Not really, most commonly sold plecs get to 12''+, the smallest about 6'' (I'm talking commonly sold, not things like clown pleco). Why does s/he want a plec anyway?
Get the tank measurements and someone can work it out. What kind of plec is it? If its a common or sailfin it will grow between 12 and 24 inches so it could get as long as a 2 foot tank. Have a look on planet catfish and see if you can id it. Heres a good site with loads of corys http/www.jjphoto.dk/fish_archive/mall3.htm
Corys like to live in groups of 3 or more.