The question, as stated, cannot be answered sensibly. A gallon is a measure of volume, with dimensions [L3]. A milligram is a measure of mass, with dimensions [M]. The two measure different things and basic dimensional analysis teaches that you cannot convert between measures with different dimensions such as these without additional information.
As a simple mental exercise consider a gallon of air and a gallon of water. They will have very different masses.
Chat with our AI personalities
1 mg equals how many grams?
1000 mcg equals 1 mg.
1 US gallon = 3785.41178 cc
2 qts 1 gallon = 4 quarts 1 quart = 0.25 gallon
1 g = 1,000 mg 5 g = 5,000 mg