How to resize text on android according to screen -

i working on android application in want set text size according screen. using following method, not re-sizing text size according screen.

myrequesttext.settextsize(convertfromdp(21));//myrequesttext textview public float convertfromdp(int input) {         final float scale = getresources().getdisplaymetrics().density;         return ((input - 0.5f) / scale);     }