Here are the most common room sizes and their square feet totals (length x width = sqft):
10 x 12 = 120 Sqft
12 x 12 = 144 Sqft
12 x 14 = 168 Sqft
14 x 16 = 224 Sqft
16 x 12 = 192 Sqft
18 x 15 = 270 Sqft
20 x 18 = 280 Sqft