To express the number 78 as a percent, you take the number and divide it by 100. In decimal form, this means:
\[ 78 = 78 \times 1 = 78% \]
If you need it in decimal form (as a fraction of 100), it is:
\[ 0.78 \]
Thus, 78 expressed as a percent in decimal form is:
\[ \boxed{0.78} \]