(assuming you need something like HEX→Dec)
- из + Genitive в + Accusative. For example, "из шестнадцатеричной в двоичную" = "from hexadecimal to binary"
Note that if you do not use a radio button list or a list of abbreviations, that requires oblique forms of words for "base 2", "base 8", "base10", "base 16". Though, they all will end in "-ой" for Genitive and "-ую" for Accusative (instead of "ая" in dictionary form). Again, this only applies if you use whole words and try to sound all natural, like writing it all in a single line or a sentence like "I want to convert 511 from decimal to binary". A simple interface like "511, from:Dec, to:HEX" may use just abbreviations or dictionary forms.
If you are planning to use Russian words for number systems (and do it grammatically) here's the way:
- look up the required word in the dictionary. Since "number system" is feminine in Russian, you would actually use "-ая" ending, not "-ый/-ий" (bin = двоичная, oct = восьмеричная, dec = десятичная, hex = шестнадцатеричная)
- replace -ая with -ой for the words in the first list
- replace -ая with -ую for the words in the second list
- makes sense to keep the two lists separate for all languages. Russian is not the only one where the forms are going to be different
- in Japanese people use postpositions, not prepositions, so you probably will need analogues like "source" and "result" rather than から and に