Roman Numeral Converter
Convert numbers to Roman numerals (1–3999) and Roman numerals back to numbers.
Written by Anil Gautam · Updated
How do you write a number in Roman numerals?
Seven letters carry values: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500 and M = 1000. The converter works from the largest value down, writing the biggest symbol that fits as many times as it fits before moving to the next. Six two-letter pairs handle the 4s and 9s by subtraction: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900).
Take 1994. It splits into 1000 + 900 + 90 + 4, written M, CM, XC and IV, so the result is MCMXCIV. The default value, 2026, is MM + XX + VI = MMXXVI, and 1947 gives MCMXLVII. Reading the other way, add the letters from left to right and subtract any letter that stands before a larger one. In XLV, X comes before L, so the value is 50 - 10 + 5 = 45.
Why does the tool reject IIII or IC?
Roman to number mode accepts only the standard modern form. After adding up your letters, the tool converts the total back to Roman numerals and compares the two spellings, and any difference produces Not a valid Roman numeral. IIII adds up to 4, whose standard form is IV. IC and IM look like 99 and 999, yet only I, X and C can be subtracted, and only from the next two larger symbols, so the accepted forms are XCIX and CMXCIX. V, L and D never repeat and never subtract, which rules out VV, VX and DD.
Clock faces often use IIII, and old inscriptions contain other variants, so the tool will reject some numerals you can find on real objects. Lowercase letters and spaces are fine: m cm xc iv reads as 1994. In number to Roman mode, enter a whole number from 1 to 3999. Zero, negative numbers and fractions such as 12.5 return the error message, because the standard system has no symbols for them.
Where do Roman numerals still appear?
Film and television credits often give the copyright year this way, so MCMXCIX on a closing card means 1999. Book front matter is numbered with lowercase numerals such as iv and xii, and names such as Elizabeth II use them for order. For writing an amount in words on a cheque or invoice, use the Number to Words Converter, and for binary or hexadecimal, the Base Converter.