How to figure out how much water is in my tank

[Mombo]

Just wondering if this is something that can be easily figured out. Doesn't need to be exact but trying to figure out an approximate. My tank is 120g 4x2 tank. It has 100lbs of dry rock and 60lbs of dry sand.....Then to figure out my sump...

Is there a calculator for something like that?

 

[CastAway]

One gallon is 231 cubic inches.

If the volume of water in inches was 48 x 23 x 18, you'd have 19,872 cu in, or, 86 gallons.

Not knowing the porosity of your rock, I think you can only guess at displacement; perhaps 10-15%.

Using this method for the display and sump should be pretty accurate.

 

[Bob Lauson]

Google "live rock volume". You can assume around 10 to 12 lbs of live rock is one gallon of water.

 

[madweazl]

I used this calculator to base my dosing on and was able to narrow it down from there. For my setup, it was within two gallons based on the dosing.

 

[Mombo]

Thanks, that worked well to give me an estimate. I should be close to 125 total gallons ish.