Volume (also called capacity) is a quantification of how much space an object occupies.
The SI (International System of Units ) unit of volume is cubic metre ( meter in american english) , equal to 1000 liters, 1.307 95 cubic yard, or 35.3147 cubic feet. A cubic meter holds about 219.99 British Imperial gallons or 264.17 U.S. liquid gallons.
Some people need to calculate the water displacement of an object a rock for example, but it is imposible to calculate this with a general volume conversion calculator because the density of different rocks and because objects have regular or uniform shapes and irregular shapes.
In general people want to know what the volume of water is in their fish tank ? For example you have a 100 gallon tank that has about 120 lbs of rock and a 5 inch sand bed over a plenum. In general you can approximate live rock volume at 7.48 gallons per 85 lbs of rock.Also is important the type of rock, for example: in case you have a maricultured rock, which is not very porous, the water will reside around it, but if you have a porous rock, much of the water will reside within the rock.
One solution is you take a container and fill it with certain amount of water and mark the height of the water. Then add some rock, wich will cause the water line to rise. Mark the new water level.Remove the rock.Measure how much water is needed to meet the raised water line. This tells you the volume of the rock. Based on this you can get an estimated formula.