Fiji Rock, water displacement

[Monkeynaut]

Does anyone have a good rule of thumb for the amount of water 1 pound of Fiji rock displaces? I understand some rocks will be more, others less. But I figure there must be a good average for this type of rock.

I have 90 pounds in my tank currently.

 

[Reefing Madness]

 

[Reefing Madness]

http://www.garf.org/calculators/tankvolumecalculator.asp

 

[Monkeynaut]

Great! His calculator states 7.48 gallons for 85 pounds. I didn't get the calculator to work on my phone but I can do that math.
Thanks again

 

[Reefing Madness]

There are other calculators out there for water displacement, this will give you a rough idea what your looking at.