How to use the Roman Numeral Converter
- Enter a number to see its Roman form.
- Or type a Roman numeral to read it back as a number.
- Both conversions run at once, so you can check one against the other.
- Stick to values from 1 to 3999 for standard notation.
How the calculation works
Roman numerals are additive with seven symbols — I 1, V 5, X 10, L 50, C 100, D 500, M 1000 — read left to right and summed. Subtractive notation shortens four repeated symbols: IV rather than IIII, IX rather than VIIII, XL rather than XXXX. Only six subtractive pairs are valid, and only powers of ten may be subtracted, and only from the next two higher symbols.
The greedy conversion algorithm works because the symbol values, extended with the subtractive pairs, form a canonical system: repeatedly take the largest value that fits and subtract it. Reading in the other direction uses a single rule — if a symbol is smaller than the one after it, subtract it, otherwise add it.
There is no zero and no place value, which is why arithmetic in Roman numerals is so painful and why the system was displaced. The standard range stops at 3999, since 4000 would need four M symbols; historical texts use an overline (vinculum) to multiply by a thousand, but that convention is not universally supported in plain text.
Symbols: I=1 V=5 X=10 L=50 C=100 D=500 M=1000 ; subtractive pairs: IV IX XL XC CD CMSource: Standard Roman numeral notation as codified in modern usage; subtractive-pair conventions.
Worked example
Writing the year 2026 for a building inscription.
- 2000 → MM.
- 20 → XX.
- 6 → VI.
MMXXVI — read back it is 1000+1000+10+10+5+1 = 2026.
Frequently asked questions
Why is 4 written IV and not IIII?+
Subtractive notation is the modern standard, though IIII still appears on many clock faces for visual balance.
Is there a Roman numeral for zero?+
No. The system has no zero and no concept of place value.
What is the largest standard Roman numeral?+
MMMCMXCIX, or 3999. Larger values need an overline convention.
Can I subtract any symbol?+
No. Only I, X and C may be subtracted, and only from the next two larger symbols.
Last reviewed September 1, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.