Roman Numeral Converter & Decoder (1–3999)
Convert or validate modern conventional Roman numerals, see the working, and practise without uploading your entries.
Convert one value
Private by default: your entry stays in this browser tab. It is not saved, placed in the URL, or sent for conversion.
Use digits only for 1–3999, or the letters I, V, X, L, C, D and M.
Check a list
Up to 200 non-empty rows are processed locally. Invalid rows are kept visible instead of being silently skipped.
Practice quiz
Answer at your own pace. The next question appears only when you choose it, so feedback is not removed by a timer.
Roman Numeral Reference
| Roman | Value | Rule |
|---|---|---|
| I | 1 | Base unit |
| IV | 4 | Subtractive: 5 - 1 |
| V | 5 | Base symbol |
| IX | 9 | Subtractive: 10 - 1 |
| X | 10 | Base symbol |
| XL | 40 | Subtractive: 50 - 10 |
| L | 50 | Base symbol |
| XC | 90 | Subtractive: 100 - 10 |
| C | 100 | Base symbol |
| CD | 400 | Subtractive: 500 - 100 |
| D | 500 | Base symbol |
| CM | 900 | Subtractive: 1000 - 100 |
| M | 1000 | Base symbol |
How to convert numbers to Roman numerals
Roman numerals build each value from seven letters — I (1), V (5), X (10), L (50), C (100), D (500) and M (1000) — written from largest to smallest and added together. To convert a decimal number by hand, break it into thousands, hundreds, tens and units, then swap each part for its symbol.
- Take the biggest place value first. For 2024, start with 2000 = MM.
- Convert the next place down: 20 = XX, then 4 = IV (subtractive form of 5−1).
- Join the parts in order: MM + XX + IV = MMXXIV.
In the modern convention used by this tool, I, X, C and M can repeat up to three times, while V, L and D do not repeat. The accepted subtractive pairs are IV, IX, XL, XC, CD and CM. Historical inscriptions and some clock faces use variants such as IIII; this checker deliberately reports those as non-canonical.
How the converter checks Roman numerals
This page accepts one clearly stated modern convention from 1 to 3999. Roman numeral usage has varied across periods and contexts, so “invalid” here means “outside this converter’s convention,” not “never used historically.”
- Decimal input is converted with the standard M, CM, D, CD, C, XC, L, XL, X, IX, V, IV, and I sequence.
- Roman input is parsed, then converted back to Roman to confirm the notation is canonical.
- Batch mode uses the same validator for every line and reports bad rows rather than silently dropping them.
- Zero, negative numbers, fractions, overlines and historical variants are outside this tool’s scope.