Why does my 1 TB hard drive show only 931 GB in Windows?

Your drive contains exactly 1,000,000,000,000 bytes as advertised. Windows reports storage in GiB (gibibytes) but displays the label "GB": dividing 1,000,000,000,000 bytes by 1,073,741,824 (bytes per GiB) gives approximately 931. No storage is missing.

What is the difference between MB and MiB?

1 MB (megabyte, SI) = 1,000,000 bytes. 1 MiB (mebibyte, IEC) = 1,048,576 bytes. The difference is about 4.9%. For small files this is negligible, but at the terabyte scale the gap becomes significant.

How many bytes are in a gigabyte?

In the SI (decimal) definition used by drive manufacturers: exactly 1,000,000,000 bytes (10⁹). In the IEC (binary) definition used by operating systems: exactly 1,073,741,824 bytes (2³⁰).

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How to Convert Data Storage Units — KB, MB, GB, TB Free (2026)

By Rui Barreira · Last updated: 18 June 2026

Converting between kilobytes, megabytes, gigabytes, and terabytes seems straightforward until you discover there are two competing definitions for each unit. The data storage converter handles both the decimal (SI) and binary (IEC) systems simultaneously, so you always get the right answer for your context.

How to Use the Tool

Enter a numeric amount in the input field.
Select the unit you are converting from (e.g. GB, MiB, TB).
The tool instantly displays the equivalent value in every other unit, showing both decimal (KB, MB, GB, TB) and binary (KiB, MiB, GiB, TiB) results side by side.

SI (Decimal) vs IEC (Binary): Why They Differ

The confusion arises because "gigabyte" has two valid meanings depending on the context:

SI (decimal, base-10): 1 GB = 1,000,000,000 bytes exactly. Used by hard drive and SSD manufacturers, network speeds, and most consumer electronics marketing.
IEC (binary, base-2): 1 GiB = 1,073,741,824 bytes (2³&sup0;). Used by operating systems (Windows, macOS, Linux) when reporting available storage and RAM.

This is why a hard drive advertised as "1 TB" (1,000,000,000,000 bytes by the manufacturer's definition) shows up as approximately 931 GB in Windows or macOS: the OS is reporting in GiB but labelling it GB. No storage is missing—the same number of bytes is there; only the unit definition differs.

Use Cases

Comparing storage devices: convert a drive's advertised TB capacity to the GiB figure your OS will report.
Networking: convert between megabits per second (Mbps) and megabytes to understand real-world download speeds.
Programming and cloud infrastructure: check memory limits, file size thresholds, and API payload caps expressed in different units.
Understanding file sizes: verify whether a file fits within an email attachment limit or a cloud storage quota.
Buying decisions: compare storage specs across devices that use different labelling conventions.

Frequently Asked Questions

Why does my 1 TB hard drive show only 931 GB in Windows?: Your drive contains exactly 1,000,000,000,000 bytes as advertised. Windows reports storage in GiB (gibibytes) but displays the label "GB": dividing 1,000,000,000,000 bytes by 1,073,741,824 (bytes per GiB) gives approximately 931. No storage is missing; it is purely a unit labelling difference between the manufacturer (decimal GB) and the operating system (binary GiB).
What is the difference between MB and MiB?: 1 MB (megabyte, SI) = 1,000,000 bytes. 1 MiB (mebibyte, IEC) = 1,048,576 bytes. The difference is about 4.9%. For small files this is negligible, but at the terabyte scale the gap becomes significant—which is why the discrepancy is noticeable when buying large drives.
How many bytes are in a gigabyte?: In the SI (decimal) definition used by drive manufacturers: exactly 1,000,000,000 bytes (10&sup9;). In the IEC (binary) definition used by operating systems: exactly 1,073,741,824 bytes (2³&sup0;). When precision matters—such as in programming or filesystem work—use "GiB" to mean the binary version and "GB" to mean the decimal version.

Frequently Asked Questions

Why does my 1 TB hard drive show only 931 GB in Windows?: Your drive contains exactly 1,000,000,000,000 bytes as advertised. Windows reports storage in GiB (gibibytes) but displays the label "GB": dividing 1,000,000,000,000 bytes by 1,073,741,824 (bytes per GiB) gives approximately 931. No storage is missing.
What is the difference between MB and MiB?: 1 MB (megabyte, SI) = 1,000,000 bytes. 1 MiB (mebibyte, IEC) = 1,048,576 bytes. The difference is about 4.9%. For small files this is negligible, but at the terabyte scale the gap becomes significant.
How many bytes are in a gigabyte?: In the SI (decimal) definition used by drive manufacturers: exactly 1,000,000,000 bytes (10⁹). In the IEC (binary) definition used by operating systems: exactly 1,073,741,824 bytes (2³⁰).