Free Roman Numeral Converter Online

Convert numbers to Roman numerals and back, instantly. Auto-detects direction, validates non-standard input, and supports 1 to 3,999,999 using vinculum (overline) notation for large values.

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Enter a number or a Roman numeral

Result

Step-by-step breakdown

Symbol reference

Symbol	Value
I	1
V	5
X	10
L	50
C	100
D	500
M	1000

Numbers 1–20

Roman numeral rules

Symbols are written largest to smallest, left to right.
If a smaller numeral appears before a larger one, subtract it (IV = 4, IX = 9).
A symbol cannot be repeated more than 3 times in a row (4 is IV, not IIII).
Only I, X, and C can be used as subtractive prefixes.
An overline (vinculum) multiplies a numeral by 1,000 - V̅ = 5,000, X̅ = 10,000.

Guide

How Roman numerals work

Roman numerals build numbers from seven letters: I (1), V (5), X (10), L (50), C (100), D (500), and M (1000). You read them by adding values from largest to smallest, so MMXXIV is 1000 + 1000 + 10 + 10 + 4 = 2024 (the final IV is the subtractive form of 4). The converter handles both directions automatically and validates input, so non-standard forms are caught.

The subtractive rule (why 4 is IV, not IIII)

To avoid four identical letters in a row, Roman numerals use a subtractive rule: when a smaller value sits before a larger one, you subtract it. So 4 is IV (5 minus 1), 9 is IX (10 minus 1), 40 is XL, 90 is XC, 400 is CD, and 900 is CM. Only certain pairs are allowed (I before V or X, X before L or C, C before D or M), which keeps the system unambiguous.

Reading years

Years are the most common real-world Roman numerals, seen on buildings, films, and copyright lines. For example, MCMXCIV breaks down as M (1000) + CM (900) + XC (90) + IV (4) = 1994. To write the current year, enter it above and the tool builds the numeral for you, applying the subtractive rule correctly.

How large can Roman numerals go?

In standard notation, the largest value is 3,999 (MMMCMXCIX), because there is no single symbol beyond M. To represent larger numbers, the system uses a vinculum, an overline that multiplies a numeral by 1,000. This tool supports vinculum notation up to 3,999,999, so you can convert numbers far beyond the classic limit.

Last updated: July 2026

Frequently Asked Questions

How do I convert a number to Roman numerals?

Break the number into thousands, hundreds, tens, and ones, then convert each part using the standard symbols (I, V, X, L, C, D, M), applying subtractive notation where needed (like IV for 4, IX for 9). This tool does the conversion instantly.

What is the largest number you can write in Roman numerals?

Using standard notation, 3,999 (MMMCMXCIX) is the practical limit since there’s no single symbol for 5,000 in common use. Extended notation using overlines (a vinculum) multiplies a numeral by 1,000, allowing values up to 3,999,999.

Why is 4 written as IV instead of IIII?

Roman numeral rules limit any symbol to a maximum of 3 repetitions in a row. Subtractive notation (IV) was adopted to avoid four identical symbols in sequence, though IIII does appear historically on some clock faces.

What year is MCMXCIV?

MCMXCIV represents 1994. Breaking it down: M (1000) + CM (900) + XC (90) + IV (4) = 1994.

How do I write the current year in Roman numerals?

Enter the current year into the converter above for an instant result. Roman numeral years are commonly used in movie copyright notices, building cornerstones, and formal documents.