Roman Numeral Converter
Convert numbers to Roman numerals and Roman numerals back to numbers, with the subtractive rules explained and each symbol broken down.
How to use this calculator
- 1Choose which direction you are converting.
- 2Enter a whole number from 1 to 3999, or a Roman numeral using only I, V, X, L, C, D, and M.
- 3The symbol breakdown shows how the numeral is built place value by place value.
How it works
Roman numeral rules
I = 1 V = 5 X = 10 L = 50 C = 100 D = 500 M = 1000 Repeat a symbol up to three times to add: III = 3 Place a smaller symbol before a larger one to subtract: IV = 4 Only IV, IX, XL, XC, CD, CM are valid subtractive pairs
Roman numerals are additive by default — you write symbols largest to smallest and add them up. The subtractive pairs exist to avoid four repeats: 4 is IV rather than IIII, and 9 is IX rather than VIIII. Only I, X, and C can be subtracted, and each may only precede the next two larger symbols, which is why IC is not a valid way to write 99 (it is XCIX).
Worked example
2026 breaks into 2000 + 20 + 6. Two thousands give MM, two tens give XX, five plus one gives VI — so 2026 is MMXXVI. Reading backwards, MMXXVI sums to 1000 + 1000 + 10 + 10 + 5 + 1 = 2026.
Roman Numeral Converter: the complete guide
How to read a Roman numeral
Work left to right and compare each symbol with the one after it. If it is larger than or equal to the next, add it. If it is smaller, subtract it. MCMXCIV reads as M (1000), then C before M meaning −100 +1000 = 900, then X before C meaning 90, then I before V meaning 4 — giving 1994.
Because the subtractive pairs are always exactly two symbols, you never need to look more than one symbol ahead. That is what makes the system readable at all despite having no positional notation.
The rules that make a numeral valid
Only I, X, and C may be subtracted, and only from the next two larger symbols. That gives exactly six legal subtractive pairs: IV, IX, XL, XC, CD, CM. V, L, and D are never subtracted, and never repeated — VV would simply be X.
A symbol repeats at most three times in a row. Four of anything triggers the subtractive form instead. This is why IIII is non-standard, even though clock faces have used it for centuries for visual balance against the VIII opposite.
This calculator enforces canonical form by converting your input back to a numeral and checking it matches. IC, VX, and IIII are all rejected rather than silently interpreted, which is what you want when checking a copyright date or a monument inscription.
Why there is no zero and no numbers past 3999
Roman numerals are a tally system, not a positional one. Each symbol carries its own fixed value regardless of where it sits, so there is no empty place to mark and therefore no need for a zero. That absence made arithmetic painful and is a large part of why Hindu-Arabic numerals displaced them for calculation.
M is the largest standard symbol, and no more than three may repeat, so MMMCMXCIX (3999) is the ceiling. The Romans extended the system with a vinculum — a bar over a symbol multiplying it by 1,000, so V̄ meant 5,000 — but overbars do not survive plain text, which is why virtually every converter stops at 3999.
Where you still see them
Film copyright dates, book chapter numbers, monarch and pope regnal numbers, Super Bowl editions, clock faces, and the outline levels of formal documents. In each case the numerals signal formality or tradition rather than serving any computational purpose.
The most practical use today is decoding a copyright line at the end of a film: MCMLXXXIV is 1984, MMXIV is 2014. Paste it into the converter above rather than counting Xs.
Frequently asked questions
What is 2026 in Roman numerals?
MMXXVI. Two Ms give 2000, two Xs give 20, and VI gives 6. Reading it back: 1000 + 1000 + 10 + 10 + 5 + 1 = 2026.
Why is 4 written as IV and not IIII?
Standard form limits any symbol to three consecutive repeats, so four ones must use the subtractive pair IV — one before five, meaning five minus one. Clock faces often use IIII anyway, purely for visual symmetry with the VIII on the opposite side.
Is IC a valid way to write 99?
No. Subtraction is only allowed from the next two larger symbols, so I may precede only V and X. 99 is XCIX — ninety (XC) followed by nine (IX). This calculator rejects IC rather than guessing what you meant.
How did Romans write numbers larger than 3999?
With a vinculum: a horizontal bar over a symbol multiplied it by 1,000, so V̄ was 5,000 and X̄ was 10,000. The notation cannot be typed reliably in plain text, which is why standard converters cap at 3999.