13 imperial cups in US customary cups
Conversion
13 imperial cups is equivalent to 15.6123490315631 US customary cups.[1]
Conversion formula
How to convert 13 imperial cups to US customary cups?
We know (by definition) that:
We can set up a proportion to solve for the number of US customary 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 US customary cup is equal to 0.0640518603560761 times 13 imperial cups.
It can also be expressed as: 13 imperial cups is equal to US customary cups.
Approximation
An approximate numerical result would be: thirteen imperial cups is about fifteen point six zero US customary cups, or alternatively, a US customary cup is about zero point zero six times thirteen imperial cups.
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.