MB vs MiB: decimal and binary storage explained
Understand why 1 MB is not the same as 1 MiB and why storage sizes can appear different.
Last reviewed: 2026-07-29MB is decimal: 1 MB equals 1,000,000 bytes. MiB is binary: 1 MiB equals 1,048,576 bytes. The labels look similar but use different multipliers.
Decimal prefixes
Storage manufacturers commonly use SI decimal prefixes: KB is 1,000 bytes, MB is 1,000 KB and GB is 1,000 MB.
Decimal units make product capacities easy to scale by powers of ten and match the normal SI meaning of kilo, mega and giga.
Binary prefixes
Computer memory and some operating-system displays use powers of 1024. The unambiguous names are KiB, MiB and GiB.
1 GiB equals 1,024 MiB, while 1 GB equals 1,000 MB. Converting between them changes the numeric value but not the underlying number of bytes.
Why capacity looks smaller
A drive advertised in decimal GB can show a smaller number when software divides the same bytes by binary powers. Formatting and system files may reduce available space further.
Always compare units as well as numbers. A converter should first reduce the value to bytes, then divide by the target unit.