To convert gigabytes to bytes, you multiply the number by 2^30 or 1,073,741,824. Many people mistakenly believe that gigabyte is simply a billion bytes, but the distinction becomes greater with larger file sizes. Computer memory exists in base-2 numbers, or the powers of 2. One kilobyte, for example, is actually 1,024 bytes, not 1,000.
A byte represents eight bits. A bit is a single binary digit,either 0 or 1. Each digit to the left in a byte represents an increasing power of two, the same way the digits represent powers of 10 in the decimal system, and all information in a computer is ultimately expressed in binary form at the lowest levels of operation. This is why, when you buy computer RAM, it is always expressed in powers of 2, such as 64 MB, 128 MB or 256 MB. The prefix "kilo-" was taken because nothing matched the exact conversion factor. Colloquially, people still express a gigabyte as a billion bytes.
Bits and bytes are two different measurements. Bytes are abbreviated with a capital B, whereas bits are abbreviated with a lowercase b. This has caused confusion, especially when dealing with network speeds that are expressed in terms of bits.