Question 840829
Mass in English units is given in slugs, in metric it's kilograms.
Pounds are units of force or weight (mass x acceleration).
The fake unit is lb-m (for pounds mass).
One gallon of water contains 3785 ml, so 1 gallon has a mass of 
{{{3785*1.0=3785}}} in units of g. 
There are 454 grams in 1 lb-m. 
So then
{{{3785/454=8.34}}} lb-m
So 1 gallon of water has a mass of approximately 8.34 lb-m.