The "one inch per gallon" rule

[AW7020]

Thanks for the clear explanation for the cubic inch rule. Sure clear up a number of questions for me. Cheers.

This is something that comes up fairly often and is rather misunderstood therefore I will attempt to clarify the original meaning of the general guideline of "one inch of fish per gallon of water".

This is a suggested guideline for a well maintained and filtered tank.
It does not apply to all fish as some have differing requirements.

Here is the part that is being misunderstood.

The "rule" does NOT refer to the length of the fish!

The "rule" applies to the cubic inches of fish in the tank.

 

[pcfriedrich]

seems like common sense, if you think about it. you gonna fit a 72" shark in a 75 gallon aquarium? hell, the aquarium is only 48" long! always try to give your fish as much space as possible. you could easily keep 50 guppies in a 55 gallon, though.

 

[scubasteve06]

I think if there is a rule at all it should be 1 inch for every 5-10 gallons...and this still isn't accurate because of each fish's individual needs.

 

[Passionate 4 pikes]

I dont go bye the rule at all i have a basic idea of how many fish can go into the tank cuz if you have really good filtration you can go a little over...

 

[Blue Butcher]

I have three large fish 26",22",18" and 6" = 72", all in a 200 gallon with plenty of room to be happy. I can't say that rule works for me.

 

[bluekrissyspikes]

i hate the inch per gallon rule! i gave my freind my old 10g(way too small for me). I told her she could probably put a betta in there, a couple cories, guppies or some tetras. so what does she do? takes it home, sets it up, takes all the gravel and filter out and rinses it in bleach water(way to uncycle it). then she goes and gets 2 5" cat sharks to put in there. now she keeps arguing that they are ok in there. i look at them and they seem to always be gasping for air. arrgh!! one in per gallon my bum. would you try to cram a 20" fish in a 20 gallon? i sure wouldn't!

 

[MalawiFan]

My boyfriend has an excellent method. I keep adding fish until he says "holy **** that's a lot of fish" then I'm done. LOL
I just keep an eye on the parameters as well as how often I have to do water changes and how dirty the water is... I recently took 5 fish back to my lfs because of this, and now my tank is doing very well and is clean. My tank is all barbs, so they like a group and swim together. With fish that need space I'd use less fish/gal.

this is the modified method i have been using for years...
when my wife tells me thats enough fish for that tank I just go buy another tank.

lets see...
55 gal
20 gal
2 x 30 gal breeders
3 x 10 gal (baby catchers)
40 gal breeder
and now a 90 gal
with plans for a brand new 210 soon (this summer if im really good)

 

[dcdgoodtimes]

the the more room the better too. hiding places and rock make a difference you could have a 20 gallon tank but if u have substrate, rocks, caves, hiding places a take up room also SO DON't FORGET THOSE OTHER VARIABLES

 

[dcdgoodtimes]

This is something that comes up fairly often and is rather misunderstood therefore I will attempt to clarify the original meaning of the general guideline of "one inch of fish per gallon of water".

This is a suggested guideline for a well maintained and filtered tank.
It does not apply to all fish as some have differing requirements.

Here is the part that is being misunderstood.

The "rule" does NOT refer to the length of the fish!

The "rule" applies to the cubic inches of fish in the tank.

This means that a 5" gourami should be measured in this manner,
length overall (5"),
thickness, (1/2"),
height, (2 1/2"),
so for this fish you multiply the following, 5x 1/2x 2 1/2, this gives you a total of 6 1/4 gallons of water.

For small fish like glo-light tetras you will end up with something like this,
1 1/2"x 1/4"x1/2", this comes to 3/16 of a gallon (about 1/5), and that gives you 5 fish of this size per gallon (quite reasonable)

For larger fish you end up with something like this, my example here will be a silver arowana at 24" long, 24"x 4"x 1", which gives you 100 gallons of water.

As you can see this works fairly well.

You do also have to apply some common sense and allow for such things as potential growth, the fish types' tolerance for crowding, and of course the width and length of the tank (a 24" gar will not work in an 18" wide tank even if the tank holds 100 gallons).

So please people, accept that this is just a generalized guideline to figure potential stocking levels, not a hard and fast rule.
Also remember that just because you don't like it doesn't mean you should slam somebody for using it.
And lastly, please don't flame someone by saying a 10" oscar doesn't fit in a 10" tank.
Of course it doesn't,
but the rule never said it would.

THE WATER IN THE TANK MIGHT NOT BE AS MANY GALLONS AS U THINK
the the more room the better too. hiding places and rock make a difference you could have a 20 gallon tank but if u have substrate, rocks, caves, hiding places a take up room also SO DON't FORGET THOSE OTHER VARIABLES

 

[bassman24]

Glass/acrylic thickness can make a huge difference on actually gallons. I bought a 240 w/3/4 inch acrylic that actually came out to about a 215.