Type a number or type Roman numerals — it works out which you meant and converts either way, showing the breakdown and flagging invalid forms.
Type 1994 to get MCMXCIV, or type MCMXCIV to get 1994. Whole numbers from 1 to 3999.
Roman numerals
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Roman—
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Read as a year—
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The seven symbols
Symbol
Value
Origin of the letter
I
1
A single tally mark
V
5
An open hand, five fingers
X
10
Two hands crossed
L
50
Adapted from an early Greek letter
C
100
Centum, Latin for hundred
D
500
Half of an older symbol for 1000
M
1000
Mille, Latin for thousand
How the rules work
Write the symbols from largest to smallest and add them up: MDCLXVI is 1000 + 500 + 100 + 50 + 10 + 5 + 1 = 1666. Where a smaller symbol appears immediately before a larger one, it is subtracted instead: IV is 4, IX is 9, XL is 40, XC is 90, CD is 400, CM is 900.
Only six subtractive pairs are valid, and only I, X and C can ever be subtracted. You cannot write IL for 49 — it is XLIX. You cannot write VL, IC or XD at all. Nor can a symbol repeat more than three times in a row, which is why 4 is IV and not IIII, and why 3999 (MMMCMXCIX) is the highest number the standard system can express.
Working through 1994
M = 1000, CM = 900, XC = 90, IV = 4. Add them: 1000 + 900 + 90 + 4 = 1994, written MCMXCIV.
Look at almost any traditional clock and four is IIII, not IV — a form usually called the "clockmaker's four". The most credible explanation is visual balance: IIII on the left mirrors the weight of VIII on the right, and it also means the dial uses exactly twenty I, four V and four X, which suits casting the numerals as a set. Big Ben is the famous exception, using IV. Either way, this converter produces the standard IV.
Where you still meet them
Film and television copyright dates, monarchs and popes (Elizabeth II, Louis XIV), Super Bowls, book prefaces and chapter numbers, building cornerstones, watch faces, and outline numbering all still use Roman numerals. They persist because they read as formal and timeless, not because they are useful for arithmetic — try multiplying MCMXCIV by VII and the reason positional notation replaced them becomes obvious immediately.
Beyond 3999
Standard Roman numerals stop at MMMCMXCIX, since there is no symbol above M and you may not write four in a row. Larger values used the vinculum — an overline multiplying a numeral by a thousand, so V̄ meant 5,000. That notation is rare, inconsistently applied, and not supported here.
MMXXVI — that is M (1000) + M (1000) + X (10) + X (10) + V (5) + I (1). Years in the 2000s all start MM, followed by the rest of the number.
What is MCMXCIV?
1994. It breaks down as M (1000) + CM (900) + XC (90) + IV (4). It is a favourite example because it uses three different subtractive pairs in one number.
Why is 4 written IV and not IIII?
Because no symbol may repeat more than three times, so IIII is invalid in standard notation and 4 is written as one less than five. Clock faces are the well-known exception, where IIII is used for visual balance against VIII.
What is the largest Roman numeral?
MMMCMXCIX, or 3999. There is no symbol larger than M and you cannot write MMMM, so the standard system stops there. Larger numbers historically used an overline to multiply by a thousand.
Is there a zero in Roman numerals?
No. The system has no symbol for zero and no concept of place value, which is exactly why arithmetic with it is so awkward and why Hindu-Arabic numerals displaced it for calculation.