For example, I have a litre of olive oil, but how much does it weight? Basically, it's simple - take the density of oil and multiply it by volume and you will recieve weight.
I came up with an idea to make a calculator on this issue (see below).
Then you have to set the volume as you like - litres, cubic metres, even length, width and height. Then it will calculate the weight.
Density in the reference book is set in grams per cubic centimeter. If any matter is absent in reference book somehow - registered users can always add it.