The answer is 16,000,000,000 bytes.
That is if the memory stick capacity is rated in decimal giga bytes which is more or less the norm for disk drives.
However Microsoft use binary giga bytes in Windows which cause no end of confusion because people who don't know the difference assume they are losing a shed load of capacity when in fact they are not.
Decimal measures are based on multiples of 1000, binary measures are based on 1024 which is the nearest power of 2 to 1000.
So a decimal giga byte is 1000 x 1000 x 1000 = 1,000,000,000
A binary gigabyte is 1024 x 1024 x 1024 = 1,073,741,824
A memory stick spec'ed as 16GB by the maker using decimal measures will appear in Windows as 14.9012GB (ish)which uses binary. But 14.9012 x 1,073,741,824 = 16,000,000,00 (or very close).