Roman Numeral Converter

How the Roman numeral converter turns a number into numerals

Turning a number into Roman numerals, or reading one back the other way, always comes down to the same seven symbols and a handful of rules, no matter how large the number is. Knowing how to write Roman numerals starts with the seven roman numeral symbols themselves and the roman numeral rules for combining them. Roman numerals are built from seven symbols, each with a fixed value: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500, and M is 1000. Converting a number to Roman numerals uses a greedy-subtraction algorithm: starting from the largest available value, repeatedly subtract it from the number and append its symbol, for as long as it still fits, then move on to the next-largest value. Some values are not single symbols but standard two-letter combinations that represent subtraction, such as CM for 900 (1000 minus 100) or XC for 90 (100 minus 10), which exist specifically so a value like 900 is not written as a long run of hundreds symbols.

Worked example: 1994. The full list of values, from largest to smallest, is 1000 (M), 900 (CM), 500 (D), 400 (CD), 100 (C), 90 (XC), 50 (L), 40 (XL), 10 (X), 9 (IX), 5 (V), 4 (IV), and 1 (I). Starting from 1994: 1000 fits once, leaving 994 and appending M. 900 fits once, leaving 94 and appending CM. 500, 400, and 100 do not fit into 94. 90 fits once, leaving 4 and appending XC. 50, 40, 10, 9, and 5 do not fit into 4. 4 fits once, leaving 0 and appending IV. The result, read in the order the symbols were appended, is MCMXCIV. Notice this single example uses three different subtractive pairs, CM, XC, and IV, which is exactly why 1994 is such a commonly cited example when explaining the algorithm.

How parsing works in reverse

To convert Roman numerals to numbers, or convert number to Roman numerals going the other way, the two directions on this page share the same underlying symbol table, just applied in opposite order. Converting a Roman numeral back to a number reads the symbols from left to right and applies one rule at each position: compare the current symbol's value to the value of the symbol immediately after it. If the current symbol's value is smaller than the next one's, subtract it instead of adding it; otherwise, add it as usual. Reading MCMXCIV this way: M (1000) is followed by C (100), which is not larger, so add 1000. C (100) is followed by M (1000), which is larger, so subtract 100. M (1000) is followed by X (10), not larger, so add 1000. X (10) is followed by C (100), larger, so subtract 10. C (100) is followed by I (1), not larger, so add 100. I (1) is followed by V (5), larger, so subtract 1. V (5) is the last symbol, so add 5. Adding these together: 1000 minus 100 plus 1000 minus 10 plus 100 minus 1 plus 5 equals 1994, matching the original number from the example above.

A naive version of this left-to-right rule would still add up something like "IIII" as 1 + 1 + 1 + 1 = 4, or accept nonsense strings such as "VX" as 5 (reading V, then subtracting nothing meaningful) without flagging that they are not real Roman numerals. To avoid that, this converter takes the number it computes and converts it back to a Roman numeral using the same greedy-subtraction algorithm described above, then checks that the result matches the original input exactly. "IIII" converts to the number 4, but 4 converted back to a Roman numeral is "IV", not "IIII", so the round trip fails and the input is rejected. This is why "IIII" is not considered valid modern Roman numeral notation: subtractive notation like "IV" has been the standard way to write 4 for centuries, even though repeated-symbol forms like "IIII" occasionally still appear in decorative contexts such as some clock faces.

Quick reference: symbols and subtractive pairs

Use this as a quick roman numeral chart, or roman numeral lookup, whenever you just need the symbol values rather than the full converter above. Seven symbols carry a fixed value: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500, and M is 1000. Exactly six subtractive pairs cover every place a smaller symbol appears immediately before a larger one: IV (4), IX (9), XL (40), XC (90), CD (400), and CM (900). Every valid Roman numeral, no matter how long, is built from nothing more than these seven symbols and six pairs, combined by reading from the largest value down to the smallest.

Worked example: converting the current year, 2026

Turning a year into Roman numerals is one of the most common reasons people reach for a year to Roman numerals converter, whether for a birth year in Roman numerals on a gift or tattoo, or a date to Roman numerals converter for a wedding invitation or building cornerstone. Applying the same greedy-subtraction steps used above to 2026: 1000 fits twice, leaving 26 and appending MM. None of 900, 500, 400, or 100 fit into 26. 90, 50, and 40 do not fit either. 10 fits twice, leaving 6 and appending XX. 9 and 5 do not both fit; 5 fits once, leaving 1 and appending V. 4 does not fit, but 1 does, appending I. Reading the appended symbols in order gives MMXXVI, the Roman numeral for 2026.

More conversions at a glance

A few more values worth having on hand: 4 is IV, 9 is IX, 40 is XL, 90 is XC, and 88 is LXXXVIII, eight symbols long since 88 has no subtractive shortcut beyond the XC and XL already used to build its tens, and 500 is simply D. Two more that come up constantly: LX is 60, built from L (50) plus X (10) with no subtraction needed at all, and XIV Roman numerals give 14, combining X (10) with IV (4). The Roman numeral 9 is written IX rather than four I's in a row, a pattern many people look up specifically as ix in roman numerals, and the same subtractive idea is why 14 in Roman numerals is XIV rather than a longer string of repeated symbols. Every one of these leans on the L roman letter or another of the seven base symbols always meaning the same fixed value wherever it appears, 50 for L, no matter how long the full numeral around it gets.

Quick lookups for the numbers people ask about most

Two short lookups sit side by side: common numbers and years written as Roman numerals on the left, and a few numerals read back into numbers on the right.

Tips for entering values

Whether you think of this as a roman numeral calculator or a roman numeral translator online, the same input rules apply on both tabs. Case never matters: mcmxciv, McmXciv, and MCMXCIV are all read identically, since input is converted to uppercase automatically before parsing. Extra spaces typed around a Roman numeral are trimmed automatically as well. On the "Number to Roman numeral" side, only whole numbers from 1 to 3999 are accepted, so a decimal like 4.5 or a number like 4000 returns a message explaining why, rather than an incorrect or partial numeral.

Common data-entry patterns that get rejected, and why

A few Roman numeral strings look plausible but fail the validity check this converter runs, and knowing the pattern behind a rejection avoids repeated retyping. A numeral with four or more of the same symbol in a row, such as IIII or XXXX, is rejected because standard notation never repeats a symbol more than three times; the correct forms are IV and XL. A numeral that repeats V, L, or D, such as VV or LL, is rejected because those three symbols are never repeated at all, since a repeated one always has a shorter standard form (VV is just X). A numeral built around a subtractive pair that is not one of the six listed above, such as IC in an attempt to mean 99, is rejected because I is only ever allowed to subtract from V or X, never from C; 99 is correctly written XCIX (90 plus 9) instead.