To determine the number of inches per foot from the equation \( 4y = 48x \), we start by rewriting the equation in a more interpretable form, focusing on how \( y \) (the number of inches) relates to \( x \) (the number of feet).
In the equation:
\[ 4y = 48x \]
we can simplify it by dividing both sides by 4:
\[ y = 12x \]
This equation shows that for every 1 foot (represented by \( x = 1 \)), there are 12 inches (represented by \( y \)). Thus, since there are 12 inches in 1 foot, we conclude that the number of inches per foot is:
\[ \boxed{12} \]