Space in tanks

Question
Hi... how can you work out how many fish your tank can fit.
Or how many inches/cm of fish you can hold. I heard that if you multiply the length and width of a tank, then divide it by 30, that will equal the amount of fish you can put in, like if the answer to the sum was 20cm, that means you would be able to put 5 guppies in (which are 4cm each)... is this formula OK?

Answer
Hello Sameem:  Sadly there is not a magic formula to answer your question because many different factors are involved in determining the number of fish per tank.  Factors such as aggression, tank layers (top, middle, bottom), maintenance schedules, etc.  I have always used the one inch of fish per gallon rule to estimate the maximum number of fish but not the types of fish.  For example a 55 gallon tank will hold ONE OSCAR.. maybe two depending... or the same 55 gallon tank can hold 40-55 guppies.  dave