I've just bought a fish tank. It's 41x61x61 cm.
What is its volume in gallons?
This is really a question about units. You need to know that 1 cubic centemieter = 1 millilitre = 1/1000th of a litre; and that 1 Imperial gallon = 4.54609188 litres (1 US gallon = 3.7854118 liters) (try http://www.google.com/search?q=1+imp...=Google+Search ).
In other words:
41*61*61=152,561cm3 for your tank
Something you can picture:
a 10cm *10cm*10cm cube is a litre
dived tank volume by 1,000:
Divide this by 4.5... for Imperial Gallons, or 3.78...
for US gallons, or stick with Litres like the civilised world :-)