10 gallon rule for leopard geckos
There seems to be a 10 gallon minimum rule per leopard gecko amongst experienced hobbyists. What that means in accordance to actual floor space, I do not know. Personally I would recommend starting with a 20 gallon, with a floor space of 24x12 inches, for one gecko and add about 10 gallons worth of floor space for each gecko you plan to add. So if, say, you wanted three leopard geckos, you would probably want a tank or some other type of terrarium build to approximate 40 gallons and 36x24 inches of floor space. If you can't find a tank that acommodates these dimensions - and most standard-built tanks don't - the 36x12.5 inch tanks would probably do. I used to have one of those for my second leopard gecko Jubjub before I moved him to a 20+ gallon tank and gave the 35 gallon to my fire skink.