# Roman numerals converter

> Numbers to numerals and back, with the canonical subtractive form, the place-by-place construction, and honest validation: IIII is accepted and explained, IL is refused with the rule it breaks.

- Tool: https://ronutz.com/en/tools/roman-numerals
- Family: Encoding & data

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## What it does

Type a number (1 to 3999) and read its Roman numeral; type a numeral and read its value. The tool always shows the canonical subtractive form and how it is built place by place: 1994 is M + CM + XC + IV. Everything is computed in your browser.

## Honest validation

Historical additive spellings the Romans themselves used - IIII on clock faces, MDCCCCX on building facades - are accepted, valued correctly, and flagged with the canonical form beside them. Truly malformed strings are refused with the specific rule they break: IL is not a legal subtractive pair (only IV, IX, XL, XC, CD, CM subtract), VV repeats a symbol that never repeats, IIX subtracts two symbols where only one may be subtracted.

## Why it stops at 3999

The classical system has seven symbols, no zero, and nothing above M (1000). For larger values the Romans wrote a vinculum - an overline multiplying by 1000 - which has no plain-text form. Rather than invent a convention, the tool states the limit.

## Standards and references

- [Encyclopaedia Britannica — Roman numeral](https://www.britannica.com/topic/Roman-numeral) - symbols, subtractive principle, history
- [Unicode — Number Forms block (Roman numeral characters)](https://www.unicode.org/charts/PDF/U2150.pdf) - dedicated Unicode code points vs plain letters
- [Library of Congress — Why do clock faces use IIII?](https://www.loc.gov/everyday-mysteries/) - the additive IIII tradition

## Related reading

- [Roman Numerals: How the System Actually Works](https://ronutz.com/en/learn/roman-numerals-how-the-system-works.md): Seven symbols, no zero, and one subtraction rule that arrived a thousand years after Rome. Why IIII is on your watch and IV is in your textbook, what IL breaks, and why the classical system runs out of road at 3999.