It might depend somewhat on what you need to 'do' to the 400 sq ft.If the area is flat, such as a floor or a wall, it will take 225 of them.
16 sq. inches
16 km2 = 6.17763454 mi2
169/16 = 10.5625 of them.
16 sq yd 1 sq yd = 9 sq ft
16 square feet is equivalent to 1.49 square meters.
1280 sq ft
288 sq ft
About 160 square feet
If you mean 16 feet x 16 feet, then its 252 sq ft. Easy to figure out (16 times 16) 256 sq inches, or 1.777 sq ft.
16 sq ft = 1.486 sq metres (to 3 dp)
96 sq ft.