Which the largest kilobyte gigabyte megabyte or terabyte?

From largest to smallest: Terabyte, gigabyte, megabyte, kilobyte.

Looking at the prefix of the Word will give you the answer. "Kilo" means 1000. "Mega" means one million. "Giga" means one billion. This prefix system is commonly used in the metric system as well, so feel free to read more about it.