How do you write 0 in Roman numerals?

You do not – the Romans had no numeral for zero. Medieval writers occasionally used N (for nulla), but it was never part of the system, so the converter starts at 1.

What is the largest Roman numeral?

With the seven standard symbols the largest number is 3999 (MMMCMXCIX). Larger values needed an overline multiplying a symbol by 1,000, which is not used in modern writing.

Is IIII or IV correct for 4?

IV is the standard subtractive form used in writing and dates. IIII survives mainly on clock faces by tradition.

Why is 1999 MCMXCIX and not MIM?

Only I before V or X, X before L or C and C before D or M are valid subtractions. MIM would need I before M, so 1999 is M (1000) + CM (900) + XC (90) + IX (9).

Roman Numerals Converter – numbers to Roman numerals and back (1–3999)

How to use it

Type a number from 1 to 3999 in the left field, or a Roman numeral (upper or lower case) in the right one.
The other field fills in immediately and the result box shows the numeral broken into its symbol groups with their values.
If a numeral is malformed, the message names the rule it breaks and offers the standard spelling as a one-click fix.
Copy the numeral or the number, or click a year chip to see a familiar date.

Example

1994 breaks into 1000 + 900 + 90 + 4 = M + CM + XC + IV = MCMXCIV. Reading it back: M (1000), then C before M means 1000 − 100 = 900, X before C means 100 − 10 = 90, and I before V means 5 − 1 = 4. Typing IC for 99 is flagged, because I may only precede V or X; the correct form is XCIX (90 + 9).

Rules of standard Roman numerals

Symbol	Value	Usage
I	1	repeats up to three times: II = 2, III = 3
V	5	never repeated; IV = 4
X	10	XX = 20, XXX = 30; IX = 9
L	50	never repeated; XL = 40
C	100	CC = 200, CCC = 300; XC = 90
D	500	never repeated; CD = 400
M	1,000	MM = 2000, MMM = 3000; CM = 900

Writing a number: take the thousands, hundreds, tens and units separately and spell each digit with its own symbols (1–3 additive, 4 and 9 subtractive, 5–8 as V/L/D plus additive marks). Reading a numeral: add the symbols from left to right, subtracting any symbol that stands before a larger one.

digit  1  2   3    4   5  6   7    8     9
units  I  II  III  IV  V  VI  VII  VIII  IX
tens   X  XX  XXX  XL  L  LX  LXX  LXXX  XC
100s   C  CC  CCC  CD  D  DC  DCC  DCCC  CM

The converter accepts lower case, spaces, a trailing dot or ordinal suffix (“XX.”, “XIVth”) and the Unicode Roman numeral characters (Ⅻ). Larger values used a bar (vinculum) over a symbol to multiply it by 1,000 (V̄ = 5,000); that notation is rare today and not supported here.

Common years

Year	Roman numeral	Note
1776	MDCCLXXVI	US Declaration of Independence
1945	MCMXLV	end of World War II
1969	MCMLXIX	Moon landing
1999	MCMXCIX	last year of the 1900s
2000	MM	the millennium
2024	MMXXIV
2025	MMXXV
2026	MMXXVI

Sources: Wikipedia – Roman numerals, Encyclopaedia Britannica – Roman numeral.

Why clocks show IIII

Many clock faces use IIII instead of IV for 4. The usual explanations are visual balance against VIII on the opposite side and the four-symbol groups (I, II, III, IIII; V, VI, VII, VIII; IX, X, XI, XII) that let a founder cast the numerals from fewer moulds. In text, dates, chapter numbers and names of monarchs the subtractive IV is the standard form, which is what this converter produces.

Questions

How do you write 0 in Roman numerals?: You do not – the Romans had no numeral for zero. Medieval writers occasionally used N (for nulla), but it was never part of the system, so the converter starts at 1.
What is the largest Roman numeral?: With the seven standard symbols the largest number is 3999 (MMMCMXCIX). Larger values needed an overline multiplying a symbol by 1,000, which is not used in modern writing.
Is IIII or IV correct for 4?: IV is the standard subtractive form used in writing and dates. IIII survives mainly on clock faces by tradition.
Why is 1999 MCMXCIX and not MIM?: Only I before V or X, X before L or C and C before D or M are valid subtractions. MIM would need I before M, so 1999 is M (1000) + CM (900) + XC (90) + IX (9).