What is the range of Roman numerals?

Standard Roman numerals run from 1 (I) to 3999 (MMMCMXCIX). There is no symbol for zero, and numbers above 3999 require bars (vinculum) that fall outside the classic notation, so this tool validates and limits input to 1–3999.

What is subtractive notation?

Instead of writing IIII for 4, the standard form places a smaller symbol before a larger one to subtract it: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). This converter always produces and accepts these six canonical pairs.

Is my input uploaded anywhere?

No. The conversion runs entirely in your browser with plain JavaScript. Nothing is sent to a server, logged or stored, and it keeps working offline once the page has loaded.

Roman Numeral Converter — Number to Roman & Back (1–3999)

Roman Numeral Converter

Convert both ways and live: type a number (1–3999) to get its Roman numeral, or type a Roman numeral to get the number. It uses proper subtractive notation (IV, IX, XL, XC, CD, CM) and validates your input as you type — all 100% in your browser.

Number → Roman (1–3999)

Roman

Roman → Number

Number

Quick examples:

🔒 100% private — runs in your browser, never uploaded.

How to use the Roman numeral converter

Number to Roman: type a whole number from 1 to 3999 in the left box. The Roman numeral appears instantly below it.
Roman to number: type a Roman numeral (such as MMXXVI) in the right box. Letters are auto-capitalised, and the decimal value appears below.
Tap an example chip to fill the number box with a classic tricky value like 4, 444 or 1994.
Copy either result with the button beside it.

How Roman numerals work

Roman numerals combine seven letters — I (1), V (5), X (10), L (50),C (100), D (500) and M (1000). You read them left to right, adding each symbol's value. So MMXXVI is 1000 + 1000 + 10 + 10 + 5 + 1 = 2026. When a smaller symbol sits directly before a larger one, it issubtracted instead — that is the modern standard known as subtractive notation.

There are exactly six subtractive pairs: IV (4), IX (9), XL (40), XC (90),CD (400) and CM (900). They exist so that no symbol repeats more than three times in a row — which is why 4 is IV rather than IIII, and 90 is XC rather than LXXXX. This tool always outputs the canonical form and only accepts well-formed numerals, so you can trust the result for dates, book chapters, clock faces, movie sequels and monument inscriptions.

Is it private?

Yes. Everything happens locally in your browser using a small piece of plain JavaScript — there is no server round-trip, no logging and no upload. You can even use it offline once the page has loaded. Because nothing leaves your device, it is perfectly safe for any value, whether you are decoding a copyright year or naming the next king in your story.

Frequently asked questions

Why can't I convert 0 or negative numbers?

The Roman system has no symbol for zero and no concept of negative quantities, so valid numerals start at 1. Inputs of 0, blanks or negatives are flagged with an error instead of a misleading result.

What is the largest value, 3999?

Without overline (vinculum) notation the largest standard numeral is MMMCMXCIX = 3999, because you can show at most three Ms. This converter sticks to that classic, unambiguous range.

Does it accept lowercase letters?

Yes. Type mcmxciv or MCMXCIV — the Roman box upper-cases your input automatically before converting.

Why does IIII or IC show an error?

Those are not valid standard numerals. Four Is in a row and skip-a-step subtractions like IC break the rules, so the tool rejects them rather than guessing what you meant.