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Short answer: SSD manufacturers normally label capacity with decimal units: gigabytes (GB) and terabytes (TB). One GB is 1,000,000,000 bytes and one TB is 1,000,000,000,000 bytes. Binary units use gibibytes (GiB) and tebibytes (TiB): one GiB is 1,073,741,824 bytes and one TiB is 1,099,511,627,776 bytes. An operating system or application may count those same bytes in binary but display a familiar-looking GB or TB label, so a 1 TB SSD can appear as about 931 GiB or 0.909 TiB without any storage being missing.
The apparent discrepancy comes from two separate issues: decimal-versus-binary conversion, and space consumed by partitioning, formatting, reserved areas, or other software and device metadata. Unit conversion explains the first difference; it does not explain every byte that is unavailable for files.
The four units at a glance
GB and TB belong to the decimal, or SI-style, system. Their multipliers are powers of 10. GiB and TiB are IEC binary prefixes, whose multipliers are powers of 2. The prefixes describe how a byte count is expressed; they do not change the physical bytes in an SSD.
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| Unit | Full name | Number of bytes | Counting system | Where you commonly see it |
|---|---|---|---|---|
| GB | Gigabyte | 1,000,000,000 (109) | Decimal | SSD packaging and product specifications |
| GiB | Gibibyte | 1,073,741,824 (230) | Binary | Applications or operating-system tools that use IEC labels |
| TB | Terabyte | 1,000,000,000,000 (1012) | Decimal | SSD packaging and product specifications |
| TiB | Tebibyte | 1,099,511,627,776 (240) | Binary | Applications or operating-system tools that use IEC labels |
The National Institute of Standards and Technology (NIST) explains that the IEC binary prefixes were approved in December 1998 and are distinct from SI decimal prefixes. As NIST puts it: “It is important to recognize that the new prefixes for binary multiples are not part of the International System of Units (SI), the modern metric system.” NIST’s binary-prefix reference lists the byte values and the relationship between the two systems.
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Why a 1 TB SSD can look like 931 GB or 0.909 TiB
A decimal terabyte and a binary tebibyte are different-sized units. A manufacturer’s 1 TB label means exactly 1,000,000,000,000 bytes. To express that same byte count in binary units, divide by the binary unit:
- 1,000,000,000,000 ÷ 1,073,741,824 = approximately 931.32 GiB.
- 1,000,000,000,000 ÷ 1,099,511,627,776 = approximately 0.909 TiB.
Nothing has been removed in either conversion. The numeric value is lower because one GiB contains more bytes than one GB, and one TiB contains more bytes than one TB. GNOME’s documentation gives the practical example of a 1.0 TB drive appearing as 0.909 TiB. A capacity explanation from Seagate similarly describes a 1 TB drive appearing as roughly 931 gigabytes in a binary-counting display. In that context, the display may use the GB letters even though the arithmetic is binary, which is why the IEC names are useful.
How decimal and binary counting work
Decimal prefixes: GB and TB
Decimal units advance by factors of 1,000:
- 1 GB = 1,000 MB = 1,000,000,000 bytes.
- 1 TB = 1,000 GB = 1,000,000,000,000 bytes.
These are the units used for most storage product labels. A box or specification sheet that says “1 TB” is promising a decimal byte count, not 1,099,511,627,776 bytes.
Binary prefixes: GiB and TiB
Binary units advance by factors of 1,024:
- 1 KiB = 1,024 bytes.
- 1 MiB = 1,024 KiB.
- 1 GiB = 1,024 MiB = 1,073,741,824 bytes.
- 1 TiB = 1,024 GiB = 1,099,511,627,776 bytes.
The “i” in GiB and TiB signals the binary convention. Using those labels removes the ambiguity that occurs when software performs binary arithmetic but prints GB or TB.
