391 US gallons in imperial cups
Conversion
391 US gallons is equivalent to 5209.20969903895 imperial cups.[1]
Conversion formula
How to convert 391 US gallons to imperial cups?
We know (by definition) that:
We can set up a proportion to solve for the number of imperial cups.
Now, we cross multiply to solve for our unknown :
Conclusion:

Conversion in the opposite direction
The inverse of the conversion factor is that 1 imperial cup is equal to 0.000191967699089651 times 391 US gallons.
It can also be expressed as: 391 US gallons is equal to imperial cups.
Approximation
An approximate numerical result would be: three hundred and ninety-one US gallons is about five thousand, two hundred and nine point two one imperial cups, or alternatively, a imperial cup is about zero times three hundred and ninety-one US gallons.
Footnotes
[1] The precision is 15 significant digits (fourteen digits to the right of the decimal point).
Results may contain small errors due to the use of floating point arithmetic.