Common Fish Tank Sizes and Characteristics Tank SizeOutside Dimensions in Inches (L x W x H)Weight Empty and Full (lbs) 20 Long30 1/4 x 12 1/2 x 12 3/425 29 Gallon30 1/4 x 12 1/2 x 18 3/440 37 Gallon30 1/4 x 12 1/2 x 223/445 26 Flatback36 1/4 x 12 1/2 x 16 5/842 Read more...