Check out example codes for "css calc font size". It will help you in understanding the concepts better.

Code Example 1

html { font-size: calc(1em + 1vw); }

Code Example 2

/*Here a possible solution:*/

http://codepen.io/CrocoDillon/pen/fBJxu

p {
  margin: 0;
  font-size: calc(4vw + 4vh + 2vmin);
  /* See:
   * http://codepen.io/CrocoDillon/pen/jgmwt
   * For some math behind this
   */
}
/*Font-size is calculated with available size using a function that is not 
perfect, but may be adjusted to work well in some cases.*/

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