Roman Numerals Converter
Convert any integer from 1 to 3,999,999 to Roman numerals or decode a Roman numeral back to an Arabic number. The converter also handles full dates (MM/DD/YYYY), shows a place-value breakdown so you can see exactly how each digit maps to symbols, and supports the vinculum (overline) notation for numbers above 3,999.
Worked example
2024 to MMXXIV: 2000 = MM, 20 = XX, 4 = IV. Reverse: MCMXCIX = M(1000) + CM(900) + XC(90) + IX(9) = 1999. Date: 07/04/1776 = VII/IV/MDCCLXXVI.
How Roman numeral conversion works
The conversion algorithm works greedily: starting with the largest possible symbol value (M = 1,000), it subtracts that value from the number as many times as it fits, appending the symbol each time, then moves to the next smaller value. The six subtractive pairs (IV, IX, XL, XC, CD, CM) are treated as single units in the lookup table, which is why 4 becomes IV rather than IIII. Reading in reverse, you scan left to right: if a symbol is smaller than the next symbol, you subtract it instead of adding it (IX = 10 - 1 = 9). The round-trip validation step confirms the decoded number re-encodes to exactly the input string, catching malformed numerals like IIII or VX before they return a wrong answer.
Date conversion and popular uses
Converting a date to Roman numerals is simply a matter of treating each part (month, day, year) as an independent number conversion. The results are written in the same order as the input date, separated by slashes. This format is especially popular for tattoos, wedding invitations, memorial inscriptions, and engravings where the date should be visually distinctive but still legible. Because most personal dates fall between 1 and 3,999, they fit neatly within the standard seven-symbol system without any extensions. Famous historical years like MDCCLXXVI (1776) or MCMXLIX (1949) are commonly used in coins, monuments, and academic seals.
Large numbers and vinculum notation
The standard seven-symbol system tops out at MMMCMXCIX (3,999). To represent numbers from 4,000 to 3,999,999, the vinculum (a horizontal bar placed over a symbol) multiplies that symbol by 1,000. So V with an overline represents 5,000, X with an overline represents 10,000, and M with an overline represents 1,000,000. Ancient Romans used this notation on milestones and in accounting, and modern encyclopedias and calculators extend it consistently. In digital text, the overline is rendered with a Unicode combining bar character. Toggle "Large numbers" in this converter to enable vinculum mode.
Place-value breakdown and reading rules
Understanding Roman numerals is easier when you break a number into its decimal places: thousands, hundreds, tens, and ones. Each place has its own set of symbols: M/CM/D/CD for thousands and hundreds, C/XC/L/XL for hundreds and tens, X/IX/V/IV for tens and ones, and I for ones. The five core rules are: (1) symbols are written largest to smallest, left to right; (2) at most three of the same symbol appear in a row; (3) V, L, and D are never repeated; (4) only I, X, and C can be used in subtractive notation; (5) only one smaller numeral may precede a larger one for subtraction. Breaking any of these rules produces an invalid numeral.
Roman numeral symbols and values
| Symbol | Value | Notes |
|---|---|---|
| I | 1 | From Latin "unus" |
| IV | 4 | Subtractive: 5 minus 1 |
| V | 5 | From Latin "quinque" |
| IX | 9 | Subtractive: 10 minus 1 |
| X | 10 | From Latin "decem" |
| XL | 40 | Subtractive: 50 minus 10 |
| L | 50 | Origin uncertain |
| XC | 90 | Subtractive: 100 minus 10 |
| C | 100 | From Latin "centum" |
| CD | 400 | Subtractive: 500 minus 100 |
| D | 500 | Half of M (an older symbol) |
| CM | 900 | Subtractive: 1000 minus 100 |
| M | 1000 | From Latin "mille" |
The seven core symbols and the six subtractive pairs that make up the complete standard system.
Frequently asked questions
Why does 4 use IV instead of IIII?
Classical Roman convention prohibits repeating the same symbol more than three consecutive times. IIII violates this rule, so the subtractive pair IV (5 minus 1) is used instead. This has been the standard in manuscripts and inscriptions since at least the medieval period, though some clock faces still use IIII for aesthetic reasons.
What is the largest number in standard Roman numerals?
Using the seven standard symbols without extensions, the largest number is 3,999, written MMMCMXCIX. You cannot represent 4,000 with a fourth M because the three-in-a-row rule limits M to three consecutive uses. Numbers above 3,999 require vinculum (overline) notation, which multiplies any symbol by 1,000.
How do I convert a date to Roman numerals for a tattoo?
Switch the mode to "Date to Roman numerals" and enter your date in MM/DD/YYYY format. Each part of the date is converted independently: the month, the day, and the year become separate Roman numerals joined by slashes. For example, 07/04/1776 becomes VII/IV/MDCCLXXVI. Many people also use just the year, such as MCMXCIX for 1999.
How do I read a Roman numeral I do not recognize?
Switch to "Roman numeral to number" mode and type the numeral using the seven letters I, V, X, L, C, D, M. The calculator decodes it left to right: each symbol is added to the total, except when a smaller symbol immediately precedes a larger one, in which case the smaller value is subtracted. The result is validated by re-encoding to confirm the numeral is well-formed.
Are Roman numerals still used today?
Yes. Roman numerals appear on clock faces, in chapter and section numbering, in film copyright notices, on Super Bowl and Olympic branding, in royal and papal names (Elizabeth II, Pope Francis I), on cornerstones and monuments, and in academic and legal contexts. They also remain popular for dates in tattoos and commemorative design because they look elegant and timeless.
What makes a Roman numeral invalid?
A numeral is invalid if it breaks any of the five core rules: the same symbol appears four or more times in a row; V, L, or D are repeated; a subtractive symbol that is not one of the six standard pairs (IV, IX, XL, XC, CD, CM) is used; more than one smaller numeral precedes a larger one; or the string does not round-trip correctly from Roman back to Arabic and back to the same Roman form. This converter flags such inputs rather than returning a wrong answer.