The percentage difference
One decimal gigabyte is about 6.87% smaller than one GiB because 1,000,000,000 bytes divided by 1,073,741,824 bytes is approximately 0.9313. That is why a decimal capacity converted to GiB appears about 6.9% lower. At the terabyte scale, 1 TB is about 0.9095 TiB, so the displayed number is roughly 9.1% lower. These percentages describe unit size, not a manufacturing tolerance or a loss of NAND.
Which units SSD manufacturers use
Storage manufacturers commonly advertise SSD capacity in decimal GB and TB. Seagate describes decimal capacity as the storage-industry standard, and Verbatim’s capacity explanation explicitly covers SSDs while contrasting decimal product ratings with binary-style reporting. Therefore, a product sold as 500 GB, 1 TB, or 2 TB is normally specified using powers of 10.
The advertised number is a raw capacity convention, not a guarantee that every byte will be available in a newly installed volume. The drive may need partition tables, file-system structures, firmware-reserved space, over-provisioning, or other metadata. The amount consumed by those features depends on the device and software configuration; the cited capacity guidance does not provide one universal percentage for all SSDs.
Common capacity examples
| Decimal label | Approximate binary equivalent |
|---|---|
| 500 GB | 465.66 GiB |
| 1 TB | 931.32 GiB or 0.909 TiB |
| 2 TB | 1.819 TiB or 1,862.65 GiB |
| 4 TB | 3.638 TiB or 3,725.29 GiB |
These figures convert the advertised decimal bytes only. A formatted partition can be smaller, and a screen rounded to whole numbers may show a slightly different value.
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Which units operating systems and applications use
There is no single rule for every operating system, release, utility, and screen. Some interfaces use decimal calculations and labels; others use binary calculations, sometimes with IEC labels and sometimes with the older GB or TB labels. A historical explanation from Seagate discusses Windows and Mac reporting conventions, but it does not establish the behavior of every current release or every storage dialog.
GNOME System Monitor documents IEC labels—KiB, MiB, GiB, and TiB—for its memory and disk statistics. In a tool that follows that convention, the same bytes represented as a manufacturer’s 1 TB appear as approximately 0.909 TiB. Other tools may show a decimal value, or may show a binary value while retaining a decimal-looking label. Treat the label and the arithmetic as separate questions.
How to identify the convention in a particular screen
- Read the unit printed next to the value. “GiB” and “TiB” explicitly indicate binary units; “GB” and “TB” normally indicate decimal units, but older interfaces may use those labels loosely.
- Compare the displayed value with the manufacturer’s decimal capacity. A 1 TB device near 931 GiB is consistent with binary conversion; a value near 1,000 GB is consistent with decimal conversion.
- Check the utility’s documentation for its unit policy. GNOME, for example, documents IEC labels for its System Monitor statistics.
- Separate the unit conversion from volume layout. If the byte count is still substantially lower after accounting for decimal-versus-binary conversion, inspect partitions, formatting, reserved areas, and any recovery or vendor partitions.
Useful conversions and formulas
Start with the byte count when you need an unambiguous answer. The conversion formulas are:
- Decimal GB to GiB: GB × 1,000,000,000 ÷ 1,073,741,824.
- Decimal TB to TiB: TB × 1,000,000,000,000 ÷ 1,099,511,627,776.
- GiB to GB: GiB × 1,073,741,824 ÷ 1,000,000,000.
- TiB to TB: TiB × 1,099,511,627,776 ÷ 1,000,000,000,000.
For a direct byte calculation, multiply a decimal GB value by 1,000,000,000 or a decimal TB value by 1,000,000,000,000. Then divide by 230 for GiB or 240 for TiB. This method avoids rounding errors introduced by converting through an intermediate unit.
| Advertised decimal capacity | Same bytes expressed in binary units | Interpretation |
|---|---|---|
| 1 TB | Approximately 0.909 TiB, or 931.32 GiB | Expected decimal-to-binary conversion |
| 100 TB | 90.94 TiB | IBM’s documented conversion example |
IBM presents both unit systems in its storage documentation and notes that the numerical difference grows as capacities get larger. A conversion result should therefore be reported with its unit; saying only “1 TB equals 931” leaves out whether the number is GB, GiB, or something else.
