If you're doing a whole number as one foot, then the fraction would be 2 and 8 over 12, which would simplify to 2 and 2 over 3.
The answer depends on as a fraction of WHAT!
To convert a fraction into a decimal, simply divide its numerator by its denominator. For example to convert 5/8 to a decimal, divide 5 by 8 to get 0.625.
2ft 6in
5/8
8/1000
8/19
7/8
0.125 into a fraction = 125/1000 or 1/8
1/8
it would be 8/5
81/8
2 and 2/3 = 8/3 as an improper fraction