Roman numeral converter

Number

Or a numeral

Roman numeral —

Value —

Note Roman numerals run from 1 to 3999 — there is no zero

Local · standard subtractive form, 1–3999

Fill in either box. Numbers become numerals in standard subtractive form — 4 is IV, not IIII — and numerals are read back to numbers, with anything malformed rejected rather than guessed at.

How to convert Roman numerals

1 Type a number between 1 and 3999, or type a numeral into the second box.

2 Read the conversion. The seven symbols are listed underneath for reference.

3 If a numeral is rejected, it is not in standard form — usually a repeated V, L or D, or too many of one symbol in a row.

Two rules do most of the work. A smaller symbol before a larger one subtracts, so IV is four and IX is nine; only I, X and C can subtract, and only from the next two symbols up, which is why 99 is XCIX and never IC. And no symbol repeats more than three times, which is why 4 is IV rather than IIII — the IIII you see on clock faces is a deliberate stylistic exception and not standard. The system also has no zero and no way to write a negative number, and it stops at 3999 because 4000 would need four M’s. Larger numbers used an overbar meaning "times a thousand", which is not what anyone converting a date needs.

Questions

Why is 4 written IV and not IIII? −

Standard form does not repeat a symbol more than three times. The IIII on clock faces is a stylistic convention, not correct notation.

What is the largest Roman numeral? +

Is there a Roman numeral for zero? +

Why is 99 XCIX rather than IC? +

What year is MMXXVI? +

How do I write a date? +

Sources

Encyclopaedia Britannica — Roman numeral

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