Data & Storage · 5 min read

How to Convert Gigabytes to Terabytes (GB to TB): Decimal vs Binary Storage

Have you ever bought a brand-new 1 Terabyte (1 TB) external hard drive or SSD, plugged it into your Windows PC, and felt cheated when Windows reported only 931 GB of usable space? This is not missing storage—it is the result of the historic clash between Decimal and Binary measurement systems.

Written by the Toolseza team · Updated 2026-10-31

Decimal (SI) vs Binary (IEC) Storage Systems

Hardware manufacturers (Samsung, Western Digital, Seagate, Apple) use the International System of Units (SI) decimal standard where prefixes represent powers of 10:

• 1 Kilobyte (KB) = 1,000 Bytes

• 1 Megabyte (MB) = 1,000,000 Bytes

• 1 Gigabyte (GB) = 1,000,000,000 Bytes (10^9 Bytes)

• 1 Terabyte (TB) = 1,000,000,000,000 Bytes (1,000 GB or 10^12 Bytes)

Operating systems like Microsoft Windows, however, organize memory in binary architecture (powers of 2):

• 1 Tebibyte (TiB) = 1,024 Gibibytes (GiB) = 1,099,511,627,776 Bytes (2^40 Bytes)

Why Your 1 TB Drive Shows 931 GB in Windows

When a hard drive manufacturer builds a 1,000,000,000,000-byte disk, they label it 1.0 TB. When Windows reads the exact same disk, it divides the bytes by 1,024 three times to convert to gigabytes: 1,000,000,000,000 ÷ 1,024 ÷ 1,024 ÷ 1,024 = 931.32 GiB.

Windows labels this result as "GB" instead of "GiB", which causes the widespread misconception that 69 GB of space vanished.