Why does my 1 TB drive show as 931 GB?

The drive is 1 trillion bytes (decimal TB). Windows divides by 1024 three times to display GB, giving 931. It is actually 931 GiB but Windows labels it GB.

In decimal, 1 GB = 1000 MB. In binary, 1 GiB = 1024 MiB.

What is the difference between Mbps and MB/s?

Mbps is megabits per second (network speed). MB/s is megabytes per second (file transfer). Divide Mbps by 8 to get MB/s.

How many bytes in a kilobyte?

Decimal (SI): 1 KB = 1000 bytes. Binary (IEC): 1 KiB = 1024 bytes.

What comes after a petabyte?

Exabyte (EB), zettabyte (ZB), yottabyte (YB). Each is 1000 of the previous unit (decimal).

Data Storage Converter

Value

Enter the storage amount to convert

From Unit

To Unit

Formula

Bytes = value × fromFactor; Target = bytes / toFactor

Decimal units (KB, MB, GB, TB) use powers of 1000. Binary units (KiB, MiB, GiB, TiB) use powers of 1024. The converter first reduces the input to bytes, then divides by the target unit factor. Storage manufacturers use decimal; operating systems often display binary.

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TL;DR

Convert any data storage amount between bits, bytes, KB, MB, GB, TB, PB and the IEC binary versions.

Convert digital storage between bits, bytes, kilobytes, megabytes, gigabytes, terabytes, and petabytes. Supports both decimal SI units (1 GB = 1,000,000,000 bytes) and binary IEC units (1 GiB = 1,073,741,824 bytes) so you can match what storage vendors and operating systems report.

A 1 TB hard drive shows up as 931 GB in Windows. Your "1 GB" video clip is 1024 MB on macOS but 1000 MB on the package. The reason is the split between decimal SI units (used by storage manufacturers) and binary IEC units (used by operating systems). This converter handles both standards so you can reconcile any disk-size mystery.

Definition

The computation, step by step

1Enter the storage value you want to convert.
2Pick the source unit. Use KB/MB/GB for decimal (storage marketing) or KiB/MiB/GiB for binary (OS displays).
3Pick the target unit.
4The calculator converts to bytes first, then to the target unit.
5All other unit equivalents are shown below.

Solved example

A worked solution

Example: Why does a 1 TB drive show as 931 GB?

11 TB (decimal) = 1,000,000,000,000 bytes
2Windows divides by 1024³ = 1,073,741,824 bytes per "GB"
31,000,000,000,000 / 1,073,741,824 = 931.32 GiB

Result: A 1 TB drive holds 1 trillion bytes, which Windows displays as 931 GB (actually GiB).

Validity

Edge cases and pitfalls

Confusing GB with GiB: A 1 GB file (decimal) is 1,000,000,000 bytes. A 1 GiB file (binary) is 1,073,741,824 bytes. Operating systems labeled "GB" usually mean GiB. The difference grows at larger sizes.
Mixing bits and bytes in download speed: A "100 Mbps" connection delivers 100 megabits per second, or about 12.5 megabytes per second. Internet speeds are quoted in bits; file sizes in bytes.
Forgetting filesystem overhead: Even after the GB-vs-GiB issue, the formatted capacity is slightly less than the raw byte count. The filesystem uses some space for its own metadata.
Assuming MB always means 1024 KB: On Windows and macOS, MB usually means MiB (1024 KiB). On Linux, since 2010, MB means decimal (1000 KB) and MiB means binary. Always check which the source uses.

Adjacent topics

Related concepts

Term	Definition
Decimal (SI) units	1 KB = 1000 bytes, 1 MB = 1,000,000 bytes. Used by hard drive manufacturers and most network speeds.
Binary (IEC) units	1 KiB = 1024 bytes, 1 MiB = 1,048,576 bytes. Used by RAM specs and most operating systems.
Bit vs byte	A bit is one binary digit (0 or 1). A byte is 8 bits. Network speeds use bits per second; file sizes use bytes.

Applications

Where this calculation appears

Storage purchase planning: Compare advertised drive capacity with the actual usable space your OS will show.
Cloud backup sizing: Convert backup totals between MB, GB, and TB for service-tier matching.
Bandwidth and download estimates: Convert file sizes to bits for network speed calculations.
Database and log sizing: Convert row-size estimates from bytes up to MB or GB for capacity planning.

Implementation notes

Pro tips

Use bits per second for bandwidth: Network gear and ISPs use bits per second. Divide by 8 to get bytes per second. A 100 Mbps line tops out around 12 MB/s of actual file transfer.
Buy more than you think you need: After OS overhead and the GB-to-GiB difference, a "1 TB" drive gives you about 930 GB of usable space. Plan for 90% of the advertised capacity.
Use TB for video, GB for documents: Pick a unit that produces numbers between 1 and 999. "0.0034 TB" of documents and "3400 GB" of video are both readable; their reverses are not.
Verify by comparing to a known size: When a number looks wrong, compare to a known reference: 1 hour of HD video is about 1.5 GB, 1000 photos from a modern phone is about 4 GB.

Common questions

Frequently asked questions

Quick reference

Common Storage Sizes

Typical file and storage references

Item	Approx size	Bytes
Plain text email	2 KB	2,000
JPEG photo (12 MP)	5 MB	5,000,000
MP3 song (3 min)	4 MB	4,000,000
HD movie (90 min)	4 GB	4,000,000,000
4K movie (2 hours)typical	50 GB	50,000,000,000
1 TB SSD	1 TB	1,000,000,000,000

For related calculations, try the Number Base Converter, Length Converter, or Time Converter. Browse all Calculator Online calculators for the full catalog.

Methodology

This calculator uses the standard data storage converter formula. Results match those from established financial, scientific, and health references.

Reviewed by

Calculator Online Editorial Team. All formulas verified against authoritative sources before publication.

Last updated

2026-05-24