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Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →A 1TB SSD can appear as about 931GB because the drive label and the computer may count the same bytes using different unit systems. That conversion alone does not mean the drive is defective or short-shipped. Formatting and system files can reduce the space available for your files further, but that is a separate cause.
Why does a 1TB drive show about 931GB?
Drive makers use decimal units: 1 terabyte (TB) is 1,000,000,000,000 bytes. Some operating-system capacity calculations use binary-sized units, in which one gigabyte is 1,073,741,824 bytes. Divide the drive’s advertised byte count by that larger unit and the result is about 931.32 binary gigabytes, properly called gibibytes (GiB). Some software labels this binary-derived figure “GB.”
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Intel describes SSD labels as decimal and says most operating systems calculate capacity in binary notation in its support article, last reviewed November 8, 2022. That is a generalization, not a guarantee about every operating system, version, or screen. Apple’s February 2025 explanation likewise defines 1 TB as one trillion bytes and notes that some older Apple software reported capacity in binary units.
Compare the bytes, not just the labels
| Capacity expression | Meaning |
|---|---|
| 1 TB | 1,000,000,000,000 bytes (decimal) |
| 1 GiB | 1,073,741,824 bytes (binary) |
| 1 TiB | 1,099,511,627,776 bytes (binary) |
| 1,000,000,000,000 bytes ÷ 1,073,741,824 | About 931.32 GiB; software may label the result GB |
| 1,000,000,000,000 bytes ÷ 1,099,511,627,776 | About 0.9095 TiB |
So “1 TB” and “931 GB” are not necessarily competing measurements in the same unit. They can describe the same byte count using differently sized units. Intel’s worked example gives about 931.32 GB for a 1TB label under binary conversion. For a larger example, Intel calculates that 2TB converts to about 1.81898940… binary TB (TiB) in its article last reviewed March 16, 2022.
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Why the space available for files can be lower still
The unit conversion accounts for the apparent change in the displayed number; it does not account for every byte that cannot be used for personal files. Formatting and operating-system storage also take space. Apple explicitly notes that actual formatted capacity is lower than the stated capacity. The amount can depend on the device and its setup, so the unit conversion alone cannot tell you how much space a particular installation will leave free.
How to check whether the difference is just the units
- Find the capacity measure you are comparing. A drive’s advertised capacity is its decimal byte count. A computer may show total device capacity, a partition’s capacity, formatted capacity, or free space for files; those are not interchangeable.
- Look for the exact byte count if your system exposes it. Compare that count with 1,000,000,000,000 bytes for a nominal 1TB drive. A display near 931GiB can be consistent with the same nominal capacity when binary units are used.
- Separate total capacity from available space. If the figure is free space rather than the whole drive or partition, formatting and system storage can account for some of the difference.
- Investigate a larger unexplained gap separately. These unit definitions do not diagnose a specific drive, partition layout, system-reserved allocation, firmware issue, or hardware fault. Compare the same capacity measure and exact byte counts before deciding that capacity is missing.
Why the naming mismatch developed
Seagate’s guide explains that computer professionals historically used “kilo” for 1,024 because it was close to 1,000. As computing reached a broader audience, that usage conflicted with the familiar decimal meaning of the prefix. The binary names GiB and TiB distinguish powers-of-two units from decimal GB and TB, but software and everyday usage have not always made that distinction visible.
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Will this remain a problem forever?
“Forever” goes further than the evidence supports. Mixed unit conventions and displays have persisted, so the confusion is likely to continue as long as some capacity labels use decimal units and some software reports binary-derived values under familiar decimal labels. That is a conditional expectation, not proof that the mismatch can never be resolved.
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Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →For the official explanations, see Apple’s storage-capacity guide, Intel’s SSD size explanation, Seagate’s capacity measurement guide, and Intel’s 2TB conversion example.
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