Roman Numeral Converter
Convert between Arabic numbers and Roman numerals (1–3999).
Roman Numeral
Arabic Number
What is a Roman Numeral Converter?
A Roman numeral converter translates values between everyday Arabic numbers (1, 2, 3) and the numeral system of ancient Rome (I, II, III). Enter a number from 1 to 3999 to get its numeral with a step-by-step breakdown, or type a numeral to get its Arabic value with a validity check.
Roman numerals still appear on clock faces, in book chapters, in movie copyright years, on cornerstones, in royal names such as Charles III, and in event numbering like the Super Bowl. The 1–3999 range covers the classic system: Roman numerals have no zero, and 4000 or more traditionally needs an overline that multiplies a symbol by 1,000, which plain text handles poorly.
How the Conversion Works
The system uses seven symbols and two rules. Add each symbol's value as you read left to right, except when a smaller symbol sits before a larger one — then subtract it:
I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000
Value = sum of symbol values, subtracting any symbol that precedes a larger one
Subtraction is allowed in only six fixed pairs: IV (4), IX (9), XL (40), XC (90), CD (400), and CM (900). A symbol may repeat up to three times (III = 3), but V, L, and D never repeat. Conversion works greedily from M down to I, taking each value as many times as possible.
- Number (1–3999) — the whole number to convert on the Number to Roman tab.
- Roman Numeral — the numeral to convert on the Roman to Number tab; case does not matter.
- Breakdown — the additive chunks behind a result, shown as M+CM+XC+IV for 1994.
- Valid — the Yes/No verdict for Roman to Number input against the formation rules.
Worked Example: Converting 1994 and Reading MCMLXXXVII
Converting 1994 takes four greedy steps:
- 1994 ≥ 1000, so take M; 1994 − 1000 = 994 remains.
- 994 ≥ 900, so take CM; 994 − 900 = 94 remains.
- 94 ≥ 90, so take XC; 94 − 90 = 4 remains.
- 4 = 4, so take IV; nothing remains.
The pieces M + CM + XC + IV give MCMXCIV, exactly the breakdown this tool displays; the sum checks: 1000 + 900 + 90 + 4 = 1994.
Reading the other way, group MCMLXXXVII into additive chunks: M (1000) + CM (900) + L (50) + X (10) + X (10) + X (10) + V (5) + I (1) + I (1). The running sum: 1000 + 900 = 1900; 1900 + 50 = 1950; 1950 + 30 = 1980; 1980 + 7 = 1987. The Roman to Number tab returns 1987 and marks the input Valid: Yes.
Common Values at a Glance
The six subtractive pairs and the composite rows below show how numerals assemble from the base symbols.
| Number | Roman Numeral | Reading |
|---|---|---|
| 4 | IV | 5 − 1 |
| 9 | IX | 10 − 1 |
| 40 | XL | 50 − 10 |
| 90 | XC | 100 − 10 |
| 400 | CD | 500 − 100 |
| 900 | CM | 1000 − 100 |
| 1994 | MCMXCIV | 1000 + 900 + 90 + 4 |
| 1987 | MCMLXXXVII | 1000 + 900 + 50 + 10 + 10 + 10 + 5 + 1 + 1 |
| 2026 | MMXXVI | 1000 + 1000 + 10 + 10 + 5 + 1 |
| 3999 | MMMCMXCIX | 1000 + 1000 + 1000 + 900 + 90 + 9 |
How to Use
- Pick a direction with the tabs: Number to Roman or Roman to Number.
- For Number to Roman, type a whole number from 1 to 3999, such as 1994.
- For Roman to Number, type the numeral, such as MCMLXXXVII; lowercase is fine.
- Click Convert.
- Read the result: the numeral with its Breakdown, or the Arabic number with the Valid check.
Frequently Asked Questions
What is the largest number supported?
This tool supports numbers from 1 to 3999, the standard range for classic Roman numerals. The largest valid output is 3999, written MMMCMXCIX (1000 + 1000 + 1000 + 900 + 90 + 9). Numbers of 4000 and above require an overline notation that plain text cannot represent reliably.
Is lowercase input accepted?
Yes, lowercase letters are converted to uppercase automatically, so typing mcmxciv produces the same result as MCMXCIV: 1994. The input field also displays text in uppercase as you type.
How are subtractive pairs handled?
The converter uses all six standard pairs — IV for 4, IX for 9, XL for 40, XC for 90, CD for 400, and CM for 900 — and validates them in input. It writes 94 as XCIV (90 + 4) rather than LXXXXIIII, and flags a non-standard entry such as IL for 49; the correct form is XLIX (40 + 9).
Why is there no Roman numeral for zero?
The Roman system predates zero as a number, so it has no zero symbol; medieval scribes sometimes wrote N for the Latin nulla (nothing). Because zero cannot be expressed, this converter works with numbers from 1 to 3999.
What is the longest Roman numeral this converter can produce?
The longest valid numeral under 4000 is 3888: MMMDCCCLXXXVIII, 15 characters built from 3000 + 500 + 300 + 50 + 30 + 5 + 3. The largest value, 3999, needs only 9 characters (MMMCMXCIX) because subtractive pairs compress it.
How do I write the current year in Roman numerals?
Break the year into thousands, hundreds, tens, and ones. For 2026: 2000 is MM, 20 is XX, and 6 is VI, giving MMXXVI.
Why do some clocks show IIII instead of IV for 4?
Many clock and watch faces use IIII, a tradition called the clockmaker's four. Explanations range from visual symmetry with VIII opposite it on the dial to the form predating the subtractive convention. Standard modern notation uses IV, which this converter produces and accepts.