To purchase a 4ft fish tank one can visit many stores or purchase them online. One can get them from The Home Depot, eBay, Walmart and All Pond Solutions.
478.8 Gallon
In order to answer your question there is another dimension needed. width x length x depth = volume.
a tank top or skirt
That is 2.31 million cubic inches. The dimensions could change to whatever shape you needed, but an example would be somewhere around 20 feet wide x 8 feet high and 8 feet deep.
You cannot define a volume with only two linear dimensions.
2513.45 gallons.
A tank this size can hold a maximum of 3,590.65 US gallons of water.
Depending of the type of tank. Tanks i this time period varied in height from 4ft to 10ft+.
38.4 inches
Length x Width x Height / 231 is the equation to get gallons.
3456 square inches.
It can be 3.5 ft deep, but you may prefer to give them more "land" space.