What Do You Think Is The Minimum Size For An Oscar?

I got into a friendly argument with a friend with how big is the minimum size for an oscar. He says 55, but I say 40 gallon breeder because of the extra room to turn around in? He is thinking about getting an oscar. So who is right, me or Billy(my friend)?

 I don't mean to criticize the website calculator, but that is WAY off.  You dont need 142 gallons for an oscar. So that means we were both wrong? I'm gonna tell Billy NOT to get an oscar.

The problem with just giving the volume is that it doesn't say how long and how tall the tank is. That's why I had to guess at the height of a 6 foot tank to work out the volume. But just because tanks that size in the UK are 18 or 24 inches tall doesn't mean that American 6 foot tanks are the same height.
Seriously Fish just gives the footprint of a tank needed for an oscar, it doesn't give a volume.

For instance, the Juwel Rio 400 tank is 151cm long - 59.5 inches; 51cm front to back - 20 inches; and 66cm tall - 26 inches. According to SF, this tank is not big enough for an oscar as it is only 20 inches front to back and an oscar needs 24 inches. This tank's volume is 450 litres, or 119 US galls. The thing that makes the volume so large for a 6 foot tank is the height, 26 inches.