Roman numeral converter and checker
Turn a number into a Roman numeral, or a Roman numeral back into a number, for any whole number 1 to 3,999 (the range covered by the modern classroom convention used here). It checks your input both ways and tells you if a numeral is not valid. Every answer is computed in code, so it is never wrong. Free, no sign-up.
Number to Roman numeral
Result appears here.
Roman numeral to number
Result appears here.
The seven symbols
Subtractive pairs
A smaller symbol before a bigger one means subtract.
Standard Roman numerals have no zero placeholder, but Romans could still record fractions, often in twelfths.
How Roman numerals work
The modern Roman numeral convention taught in schools builds numbers from seven letters: I (1), V (5), X (10), L (50), C (100), D (500) and M (1000). You add symbols from largest to smallest, so 2026 is MMXXVI (1000 + 1000 + 10 + 10 + 5 + 1).
Its main twist is subtraction: a smaller symbol placed before a bigger one is subtracted. That is why 4 is IV (5 minus 1) and 40 is XL (50 minus 10). Only six pairs are allowed, IV, IX, XL, XC, CD and CM, and a symbol is never repeated more than three times in a row.
Common mistakes the checker catches
- IIII for 4, it should be IV (four of a symbol in a row is not allowed).
- VV for 10, V, L and D are never doubled; use X.
- IC for 99, you can only subtract from the next one or two sizes up, so 99 is XCIX.
- IL for 49, the same rule; 49 is XLIX.
Numbers beyond 3,999
This converter covers 1 to 3,999, the range supported by its modern classroom rules using the seven familiar symbols. Historical Roman notation was less uniform: extra symbols were used for some larger values, and overlines could multiply a value by 1,000 in later conventions. We show the overline as a useful reference, not as the only method Romans ever used or something students must type into the converter.
| Symbol | Value | With a bar (×1,000) |
|---|---|---|
| I | 1 | I(1,000) |
| V | 5 | V(5,000) |
| X | 10 | X(10,000) |
| L | 50 | L(50,000) |
| C | 100 | C(100,000) |
| D | 500 | D(500,000) |
| M | 1,000 | M(1,000,000) |
Who were the Romans?
These numerals come from ancient Rome. Rome began almost 2,800 years ago as a small town in Italy, and over time it grew into one of the largest empires the world has ever seen, stretching all the way around the Mediterranean Sea. At its height, tens of millions of people lived under Roman rule, from Britain in the north to Egypt in the south.
According to Roman tradition, Rome was first ruled by kings. It became a republic around 509 BC, governed through elected offices and a senate, although political power was far from equally shared. In 27 BC Augustus became its first emperor. Everyday life mixed the familiar and the strange: families, schools and markets, but also enormous public baths, chariot races, and gladiator games in arenas like the Colosseum.
The Romans were brilliant builders and organisers, and we still use many of their ideas:
- Roads and aqueducts carefully engineered for terrain, often in long straight sections, with some structures still standing today.
- Concrete strong enough to build domes and bridges that have lasted 2,000 years.
- Latin, Rome's principal language, which grew into Spanish, French, Italian and more, and shaped English; the empire itself was multilingual.
- Written laws that many modern legal systems are still based on.
- The Julian calendar, which strongly shaped the Gregorian calendar used internationally today, and these numerals for labels and dates.
Roman numeral notation is non-positional, while calculations were commonly performed with counting boards or abaci. The notation is awkward for long written sums (try adding MCMXLVII and DCCXXIX in your head), and positional Hindu-Arabic numerals later became standard in Europe. Roman numerals never disappeared, and reading them remains a useful skill.
Teachers: this pairs well with a history unit on ancient Rome and a maths lesson on place value and subtraction. Print a Roman numerals worksheet to practise.
Accuracy and sources
These references explain why the historical wording above distinguishes modern classroom rules from the varied notation Romans actually used.
- University of St Andrews — Roman fractions documents the Roman system of named fractions based chiefly on twelfths, so “no values below one” would be inaccurate.
- Metropolitan Museum of Art — The Roman Republic gives the conventional sequence from kings to the Republic and then Augustus.
- Unicode Standard — ancient and archaic Roman numerals records additional symbols for values such as 5,000 and 10,000, showing why 3,999 is a converter convention rather than a historical maximum.
- US National Institute of Standards and Technology — Julian and Gregorian calendars explains that the Gregorian calendar corrected and developed the earlier Julian system.
- University of Notre Dame — “All roads lead to Rome” traces the familiar wording to a medieval text from 1175 rather than to an ancient Roman saying.
Where you still see them
Clock faces, book chapters, film credits and copyright years, the Super Bowl, and the names of monarchs and popes (Elizabeth II, Louis XIV). Reading them is a genuinely useful everyday skill, and a friendly way to practise place value and mental subtraction.
Clock faces
Book chapters
Film credits
Monarchs & popes
Book chapter numbers, quick reference
The most common everyday use: numbering chapters, front-matter pages, or a book's edition. Here are the first 20, or type any chapter number into the converter above.
Common questions
- What is the largest Roman numeral?
- This converter's modern classroom convention covers 1 to 3999, with 3999 written MMMCMXCIX. Historically there was no single universal maximum: Romans also used extra symbols and several conventions for larger values, including overlines in some periods.
- Why is 4 written IV and not IIII?
- In the modern classroom convention used by this converter, a symbol is not repeated four times. A smaller symbol before a larger one can mean subtraction, so 4 is IV and 9 is IX. Historical inscriptions varied, and IIII remains traditional on many clock faces.
- Is there a zero in Roman numerals?
- Standard Roman numeral notation has no zero placeholder and is not designed for negative numbers. That does not mean Romans could not describe nothing or values below one: they used words for absence and a system of fractions, often based on twelfths.
Want practice on paper? Print a free Roman numerals worksheet with a computed answer key, or see more free classroom tools.