Why usable capacity can be lower than the converted figure
Suppose a 1 TB SSD is displayed as about 931 GiB. That difference is explained by the unit system. If the operating system then reports a smaller usable volume, additional causes may be involved:
- Partition tables and file-system metadata reserve space.
- A recovery, diagnostic, or vendor partition occupies part of the drive.
- Firmware or the controller reserves NAND for maintenance and wear management.
- Formatting and allocation-unit structures reduce the space available for ordinary files.
- The displayed value may describe a partition or mounted volume rather than the entire physical device.
- Software may report decimal and binary values differently in separate screens.
These factors vary by SSD model, partition scheme, file system, and operating system. Capacity guidance from Seagate warns that several factors can affect reported capacity, so do not attribute every discrepancy to base-10/base-2 conversion alone. The figures above describe unit conversion, not a universal prediction of formatted free space.
A practical way to diagnose a capacity discrepancy
1. Confirm the product’s byte count
Read the SSD specification or label. A decimal rating such as 1 TB means 1,000,000,000,000 bytes. If the documentation states a different unit, use that stated unit rather than assuming.
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2. Determine whether the screen shows a device or a volume
Disk-management tools often list the physical drive, individual partitions, and mounted volumes separately. Compare like with like: the physical device’s capacity should be compared with the manufacturer’s rating, while a volume’s free space also reflects partitioning and file-system overhead.
3. Check the exact suffix
GiB and TiB are explicit binary labels. GB and TB are decimal labels under the SI convention, but a legacy interface can use them for binary arithmetic. If the label is ambiguous, calculate from bytes or consult the application’s documentation.
4. Account for layout and reserved space
Look for recovery partitions, unallocated regions, hidden metadata, and other reserved areas. Do not expect one fixed overhead percentage across all SSDs.
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5. Investigate only the remaining difference
After conversion and layout are accounted for, a much larger unexplained shortfall may justify checking partition tables, drive firmware, enclosure limits, or hardware health. Unit terminology by itself is not evidence that an SSD is defective.
Why the terminology matters when buying or planning storage
Use decimal TB and GB when matching an SSD to a product specification, a storage plan, or a backup target advertised in those units. Use GiB and TiB when estimating what a binary-counting tool will display. Keeping the unit attached to every number prevents planning errors.
- For an operating-system installation, compare the installer’s required GiB or GB value with the SSD’s converted capacity and leave room for partitions and updates.
- For backups, ensure the destination’s decimal capacity is larger than the source’s actual byte count, not merely equal in the printed unit.
- For arrays or pools, perform the calculation in bytes first, then convert the final result to the unit shown by the management software.
- When documenting a system, write values such as “1 TB (approximately 931 GiB)” instead of “1 TB/931 GB.”
Planning examples
If a backup application reports 700 GiB of data, a nominal 700 GB device is not large enough: 700 GiB requires about 751.62 GB of decimal capacity before any file-system or partition overhead. Conversely, a 1 TB SSD provides about 931.32 GiB of raw binary capacity, so a plan that requires 950 GiB needs a larger decimal drive. Always compare like units or convert both values to bytes.
Common misconceptions
“The manufacturer shorted me by about seven percent.”
Not when the comparison is decimal TB with binary GiB. A 1 TB label and an approximately 931 GiB display describe the same 1,000,000,000,000 bytes. The units are different sizes.
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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11“GB and GiB are interchangeable abbreviations.”
They are not. GB is decimal and GiB is binary. Some software has historically printed GB for a binary count, which creates ambiguity; the underlying multipliers remain different.
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“Every operating system uses binary units.”
