The Great Storage Confusion
Have you ever bought a 1 Terabyte (TB) hard drive, plugged it into Windows, and seen it reported as exactly 931 Gigabytes (GB)? You were not scammed—you just encountered the difference between decimal and binary units.
Decimal Units (SI)
Storage manufacturers and macOS use the standard SI prefixes (powers of 10):
- Kilobyte (KB): 1,000 bytes
- Megabyte (MB): 1,000,000 bytes
- Gigabyte (GB): 1,000,000,000 bytes
Binary Units (IEC)
Computer memory architecture (RAM, Windows OS) uses binary prefixes (powers of 2):
- Kibibyte (KiB): 1,024 bytes (2^10)
- Mebibyte (MiB): 1,048,576 bytes (2^20)
- Gibibyte (GiB): 1,073,741,824 bytes (2^30)
Because Windows uses binary logic (1,024) but labels them as "GB", a 1,000,000,000,000 byte drive (1 TB) displays as 931 GiB (labeled "GB").
Use our tool to easily convert between base-10 storage marketing sizes and base-2 operating system sizes to know exactly how much space you really have.