Why is my 1TB drive ~931 GB?
Drive makers count in decimal (1 TB = 10¹² bytes). Windows counts in binary (GiB = 2³⁰) but still writes “GB”.
| Advertised | Windows-style (GiB) | macOS (decimal) |
|---|---|---|
| 256 GB | 238.42 | 256 GB |
| 512 GB | 476.84 | 512 GB |
| 1 TB | 931.32 | 1 TB |
| 2 TB | 1862.65 | 2 TB |
How to use the Why is my 1TB drive ~931 GB?
What does the Why is my 1TB drive ~931 GB? do?
Convert advertised GB/TB to the size Windows shows; It applies this page-specific rule: hard-drive and SSD labels use SI decimal prefixes.
Which inputs does this tool use?
To convert advertised gb/tb to the size windows shows, enter Advertised size; keep every value in the same example; where available, choose between TB, GB to match the required format; select 256 GB when the values are ready; Start with a familiar case covered by this rule - Windows Explorer usually divides those same bytes by 1,073,741,824 (2³⁰) - so the expected result can confirm the settings.
How should the tool result be read?
For a result intended to convert advertised gb/tb to the size windows shows, windows Explorer usually divides those same bytes by 1,073,741,824 (2³⁰); read advertised size together with the original advertised size rather than as an isolated answer, and confirm that its units or structure match the intended use.
Is 69 GB actually missing?
When the goal is to convert advertised gb/tb to the size windows shows, no.
Why doesn’t my Mac show 931?
When using the page to convert advertised gb/tb to the size windows shows, modern macOS and iOS report decimal GB/TB, closer to the printed label (minus format overhead).
Limits and accuracy
When using this tool to convert advertised gb/tb to the size windows shows, macOS and iOS generally report decimal GB/TB, so the same disk can read as 1 TB there; check the result in its intended destination before relying on it for important work; keep advertised size until the output has been checked in its intended destination. For a repeatable check when you need to convert advertised gb/tb to the size windows shows, record Advertised size alongside the final output and selected options.
How this works
Hard-drive and SSD labels use SI decimal prefixes. One gigabyte on the box is 1,000,000,000 bytes. One terabyte is 1,000,000,000,000 bytes. That is what the factory measures when it prints “1TB”.
Windows Explorer usually divides those same bytes by 1,073,741,824 (2³⁰). The result is a mebibyte/gibibyte figure, but the window still says GB. 1,000,000,000,000 ÷ 1,073,741,824 ≈ 931.32. That is why a new 1TB disk often appears as 931 GB before you even create a partition.
macOS and iOS generally report decimal GB/TB, so the same disk can read as 1 TB there. If Explorer shows far less than the table on this page, look at partitions, recovery images, or the space the operating system already took - that is extra, not the unit mix-up.
This page does not “fix” missing space. It only translates the label into the number the operating system is likely to print.
Frequently asked questions
Is 69 GB actually missing?
No. Same bytes, two rulers. Decimal TB versus binary GiB.
Why doesn’t my Mac show 931?
Modern macOS and iOS report decimal GB/TB, closer to the printed label (minus format overhead).
Why does a 512 GB SSD show about 477 GB?
512 × 10⁹ ÷ 2³⁰ ≈ 476.84 GiB. Windows still labels that GB.
What about TiB?
1 TiB is 2⁴⁰ bytes. A labelled 1TB drive is about 0.9095 TiB.
Can I change Windows to decimal?
Not with a simple setting. Some third-party tools show both. This calculator is the translation.