How many bytes in a GB?

A gigabyte in binary is exactly 2 to the 30th power bytes, which works out to 1,073,741,824. Operating systems, RAM chips, and most desktop software use this definition because memory addresses are binary. When you check a file size or free disk space in your OS, that number is in binary bytes.

In decimal SI units, a gigabyte is exactly one billion bytes (1,000,000,000). Drive manufacturers, ISPs, and anything referencing the International System of Units uses this definition. The difference is small at the MB level (about 5%) but grows to 7% at GB, 10% at TB, and keeps widening.

Quick reference: Gigabytes to Bytes

Worked examples

1. Example 1: You are writing a script that processes log files and want to know how many bytes you can fit in 2 GB of memory.

   Calculation: 2 GB × 1,073,741,824 = 2,147,483,648 bytes.

   You can buffer about 2.15 billion bytes. Use binary because RAM is binary.

2. Example 2: A database row averages 512 bytes. How many rows fit in 1 GB?

   Calculation: 1,073,741,824 ÷ 512 = 2,097,152 rows.

   About 2.1 million rows fit in 1 GB of binary storage at that row size.

3. Example 3: You transfer 3 GB over a 1 Gbps network connection at full speed.

   Calculation: 3 GB × 1,000,000,000 bytes (decimal, network) = 3,000,000,000 bytes. ÷ 125,000,000 bytes/sec (1 Gbps) = 24 seconds.

   Network transfer time calculations use decimal, not binary.

← Back to all answers