Question 153974
Let's assume the room is a rectangle with sides L and W. The room is also H high. 
To calculate the surface area,SA, of the walls you would find the perimeter of the room and multiply by the H.
{{{P=2L+2W}}}
{{{SA=PH}}}
{{{SA=H(2L+2W)}}}
If you're painting the ceiling, you would add another {{{LW}}} worth of area (area of a rectangle).
If you're painting the floor too, that would add another {{{LW}}} worth of area.