I mentioned that site in a previous email. It may not have a symbol for "ft", but you can just type in the ft. IIRC, the problem is that it will automatically convert to meters which will confuse matters.

Cut n paste the following into it: 2m^2 * 2m^2

The "m" means meters. It returns the correct result.

The cut n paste the following: (2m)^2 * (2m)^2

Should be a different answer. The CONVENTION is that the square only applies to the next nearest thing to the left - no matter what that thing (variable, constant, unit, function) UNLESS the order is altered by parentheses.