What rule do you use to stock tanks?

Experience/research.

well i have always hated that stupid 1 inch per gallon rule, it only works out for small tetra's. I normally just look at the fishes max size and just sort of wing it. I meen a 10 inch oscar in a 10 gallon tank, or even a 15, 20, or 29 gallon tank for that matter just doesnt work out. I really dont believe there is an exact rule or formula out there that can be used for all fish, there always seems to be an acception. Anyways thats my 2 cents

Surface area rule is better than gallon rule, but still doesn't really work. A 20 tall can basically hold the same amount of fish as a 15 because they have the same surface area. (surface area exposed to air) I go by the rule that every tank is over stocked, so if it looks like it is stocked properly, then its over stocked. If it looks understocked, then its good.

I've seen the 1 inch per 32 inch guideline bandied about for marine tanks: 1 per 10 to 12 was given for freshwater. There is mostly open hostility to the 1 inch per gallon rule around these parts.

Generalizations, in general, tend to oversimplify. I like the area guide better than the inch per gallon but I think it still has shortcomings. I think the idea that a 2 inch fish=8 1 inch fish is just flat out silly.

If you were to start with the area guide and then modify for body type, diet, activity level, and general size you might start getting somewhere.

Does a 2 inch rasbora have the same bioload as a 2 inch danio? Does a carnivore have the same bioload as a vegetarian with the same mass? How massive is the fish (best guess) and isn't that much more important than its length? What is a reasonable expectation of adult size and how does that skew the calculations, especially for small fish?

Its easy to say experience once you have it. If you don't, area is a nice place to start but volume is also important—its both and not one or the other. And then different fish are different. You're more likely to be successful if you take those differences into account then if you don't.

Fish color, behavior, and health are all going to be better/more natural/more interesting in a moderately/lightly stocked tank. Overstocking is a good way to not enjoy a tank.

Other- test your water as you go. Your readings will tell you all you need to know.

I go with surface area, but with a different ratio for slim fish versus full-bodied fish (see my sig). It's only a rule of thumb, and of course temperament, food sources and other particulars need to be considered, as the others have posted. But I find it helps me at least ball park what I can and cannot have in a tank. You gotta start somewhere.

I tend to look at the adult size of a fish, and figure out if it'll have enough room to turn around and get some exercise. if a fish can only hang there and not swim around what fun is it?

right now it isn't a problem for me since i have all small fish in my tank. with small fish basically if my tank looks crowded it's probably too full, and if there is plenty of open swimming space it's probably just about right or a little understocked, which isn't a bad thing.

I have to agree that alot of know if a tank is over stocked comes from experience and common sense. Also, I have to agree with joephys's point about if it looks good its overstocked and if it looks understocked then you are good. I think that is a pretty good way to explain it to people who don't have alot of experience. When I first started and I was learning about stocking I remember thinking how empty my tank looked but now that I am used to it, the tank looks normal. I think alot of new people who are just starting out and dont know alot about fish are basing much of thier stocking plans on what they see in the fish store, ie. 100 neon tetras or 30 blue rams in a 10gallon. :thud: That is, at least until they come here!!!
I also think the use of test kits is smart to make sure the tank isn't above its max bioload. You can't go wrong with a test kit so long as you know it is accurate. Although, a test kit won't tell you that you shouldn't put a Jack Dempsy in with neon tetras unless you wanted to buy some expensive feeder fish but I guess that's where research and common sense come in! But I guess we are going with numbers not species here!