666 imperial cups in US customary teaspoons
Result
The conversion result is: 666 imperial cups is equivalent to 38391.9672185392 US customary teaspoons.[1]
Conversion formula
How to convert 666 imperial cups to US customary teaspoons?
We know (by definition) that: 1 brcup ≈ 57.645596424233 usteaspoon.
We can set up a proportion to solve for the number of US customary teaspoons.
1 brcup / 666 brcup ≈ 57.645596424233 usteaspoon / x usteaspoon
Now, we cross multiply to solve for our unknown x:
x usteaspoon ≈ (666 brcup / 1 brcup) * 57.645596424233 usteaspoon → x usteaspoon ≈ 38391.967218539176 usteaspoon
Conclusion:
666 brcup ≈ 38391.967218539176 usteaspoon

Conversion in the opposite direction
The inverse of the conversion factor is that 1 US customary teaspoon is equal to 2.60471153850409e-05 times 666 imperial cups.
It can also be expressed as: 666 imperial cups is equal to 1 / 2.60471153850409e-05 US customary teaspoons.
Approximation
An approximate numerical result would be: six hundred and sixty-six imperial cups is about thirty-eight thousand, three hundred and ninety-one point nine seven US customary teaspoons, or alternatively, a US customary teaspoon is about zero times six hundred and sixty-six 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.