How do you convert 700 ml into a fraction?

A decimal number is simply a way of representing a number in such a way that the place value of each digit is ten times that of the digit to its right. It may or may not contain a fractional part. If not, the decimal representation does not require a decimal point. So the decimal for 700 ml is 700 ml! If you want it as a decimal fraction of some other quantity then you need to specify that second quantity.