Roman Numeral Converter: Numbers to Roman and Back
Convert numbers to Roman numerals and Roman numerals to numbers, from 1 to 3,999 or up to 3,999,999 with the overline. Strict validation, additive forms, decimal or hex input. Nothing is uploaded.
An overline (vinculum) multiplies a letter by 1,000, up to 3,999,999.
About the Roman Numeral Converter
The Roman Numeral Converter turns whole numbers into Roman numerals and Roman numerals back into numbers. It writes the standard modern subtractive form, such as MCMXCIV for 1994, and checks Roman input strictly, so a numeral that is not in standard form is explained rather than silently accepted. Numbers can be typed in decimal or hexadecimal, and a parsed numeral is shown in both. With Large numbers on, the converter uses the overline (vinculum) for values up to 3,999,999. Everything runs in your browser, and nothing is uploaded.
How to use it
Number to Roman
- Leave Direction on Number to Roman.
- Choose the Input base: Decimal, or Hexadecimal to convert a value such as
7CAor0x7ca. - Type the number. The Roman numeral appears below with a Copy button.
- For numbers from 4,000 to 3,999,999, turn on Large numbers.
Roman to number
- Choose Roman to number and type the numeral. Upper and lower case both work.
- Read the value in decimal and hexadecimal, each with a Copy button.
- To read older or informal forms such as IIII on a clock face, turn on Accept additive forms.
Privacy
The conversion is done by code on this page, in your browser. Nothing you type is sent anywhere, and nothing is kept once you close the tab.
Reference table
| Numeral | Value | Numeral | 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 | 1,000 | MMMCMXCIX | 3,999 |
The rules of standard form
Adding and subtracting
Letters are written from the largest value to the smallest and added together: MDCLXVI is 1,000 + 500 + 100 + 50 + 10 + 5 + 1 = 1,666. Six pairs subtract instead: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). Only I, X and C are placed before a larger letter, and only before the next two letters up, so 99 is XCIX, not IC.
What strict validation rejects
In standard form no letter is repeated more than three times, and V, L and D are never repeated or subtracted. The converter rejects IIII (write IV), VX, IC (write XCIX for 99) and IIX (write VIII for 8), and when a numeral can be read but is not standard, it tells you the standard spelling of the same value. Accept additive forms relaxes the repetition rule, so IIII reads as 4 and XXXXVIIII as 49, but letters still must not increase except in the six subtractive pairs.
Large numbers and the vinculum
Standard Roman numerals stop at 3,999 (MMMCMXCIX), and there is no numeral for zero or for negative numbers. A line drawn over a letter, the vinculum, multiplies it by 1,000: V̅ is 5,000 and X̅ is 10,000. With Large numbers on, values from 4,000 are written with the thousands overlined and the rest plain, so 4,000 is I̅V̅ and 3,999,999 is M̅M̅M̅C̅M̅X̅C̅I̅X̅CMXCIX. The overline is the Unicode combining character U+0305, so the result copies into documents as text. Some fonts draw it slightly offset.
Where Roman numerals are still used
Clock faces, book chapters and appendices, the names of monarchs and popes, film copyright years, sporting events such as the Super Bowl, and outline numbering all use Roman numerals. Copyright years are a common reason to convert: MMXXIV is 2024.
Related tools
To convert between binary, octal, decimal and hexadecimal, use the Number Base Converter or go straight to Hex to Decimal. To work out the number of years between two dates before writing them as numerals, use the Date Calculator.
Open-source credits
- The converter is written for this site and uses no third-party library.
- Numerals follow the standard modern subtractive notation (I, V, X, L, C, D, M with the pairs IV, IX, XL, XC, CD and CM), and large numbers use the vinculum written with the Unicode character U+0305 COMBINING OVERLINE from the Unicode Standard.
Frequently asked questions
What is the largest number in Roman numerals?
In standard form the largest is 3,999, written MMMCMXCIX, because no letter may be repeated more than three times. With Large numbers on, a line over a letter multiplies it by 1,000, which extends the range to 3,999,999.
Is there a Roman numeral for zero?
No. The Roman system has no symbol for zero or for negative numbers, so the converter starts at 1. Medieval writers sometimes used the word nulla, meaning none, but it was never part of the numeral system.
Why does the converter reject IIII?
The standard modern form writes 4 as IV, so strict validation reports IIII and gives the standard spelling. IIII does appear on many clock faces. Turn on Accept additive forms to read IIII, VIIII and similar forms.
How do I write 2024 in Roman numerals?
2024 is MMXXIV: MM for 2,000, XX for 20 and IV for 4. Type any year to get its numeral, or switch the direction to read a numeral such as a film copyright year.
Can I convert hexadecimal to Roman numerals?
Yes. Choose Hexadecimal as the input base and type the value, with or without a 0x prefix, for example 7CA for 1994. When you convert a Roman numeral to a number, its hexadecimal value is shown next to the decimal one.