Roman Numeral Converter
Convert numbers to Roman numerals and back, from 1 to 3999, with full validation of the numeral you enter.
How it works
Symbols: I=1, V=5, X=10, L=50, C=100, D=500, M=1000 · a smaller symbol before a larger one subtracts (IV = 4, CM = 900)
Roman numerals combine seven letters using addition and a limited subtraction rule: a smaller symbol placed before a larger one is subtracted, which is why IV is 4 and IX is 9. Standard form allows only six subtractive pairs (IV, IX, XL, XC, CD, CM) and never repeats a symbol more than three times, so 4 is IV, never IIII. The system has no zero and tops out at 3999 (MMMCMXCIX) without special overlines.
Worked example
2024 breaks into 1000 + 1000 + 10 + 10 + (5 − 1), i.e. MM + XX + IV = MMXXIV. Reading it back, MM = 2000, XX = 20, IV = 4, totalling 2024.
Sources: Roman numerals — Wikipedia
Frequently asked questions
Why is 4 written IV and not IIII?
Standard Roman numerals use a subtractive rule to avoid four repeats: placing I before V means “one less than five,” so 4 is IV. (Clock faces sometimes use IIII for visual balance, but that is a stylistic exception.)
What is the largest number I can write?
Using the basic seven symbols, 3999 (MMMCMXCIX). Larger values historically used an overline to multiply by 1000, but that is not part of standard ASCII numerals, so this tool stops at 3999.
Is there a Roman numeral for zero?
No. The Roman system has no symbol for zero — the concept was written as the word “nulla.” That is why the numerals begin at 1.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.