639 US quarts in US gallons
Result
The conversion result is: 639 US quarts is equivalent to 159.75 US gallons.[1]
Conversion formula
How to convert 639 US quarts to US gallons?
We know (by definition) that: 1 usquart ≈ 0.25 usgallon.
We can set up a proportion to solve for the number of US gallons.
1 usquart / 639 usquart ≈ 0.25 usgallon / x usgallon
Now, we cross multiply to solve for our unknown x:
x usgallon ≈ (639 usquart / 1 usquart) * 0.25 usgallon → x usgallon ≈ 159.75 usgallon
Conclusion:
639 usquart ≈ 159.75 usgallon

Conversion in the opposite direction
The inverse of the conversion factor is that 1 US gallon is equal to 0.00625978090766823 times 639 US quarts.
It can also be expressed as: 639 US quarts is equal to 1 / 0.00625978090766823 US gallons.
Approximation
An approximate numerical result would be: six hundred and thirty-nine US quarts is about zero US gallons, or alternatively, a US gallon is about zero point zero one times six hundred and thirty-nine US quarts.
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.