This is a good resource to find a starting density for products.
If you have a flow only system, you may just use 1 gram/milliliter (specific gravity) for everything. This is the density of water.
If you cannot find the density of a product and you have an inductor, you can use the following steps to find the density. This method is also suggested to fine tune the density of the product you are using.
1) Set an empty jug on the scale
2) Go into manual mode and turn on the scale reading
3) Remove the empty jug (weight will go negative)
4) Set full jug on the scale
5) Density = Weight/Size of Container (EX: 9.4 Pounds/Gallon = 23.5 Pounds/2.5 Gallons)