Convert decimal to fraction of an inch

I am puzzled by this small problem I used to know how to do it but I forgot. For example I have 2.12 inch. I aready know that the number 2 has a value of 2 inches but how about the decimal part? How can I find the nearest fraction of an in. (1/4 of an inch, 1/16 of an in, 1/5 of an inch and so on) to the unity of inch. For this problem I aready know that the answer is 2.12 in. rounded up is close to **2 1/8 in**. How about for any other whole number with a decimal or forget the whole number and please help me to convet from decimal to the nearest **fraction of an inch**.