Roman Numeral Converter
Convert numbers to roman numerals and back, both ways, as you type.
This converts numbers to Roman numerals and back, for values from 1 to 3,999.
It follows standard subtractive notation, which is the part that produces most errors.
How Roman numerals work
Roman numerals use seven letters: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000. Values are normally written largest to smallest and added together.
The complication is subtractive notation. When a smaller value precedes a larger one, it is subtracted: IV is 4, not IIII, and IX is 9. Only six pairs are valid — IV, IX, XL, XC, CD and CM — and any other subtraction is not standard.
That is why long numerals look intimidating and are actually simple once split. MCMXCIV is M (1000) + CM (900) + XC (90) + IV (4) = 1994. Read left to right in chunks and it falls apart neatly.
Each subtractive pair is one chunk, not two separate letters. Reading them individually is what makes long numerals confusing.
What to enter
- Number
- From 1 to 3,999. Standard Roman numerals have no zero and no way to write larger values without extra notation.
- Roman numeral
- To convert back. Case is ignored, and the tool validates that the notation is standard.
The letters and the valid subtractions
- I, V, X
- 1, 5, 10.
- L, C
- 50, 100.
- D, M
- 500, 1000.
- The six subtractive pairs
- IV (4), IX (9), XL (40), XC (90), CD (400), CM (900). No others are standard.
- Maximum
- MMMCMXCIX = 3,999. Beyond that needs an overline notation for thousands.
What this assumes
Standard notation allows a letter to repeat at most three times, which is why 4 is IV rather than IIII.
There is no zero and no negative numbers. The system was built for counting, not for arithmetic.
How to calculate Roman numerals
Work down from the largest value, taking as many of each as fit.
- values
- 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1
- subtractive pairs
- Included in that list, which is why the method never produces IIII
Start with the largest value that fits. For 1994: M is 1000, leaving 994.
Take the next largest, including subtractive pairs. 900 fits, written CM, leaving 94.
Continue down the list. 90 is XC, leaving 4. Then 4 is IV, leaving 0.
Read it back to check. M + CM + XC + IV = 1000 + 900 + 90 + 4 = 1994.
See a worked example: a year, converted both ways
- Number
- 1994
1994 − 1000 = 994, so M.
994 − 900 = 94, so CM.
94 − 90 = 4, so XC.
4 − 4 = 0, so IV. The result is MCMXCIV, and 2026 by the same method is MMXXVI.
MCMXCIV
Frequently asked questions
Standard notation limits a letter to three repeats, so 4 uses subtraction: I before V means 5 − 1.
IIII does appear historically, and famously on many clock faces, where it is used for visual balance against the VIII opposite. It is not standard notation.
Only six pairs: IV (4), IX (9), XL (40), XC (90), CD (400), CM (900).
Others such as IL for 49 or IC for 99 are not standard. 49 is XLIX and 99 is XCIX, each built from valid pairs.
MMMCMXCIX = 3,999 in standard notation, since M cannot repeat more than three times.
Larger values used an overline (a vinculum) meaning multiply by 1,000, so V with a bar is 5,000. It is rarely used and not widely supported in plain text.
No. The system had no concept of zero as a number, which is one reason arithmetic with Roman numerals is so awkward.
Medieval scholars occasionally used *nulla*, the Latin for nothing, but it was never part of the numeral system itself.
Clock faces, book chapters and page prefaces, film and television copyright dates, monarch and pope names, Super Bowl numbering, and building cornerstones.
They also remain popular for tattoos of significant dates, which is a common reason people look up a conversion.
Split it into chunks left to right, treating each subtractive pair as one unit. MCMXCIV is M | CM | XC | IV.
Then add: 1000 + 900 + 90 + 4 = 1994. The mistake is reading letter by letter, which turns CM into 100 and 1000 rather than 900.
Problems people actually run into
Reading subtractive pairs as separate letters
In MCMXCIV, the CM is a single unit worth 900. Read as C then M it becomes 100 + 1000, and the whole answer is wrong.
Whenever a smaller letter sits before a larger one, they belong together. Chunk first, then add.
Inventing subtractions that are not valid
IL for 49 and IC for 99 look sensible and are not standard. Subtraction is only allowed with the six recognised pairs.
49 is XLIX (40 + 9) and 99 is XCIX (90 + 9). Building from the valid pairs always produces correct notation.
Results are estimates for general information only and are not professional financial, medical, or legal advice. Read our full disclaimer.
Last updated: September 4, 2026