We all know that a US gallon is 1/5 smaller than an Imperial gallon don`t we? It is 128 oz in a US gal. compared to 160 oz in an Imp. gal. Clearly a ratio of 4/5 or 1/5 smaller, right? WRONG!!! A US gal. is only 1/6 smaller than an Imperial gal. WWWhhhaaaaattttt??? you are saying to your self. Don`t leave yet-it is true. I will explain. You can grab your service manual and check my conversion factors if you want.
1 US gallon / 1 Imp. gallon
3.785 liters / 4.546 liters = 0.8326 = 5/6 (approx.)--1/6 smaller not 1/5
(3785 mililiters) (4546 ml)
So don`t leave yet, I can see your eyes glazing over.
we are almost there.
Let`s do one more comparison, ok 2 more. 1 US gal. = 3785 ml / 128 oz. = 29.57 ml/ US oz.
1 Imperial gal. = 4546 ml /160 oz. = 28.41 ml / Imp. oz.
And therin we have the solution to our little mystery, the US ounce is approximately 1.16 ml larger than the Imp. oz. This makes the difference of just over 5 additional oz. in a US gal. which is enough to change the ratio to 5/6 instead of 4/5.
Well this might be useful to somebody someday. I just found it interesting.