How to calculate tank volume?

[SanFranTodd]

What is the formula to calculate the volume of water in a tank?

Thanks

[willra]

Length x Width X Height (in inches) / 231 = Gallons

There are 231 cubic inches for 1 gallon of water. It usually ends up less because of the glass and overflows space.

[ricka]

I'm not sure this formula works.

I have a 125G tank that is 60 x 18 x 24.

By this formula, I only have a 112 gallon tank.

[David M]

The 231 is correct. Yup, that's right, they LIED to you :D If you look at the label on a new tank it does not say 40 (or 90 or whatever) gallons, it typically says something like Model 40R. In fact a standard 40 gal breeder tank holds 35 gals of water. A standard 60 holds 48 gallons, and so on. Some sizes are closer to reality than others, such as a110 which actually holds 112 gallons of water. A fifty tall holds pretty much a true 50. The actual capacity of the tank is usually written on the label somewhere in liters. As Americans, we are expected to be too stupid to do the math. Remember to use the inside dimensions, not the exterior, and measure the height to the actual water level, not the top of the frame. You may be surprised how small your tank really is. Then deduct for lr and substate. A typical 55 reef tank has maybe 40 gallons of water in it if your'e lucky.

[willra]

ricka - Yeah, thats interesting. I guesss an AGA 120 holds more than an AGA 125.

[wetworx101]

Uh, David, you may be exagerating your margins of error...it often isnt that much, maybe a gallon or two. A 40long is 48"x13"x16"...actually 43.2gallons...a 40 breeder is 26"x18"x16"...44gallons.
Now, these dimensions are taken from the outside, and the tanks interior is a little bit smaller due to glass thickness, but not by much. As you can see, the calculations prolly take this into account. Sure, sometimes we end up with a little less, but rarely.
You guys need to do your math again, and get the specs right in the first place!
A standard 125g is not 60"long! It's 6 feet...72"! 72x18x22 = 123g. A 120 48x24x24 = 119g. Not too far off. Heck, I bet the depth pressurizes the water at 18 and 24" and an extra gallon or two IS in there...
A 50breeder, 36x18x18 = 50g
A 65breeder, 36x18x25 = 70g!
A 55L, 48x13x21 = 56.7g
Nobody lied, AGA isnt scamming, and a 125 is still bigger than a 120. You guys need to quit making up tank dimensions and learn math....der....:p

[willra]

Thank you wet works for clearing that up. I got confused, I was thinking 6 feet was 60 inches .... doh. I don't think AGA is scamming.

[ricka]

wetworx,

Check out the 125H on the tenecor site:

http://www.tenecor.com/rectangular.php

125H 60 x 18 x 24 $630 $1037 $1464

Clearly, they sell a 60 inch 125 gallon tank. You point is well taken about the outside vs the inside of the glass, but I have a hard time believing that 1/2 of an inch of acrylic is worth 12 to 13 gallons.

[David M]

Actually since I have large multi-tank systems it is very important to me to know the exact water volume of each system. Just In case my memory had failed me I just double checked a "40". Interior dimensions are 35.5 X 15.5 X 15 or 8253.75 Cu In. Divide by 231= 35.7 gallons. I will stand on my memory for the other sizes. It's straight forward math, there are no "margins of error" to exagerate. :p

And no willra, AGA is not misleading you. I seriously doubt you can find anything on that tank that says it holds 120 gallons. Then again as I said above some are more accurate than others and maybe AGA is pretty close. Measure it yourself and see.

[wetworx101]

Ok, see the tenecor now....that is a rip. Only 112gallons!

Yes, yes , yes, to be exact, one should measure from the inside of the glass (I said there is some gallonage lost due to this before)...so my 60/24" cube ...and I'll admit a 60 cube isnt really a 60 up front...with 3/8" glass is really 23.25x23.25x23 (water is one inch below surface), or 53gallons...loosing me 6 gallons in a 60 gallon (really a 24" cube is only 59g)..thats 10%! (and you were saying ricka...??? glass thickness costs some serious size when you take in to account all three dimensions are being reduced).
So I suppose we should file suit. Just goes to show, do your math cuz you never know what someone might be trying to scam.

Then again, we are reefers. We have no real basis to get picky, after all, lets say we have a 40 gallon breeder, I gotta defend AGA here first... I dont know where dave got his figures, but I measured one of mine. Interior is measured (just did it) as 35.5"long, 17.5"wide (what tank are you getting 15.5 from Dave?), and water depth is a nice 15.5" high. The height on the outside is actually well over 16" because of the bottom glass and the thick trim, so my water level, actually could be topped off a little more, is 15.5"...not bad for a tank advertised at 16", or specified as 16 - 7/8" on the back of their catalog. Do the math...comes out to 41gallons!!!!!! Hah! Still bigger than advertised!!!

Sorry Dave, your 40 aint a 40. Dont know of any common tanks made at 16" front to back...all 12", 13", 18", or 24".

But heres why we shouldnt be so picky. In that 40 we will often put 40lbs of sand/gravel, 60some pounds of rock, and then the critters. Sometimes we have an overflow box in the back corner taking up 3gallons...By the end we are lucky sometimes if we have 20 gallons left in there of actual sea water. Whatcha gonna do?