Operating-system behavior varies by product, release, utility, and screen. GNOME documents IEC labels in System Monitor, while other interfaces may use decimal units or legacy labels. Verify the specific tool instead of generalizing across all systems.
“Unit conversion explains all missing usable space.”
It explains the difference between decimal and binary representations only. Partitions, formatting, reserved areas, and device-specific features can further reduce the volume available for files.
“A higher TB number always means more usable space.”
Only after the units and layout are compared consistently. A decimal 1 TB and a binary 1 TiB are not equal capacities: 1 TiB contains about 1.10 trillion bytes, more than a 1 TB product. Conversely, two drives with the same decimal label can expose different free-space figures after formatting and vendor partitions.
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Decimal prefixes such as kilo-, mega-, giga-, and tera- are part of the SI decimal system. The IEC binary prefixes Ki, Mi, Gi, and Ti were introduced to name powers of 2 without overloading those SI terms. NIST’s reference records the December 1998 approval and provides the exact byte values. IBM’s storage documentation uses the two systems side by side, including the 100 TB to 90.94 TiB example, to make the distinction explicit.
Using the correct prefix is more than pedantry. It tells a reader whether a number advances by 1,000 or 1,024 and makes capacity comparisons reproducible across product labels, operating-system tools, and technical documentation.
Bottom line for SSD owners
Read an SSD’s advertised TB or GB as decimal capacity. Read TiB or GiB as binary capacity. A 1 TB SSD contains 1,000,000,000,000 bytes, which is approximately 0.909 TiB or 931.32 GiB when expressed in binary units. If the usable volume is lower still, inspect partitions, formatting, reserved space, and the particular software’s reporting convention. The byte count is the stable reference; the displayed number depends on the unit system and the layer of storage being measured.
Frequently Asked Questions
Why does my 1 TB SSD show only about 931 GB?
The drive has 1,000,000,000,000 bytes, as advertised in decimal TB. A binary calculation divides those bytes by 1,073,741,824, producing about 931.32 GiB. Some interfaces label that binary result as GB, so the suffix can be misleading.
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Is 1 TB the same as 1 TiB?
No. One TB is 1,000,000,000,000 bytes; one TiB is 1,099,511,627,776 bytes. A 1 TiB device has about 10% more bytes than a 1 TB device.
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Do SSD manufacturers use GB or GiB?
They commonly use decimal GB and TB on packaging and specification sheets. Verbatim and Seagate describe decimal capacity as the storage-industry convention.
Which operating systems use GiB and TiB?
Behavior differs by operating system, release, utility, and screen. GNOME System Monitor documents IEC labels such as GiB and TiB. Other software may use decimal units or legacy GB/TB labels for binary calculations, so check the specific tool.
Why is my formatted volume smaller than 931 GiB?
The remaining difference can come from partition tables, recovery or vendor partitions, file-system metadata, formatting structures, firmware-reserved space, over-provisioning, or the screen measuring a volume rather than the whole device.
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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsHow can I convert a drive’s advertised TB to GiB?
Multiply the TB value by 1,000,000,000,000 and divide by 1,073,741,824. For example, 1 TB equals approximately 931.32 GiB. For TiB, divide the same byte count by 1,099,511,627,776.
Should I buy a larger SSD to compensate for the difference?
Choose capacity based on the byte requirement and leave room for partitions, updates, and normal free space. Convert the advertised decimal capacity to the unit used by your planning tool rather than adding an arbitrary percentage.
Does the lower displayed number mean the SSD is defective?
Usually not. A result near the expected decimal-to-binary conversion is normal. Investigate hardware or configuration only after checking the byte count, partition layout, reserved areas, and the software’s unit convention.
The Bottom Line
Bottom line: SSD labels are usually decimal: 1 TB equals 1,000,000,000,000 bytes. TiB and GiB are binary units, so that same drive is about 0.909 TiB or 931.32 GiB. Check the exact suffix and software documentation, then account separately for partitions, formatting, reserved space, and other layout overhead.
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