To find the length of the diagonal of a square, you can use the formula:
\[ d = s \sqrt{2} \]
where \( d \) is the length of the diagonal and \( s \) is the length of a side of the square.
Given that the side length \( s \) is 14 inches:
\[ d = 14 \sqrt{2} \]
Now, calculating \( \sqrt{2} \) gives approximately 1.414. Therefore:
\[ d \approx 14 \times 1.414 \approx 19.596 \]
Thus, the approximate length of the diagonal of a square with a side length of 14 inches is about 19.6 inches.