Roman Numeral Converter
Convert whole numbers into Roman numerals and back again. Enter one value per line to convert a whole list at once — results update instantly and never leave your browser.
Conversions will appear here.
How to use Roman Numeral Converter
- 1
Choose a direction
Pick Number to Roman to turn whole numbers into Roman numerals, or Roman to Number to read numerals back as digits. The swap button flips the two.
- 2
Type or paste your values
Enter one value per line. You can convert a single number like 2024 or a whole list at once, and the results update as you type.
- 3
Read the result
Each line is converted independently. If a value is out of range or not a valid numeral, a clear message explains exactly what to fix.
- 4
Copy the output
Use the copy button to grab every converted line at once, ready to paste into a document, a spreadsheet, or a design.
Understanding the Roman Numeral System
The seven letters and their values
Roman numerals are built from just seven letters, each tied to a fixed value: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500, and M is 1000. There is no symbol for zero, and there is no single letter larger than M. Every numeral you will ever read or write is some arrangement of these seven characters.
A handy memory aid for the order is the phrase "I Value Xylophones Like Cows Dig Milk," whose initials spell I, V, X, L, C, D, M from smallest to largest. Once the values are second nature, reading numerals becomes a matter of applying two simple rules: addition and subtraction.
Additive notation
The default rule is addition. When letters are written in order from largest to smallest, you simply add their values together. So VIII is 5 plus 1 plus 1 plus 1, which is 8. The numeral MDCLXVI walks straight down the value scale, 1000 plus 500 plus 100 plus 50 plus 10 plus 5 plus 1, totaling 1666.
Numerals were originally almost entirely additive, which is why old monuments and books sometimes show IIII for 4, and why many clock faces still do to this day. This converter, however, follows the standard modern rule and writes 4 as the subtractive IV. Additive forms are easy to read because the math runs left to right, but they get long fast, which is exactly the problem subtractive notation was invented to solve.
Subtractive notation
To avoid four-letter runs, Roman numerals use subtraction: a smaller letter placed before a larger one is subtracted from it. So IV is 5 minus 1, which is 4, and IX is 10 minus 1, which is 9. The same idea scales up: XL is 40, XC is 90, CD is 400, and CM is 900.
Only six subtractive pairs are valid, and they follow a pattern. I subtracts from V and X; X subtracts from L and C; C subtracts from D and M. You never subtract V, L, or D, and you never skip more than one tier, so IC for 99 is wrong. The correct form is XCIX, which is 90 plus 9.
The rules that keep numerals valid
Two constraints make a numeral well-formed. First, the additive letters I, X, C, and M may repeat at most three times in a row, so III is fine but IIII is not. The letters V, L, and D never repeat at all, because two of them would just equal the next letter up. That is why VV is invalid; it is simply X.
Second, a subtractive prefix is used only when it shortens the numeral. This converter rebuilds every numeral from scratch using these rules and rejects anything that does not match the one canonical spelling. That is why entries like IIII, VV, or IC are flagged as invalid even though a person might guess their intended value.
Converting a number step by step
To turn a number into Roman numerals, work from the largest place value down, subtracting the biggest symbol that fits at each step. Take 2024. Pull out two thousands as MM, leaving 24. There are no hundreds and no tens that reach 24 cleanly, but 20 is XX, leaving 4. Finally 4 is the subtractive IV. Join them and 2024 is MMXXIV.
The same routine handles any value. For 1994 you take M for 1000, then CM for 900, then XC for 90, then IV for 4, giving MCMXCIV. Reading backward reverses the process: scan left to right, add when values descend, and subtract when a smaller value sits before a larger one.
Range, limits, and larger numbers
Standard Roman numerals cover 1 to 3999. The ceiling is MMMCMXCIX, because four thousand would need MMMM, which breaks the three-repeat rule, and there is no single letter for 5000. With no zero and no negatives, the system is built purely for counting whole quantities.
To go higher, the Romans used a vinculum, an overline that multiplies a letter by 1000, so a barred V meant 5000 and a barred X meant 10,000. This notation is historically genuine but rare today and hard to type, so it sits outside this converter, which focuses on the everyday 1-to-3999 range you actually encounter.
Where Roman numerals still appear
Despite being ancient, the system is everywhere. Clock and watch faces use I through XII. The Super Bowl is numbered in Roman numerals, as are movie sequels, monarchs and popes such as Henry VIII or John Paul II, and the copyright year in film and television credits. Formal outlines and book front matter use them for chapters, sections, and preface page numbers.
Knowing how to read them turns a cornerstone date like MCMLXXXIV into 1984 at a glance, or tells you that Super Bowl LVIII was the 58th. Because the system has barely changed in two thousand years, the same rules that decoded an inscription in ancient Rome decode the credits on a film made yesterday.
Frequently asked questions
How do I convert a number to Roman numerals?
What is the largest number in Roman numerals?
How are Roman numerals written?
Why is my Roman numeral marked invalid?
Can I convert several numbers at once?
Related tools
Keep going with these handy tools