(Length of area * width of area * cost of floor materials in square feet + (length + width) * cost of railing per foot + permit or inspection fees) / (length * width)= cost of building a deck per square foot.

Cost per Square Foot = Total cost of deck / area of the deck
If the deck is rectangular, then area of the deck would be length multiplied by width (all in feet).

First, figure out the dimensions of your project. Then determine the area of your deck project. If your project is not a square or rectangle you need to add those extra ares. Then get an estimate of the cost of the project. Finally you would divide the cost in dollars by the total square footage (Cost $/square foot area).

Add the total cost to build the deck,including material, labor, blueprints, permits, etc. Calculate the total surface area in square feet. Divide cost by area. COST/AREA=Cost per square foot.