combine them: MCMLXXXIV. This tool converts any number up to 3999 to Roman numerals and back automatically.
Standard notation allows a symbol to repeat at most three times, so IIII is replaced by the subtractive pair IV. Clock and watch dials are the well-known exception and usually print IIII, a stylistic convention rather than a correction to the rules. This converter follows the standard form and outputs IV.
Subtraction is only allowed from the next two symbols above the one being subtracted, so I may precede only V and X, X may precede only L and C, and C may precede only D and M. IC would jump from 1 to 100 and is invalid. Ninety-nine is built place by place: 90 is XC and 9 is IX, giving XCIX.
No. Both directions of conversion, the validation and the history list run entirely in JavaScript on your device. Nothing is uploaded, and the page keeps working offline once loaded.
The reader rejects any character that is not I, V, X, L, C, D or M — a stray space inside the numeral, a letter O typed for a zero, or punctuation will all stop it — and it rejects totals outside 1 to 3999. Note that the reader is deliberately forgiving about form: it will still add up a non-standard spelling such as IIII and report 4, so a green line means readable rather than correctly written. Use the rules above to check the form itself.
Mostly where a number is decorative or needs to look distinct from ordinary figures: clock faces, book chapters and front-matter page numbers, film and building copyright dates, monarch and pope regnal numbers such as Elizabeth II, Super Bowl editions, and chord degrees in music theory. For arithmetic they were abandoned centuries ago in favour of positional decimal notation.
Use Cases
Reading a Building's Date Stone
Someone photographing a facade marked MCMXXXVII decodes it to 1937 to date the building before filing a heritage query.
Numbering Front Matter in a Book
An editor converts page counts to lowercase Roman numerals so the preface runs i to xiv before Arabic numbering restarts at chapter one.
Transcribing an Archive Document
A researcher working through a parish register converts each Roman-numbered entry to ordinary figures so the dates can be sorted in a spreadsheet.
Setting a Date on an Invitation
A designer laying out a wedding invitation converts the year to MMXXVI and checks the validation line before the piece goes to print.
Branding a Numbered Event
Anyone naming the ninth edition of a conference or tournament checks that IX is the correct form before it goes on badges and signage.