Roman Arabic Numerals Converter for everybody. Converts Roman numbers to usual (Arabic) numbers and Arabic numbers to Roman. Conversion details can be shown for educational purpose. Conversion history can be saved into text-file or printed. The converter accepts numbers written in either Roman numerals or Arabic digits. Arabic digits are just usual digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 . They are called Arabic because they have Arabic origin. Roman numerals is a subset of Latin alphabet. Each letter in the subset have assigned numerical value: M=1000, D=500, C=100, L=50, X=10, V=5, I=1 . Numbers are formed as a sum of values represented by numerals. For example, MDCLXVI = 1000+500+100+50+10+5+1 = 1666 . Repeated numerals just add their value to the sum : MMDCCLXXVII = 1000+1000+500+100+100+50+10+10+5+1+1 = 2777 . M, C, X, and I can be repeated up to three times. D, L, and V cannot be repeated. Sometimes Romans used C, X, and I repeated four times, but as a rule Romans used "subtraction from the left" . That is Romans wrote IV = -1+5 = 4 instead of IIII = 1+1+1+1 = 4. Similarly XL = -10+50 = 40 instead of XXXX, CD = -100+500 = 400 instead of CCCC. Continuing this logic, we could write MA for MMMM, if A denoted 5000. But Romans did not have numerals greater than M. Thus M can be repeated any times. For example, MMMMMMDCCLXXVII = 6777. What about 20777? We have to repeat M twenty times. This is not convenient. Romans remedy this situation by multiplying numbers by 1000. For example, (XX) = 20000. Then 20777 = (XX)DCCLXXVII . Along with parentheses Romans used upper or lower bar for grouping numerals multiplied by 1000. Continuing this logic, we can apply parentheses twice to get millions. For example, ((XX)) = 20,000,000 . Although Roman did not have concepts of zero and negative numbers, the rule of "subtraction from the left" could lead to those concepts. For example, VX = -5+1 = 5, VVX = -5-5+1 = 0, VVIX = -5-5-1+10 = -1 . But Romans did not develop it. Note, that numerals subtracted from the left are less than the numeral on the right.