Roman Numeral Converter
Numbers to Roman numerals and back, with the working shown and the subtractive rules explained.
In short
Roman numerals use I, V, X, L, C, D and M, written largest to smallest and added. A smaller symbol before a larger one is subtracted: IV is 4 and CM is 900. Only I, X and C may be subtracted.
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The seven symbols
Everything in the system is built from I (1), V (5), X (10), L (50), C (100), D (500) and M (1000). Numerals are written largest to smallest and added together: MMXXVI is 1000 + 1000 + 10 + 10 + 5 + 1 = 2026.
The subtractive rule, and its limits
A smaller symbol placed before a larger one is subtracted rather than added. IV is 4, IX is 9, XL is 40, CM is 900.
The rule is narrower than most people assume. Only three symbols may be subtracted, and only from the next two sizes up:
- I before V or X, IV (4), IX (9)
- X before L or C, XL (40), XC (90)
- C before D or M, CD (400), CM (900)
So IL for 49 is invalid. It must be XLIX. IC for 99 is invalid. XCIX. And V, L and D are never subtracted at all, because each already represents a "half step" and doubling down would be ambiguous.
Converting by hand
Work through the place values from largest to smallest. For 2026:
- 2000 → MM
- 0 hundreds → nothing
- 20 → XX
- 6 → VI
Giving MMXXVI. Going the other way, read left to right and subtract whenever a symbol is smaller than the one following it.
Numbers above 3,999
Classical notation runs out at 3,999 (MMMCMXCIX), because four M's in a row breaks the rule against repeating a symbol more than three times.
Beyond that, a vinculum: a bar above the numeral. Multiplies it by 1,000. V̄ is 5,000; X̄ is 10,000; M̄ is 1,000,000. Because the bar is hard to type and renders inconsistently, parentheses are a common substitute: (V) for 5,000. Both are offered here.
Why IIII appears on clocks
Most analogue clock faces using Roman numerals show IIII rather than IV for four. The usual explanations are visual balance, IIII on the left mirrors VIII on the right. And the practical matter that a clockmaker casting numerals needs a tidy count of each symbol. Some also cite avoiding IV as the first letters of IVPITER. Big Ben is the well-known exception, using IV.
Where you'll still meet them
- Monarchs and popes: Elizabeth II, Louis XIV.
- Book front matter: prefaces numbered i, ii, iii before page 1.
- Film copyright dates: historically used to make a film's age less obvious.
- Super Bowls: with the notable exception of Super Bowl 50, since "L" alone looked wrong.
- Clock faces, cornerstones and monuments.
- Outlines: I, II, III for top-level headings.
- Tattoos: usually dates, which is a good reason to check the conversion twice.
Why the system was abandoned for arithmetic
There is no zero and no place value, which makes written calculation extremely awkward. Try long division in Roman numerals. Medieval Europe did arithmetic on a counting board and recorded only the result in numerals. Hindu-Arabic numerals arrived with both a zero and positional notation, and by the 16th century they had largely won. Roman numerals survive because they look formal, not because they're useful.
Frequently asked questions
What are the Roman numeral symbols?
I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000. Everything else is built from these seven by addition and the subtractive rule.
Why is 4 written IV and not IIII?
The subtractive rule: a smaller symbol before a larger one is subtracted. IV is 5−1 = 4, IX is 10−1 = 9. Only I, X and C may be subtracted, and only from the next two larger symbols. So IV and IX are valid, but IL and IC are not. Clock faces are the famous exception, often using IIII for 4 purely for visual balance.
How do I write large numbers?
A bar above a numeral, the vinculum. Multiplies it by 1,000. So V̄ is 5,000 and X̄ is 10,000. Since the bar is awkward to type, this tool also offers the common parenthesis convention, (V) for 5,000, and will convert up to 3,999,999.
Is there a zero in Roman numerals?
No. The system has no symbol for zero and no way to express negative numbers or fractions of the decimal sort. Medieval scribes occasionally wrote nulla when they needed the concept. This absence is a large part of why the system was eventually replaced for arithmetic.
How do I write a date in Roman numerals?
Convert each part separately. 14 March 2026 becomes XIV·III·MMXXVI. Tattoos and monuments usually run day·month·year, though building cornerstones often show the year alone. Check the order before committing it permanently to anything.