How many terabytes are in a zettabyte?

1 kilobyte = 1024^1 = 1,024 bytes
1 megabyte = 1024^2 = 1,048,576 bytes
1 gigabyte = 1024^3 = 1,073,741,824 bytes
1 terabyte = 1024^4 = 1,099,511,627,776 bytes
1 petabyte = 1024^5 = 1,125,899,906,842,624 bytes
1 exabyte = 1024^6 = 1,152,921,504,606,846,976 bytes
1 zettabyte = 1024^7 = 1,180,591,620,717,411,303,424 bytes

So there are 1024^7 / 1024^3 gigabytes in a zettabyte.
1024^7 / 1024^3 = 1024^4 = 1,099,511,627,776 gigabytes in a zettabyte..!

If you are using the purist SI units meaning of "giga-" and "zetta-" then this would be:
1000^7 / 1000^3 = 1000^4 = 1,000,000,000,000