gallons/liters equation for accurate calculation

[fugu]

would anyone know what the easiest equation for calculating liters and gallons of an aquarium would be . i have many different ones but i keep getting differentiating figures.
i have been using:
LxWxD IN INCHES DIVIDED BY 231
salt mixes never come out to the specs. on the packet due to miscalculation of capacity.
any ideas??

 

[broomer5]

Cubic inches of tank = L x W x D
then either
Multiply the cubic inches by .004329 to get U.S. gallons
or
Multiply the cubic inches by .01639 to get liters.
hope that is right
Brian

 

[fugu]

nice one mate! that seems to work out so far...cheers.alleviates some of the confusion.