663 imperial gallons in US gallons
Result
The conversion result is: 663 imperial gallons is equivalent to 796.229800609719 US gallons.[1]
Conversion formula
How to convert 663 imperial gallons to US gallons?
We know (by definition) that: 1 imperialgallon ≈ 1.20094992550486 usgallon.
We can set up a proportion to solve for the number of US gallons.
1 imperialgallon / 663 imperialgallon ≈ 1.20094992550486 usgallon / x usgallon
Now, we cross multiply to solve for our unknown x:
x usgallon ≈ (663 imperialgallon / 1 imperialgallon) * 1.20094992550486 usgallon → x usgallon ≈ 796.2298006097221 usgallon
Conclusion:
663 imperialgallon ≈ 796.2298006097221 usgallon

Conversion in the opposite direction
The inverse of the conversion factor is that 1 US gallon is equal to 0.0012559188305113 times 663 imperial gallons.
It can also be expressed as: 663 imperial gallons is equal to 1 / 0.0012559188305113 US gallons.
Approximation
An approximate numerical result would be: six hundred and sixty-three imperial gallons is about seven hundred and ninety-six point two three US gallons, or alternatively, a US gallon is about zero times six hundred and sixty-three imperial 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.