How this calculator works
Modern Roman notation combines I, V, X, L, C, D and M. Symbols usually add from largest to smallest, with IV, IX, XL, XC, CD and CM providing the standard subtractive pairs. Encoding chooses each largest available symbol or pair. Decoding first checks canonical ordering and repetition, then subtracts a symbol only when a larger one follows. The supported range is 1 through 3999; zero, negatives, fractions and overbar notation are outside this convention.
Formula
I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Standard subtraction pairs are IV=4, IX=9, XL=40, XC=90, CD=400, CM=900.
Worked example
1994 separates into 1000 + 900 + 90 + 4, written M + CM + XC + IV = MCMXCIV. XLIX is 40 + 9 = 49.
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Frequently asked questions
Why is IIII rejected?
Some clocks and historical texts use IIII. This tool validates the modern canonical form IV so each accepted integer has one representation.
Can Roman numerals express zero?
There is no zero symbol in the convention used here. Enter a whole number from 1 to 3999.
Does lowercase input work?
Yes. Lowercase Roman letters are normalised to uppercase before validation.