iTechGuides is reader-supported. When you buy through links on our site, we may earn an affiliate commission. As an Amazon Associate I earn from qualifying purchases. Learn more
A drive sold as 1 TB contains 1,000,000,000,000 bytes, because storage manufacturers use decimal units. Divide that byte count by 1,073,741,824 bytes per binary gibibyte (GiB) and you get about 931.3 GiB. That conversion explains the familiar “smaller than advertised” figure; it does not predict the exact free space after formatting, partitions, the operating system and your files are accounted for.
Use the calculation below to compare SSD labels on a consistent basis, then treat formatted capacity and free space as separate planning questions.
Why an SSD appears smaller than its label
Storage labels and computer displays can use different unit systems. SSD manufacturers state capacity in decimal bytes:
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errors- 1 GB means 1,000,000,000 bytes.
- 1 TB means 1,000,000,000,000 bytes.
Binary units are based on powers of 1,024 instead:
- 1 GiB equals 1,073,741,824 bytes.
- 1 TiB equals 1,099,511,627,776 bytes.
Apple Support’s February 26, 2025 explanation states that storage manufacturers measure capacity using the decimal system. Apple also distinguishes decimal GB and TB from their binary counterparts. Seagate Support gives the common example that a 1 TB drive can be reported at about 931 GB; that displayed “GB” is approximately 931 binary GiB, even when the interface uses the familiar GB label.
#1 Best Overall
- Ideal for high speed, low power storage
- Gen 4x4 NVMe PCle performance
- Up to 6,000MB/s read, 4,000MB/s write
- Includes Acronis cloning software
- 5-year limited warranty
Nothing has vanished from the device. The same number of bytes is being expressed against a larger binary unit. A computer that reports roughly 931 for a drive marked 1 TB is normally showing the expected unit conversion before other storage is consumed.
The exact conversion to use before buying
Formula
Convert an advertised decimal capacity to binary GiB with:
binary capacity in GiB = advertised capacity in bytes ÷ 1,073,741,824
Quick wins for a faster PC:
Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Repair Windows errors before they cause bigger problemsFix Now →For a 1 TB SSD:
- Start with the advertised decimal value:
1,000,000,000,000bytes. - Divide by the number of bytes in one GiB:
1,073,741,824. - The result is approximately 931.3 GiB.
This is a unit conversion, not a manufacturer-specific deduction. It applies the same way to every drive whose label uses decimal capacity.
Why some screens still say GB
Some operating-system interfaces display binary quantities while labeling them GB or TB. That practice makes a value such as 931 look as though it is a decimal gigabyte figure, even though it is close to 931 GiB. Operating systems do not all label units identically, so identify the unit basis before comparing a screen value with a retail label.
Rank #2
- This product has been replaced by our latest generation. Please search for the SANDISK Optimus GX 7100 NVMe SSD
- HIGH-OCTANE GAMING. Experience speeds up to 7,250MB/s read and 6,900MB/s write (1-2TB models), with up to 35% faster performance than previous generation.
- PURPOSE-BUILT. Designed for serious on-the-go gamers, with a PCIe Gen4 interface and SANDISK’s next generation TLC 3D NAND.
- MORE TIME TO CLEAR THAT CHECKPOINT. Built with laptops and handheld gaming devices in mind, with up to 100% more power efficiency over the previous generation.
- DO MORE WITH DASHBOARD. Ensure your drive is optimized for prime performance with the downloadable WD_BLACK Dashboard (Windows only).
Reference conversions for common SSD labels
The following figures are calculated from the decimal byte labels and show the binary equivalent before formatting or partition allocation. Values are rounded to two decimal places.
| Advertised label | Decimal bytes | Approximate binary capacity |
|---|---|---|
| 250 GB | 250,000,000,000 | 232.83 GiB |
| 500 GB | 500,000,000,000 | 465.66 GiB |
| 1 TB | 1,000,000,000,000 | 931.32 GiB |
| 1.5 TB | 1,500,000,000,000 | 1,396.98 GiB |
| 2 TB | 2,000,000,000,000 | 1,862.65 GiB |
| 4 TB | 4,000,000,000,000 | 3,725.29 GiB |
For a quick estimate, multiply a decimal GB figure by approximately 0.9313 to obtain GiB. Thus 500 GB is about 465.7 GiB, while 2,000 GB (2 TB) is about 1,862.6 GiB. The division formula is preferable when you need a precise result or are working from a byte count.
What the conversion tells you—and what it cannot tell you
What it tells you
- The binary equivalent of the byte capacity printed on the box or product page.
- Why a nominal 1 TB SSD is shown near 931 in many disk utilities.
- A consistent basis for comparing 500 GB, 1 TB, 2 TB and other capacity options.
What it does not tell you
- The exact size of a formatted volume.
- How much space the operating system and its partitions will occupy.
- The size of recovery or other system partitions created during installation.
- How much free space remains after applications, documents, media and other files are stored.
Apple notes that formatting uses some storage. The operating system, its system and recovery partitions, the chosen partition layout and files already on the drive also change the number you can use. There is no single formatting percentage that applies to every SSD, operating system or installation. Therefore, 931.3 GiB is a pre-format binary equivalent, not a guaranteed free-space figure.
A step-by-step pre-purchase calculation
1. Record the label exactly
Write down the capacity as advertised, including whether it is expressed in GB or TB. Storage labels normally use decimal notation, so treat 1 TB as 1,000,000,000,000 bytes and 1 GB as 1,000,000,000 bytes unless the specification explicitly says otherwise.
2. Convert the label to GiB
For a TB label, multiply by 1,000,000,000,000 bytes per decimal TB and divide by 1,073,741,824. For a GB label, multiply by 1,000,000,000 bytes per decimal GB and divide by the same divisor. Keep at least one decimal place while comparing drives; rounding to a whole number can hide small differences.
Rank #3
- Solid state performance with up to 800MB/s read speeds in a portable drive. (Based on internal testing; performance may be lower depending on host device, interface, usage conditions and other factors. 1MB=1,000,000 bytes.)
- Back up your content and memories on a storage solution that fits seamlessly into your mobile lifestyle.
- Take it with you on your adventures—up to two-meter drop protection means this durable drive can take a beating. (Based on internal testing.)
- Secure it to your belt loop or backpack for extra peace of mind thanks to the tough rubber hook.
- From Sandisk, a brand professional photographers trust to take on assignments.
3. Separate capacity from setup overhead
Put the calculated GiB figure in one column of your notes. In a separate column, list the operating system, applications, recovery tools, planned files and any other data that must fit. Do not subtract an invented universal formatting allowance. The setup determines the actual deduction, and the reviewed manufacturer guidance does not establish one fixed amount.
4. Compare options on the same axis
Apply the same conversion to every candidate. Comparing one drive’s decimal TB label with another drive’s binary GiB display makes the second drive appear unfairly smaller. A useful comparison table has at least these columns:
| Drive label | Advertised decimal capacity | Calculated binary equivalent | Setup-specific information still needed |
|---|---|---|---|
| Example: 500 GB | 500,000,000,000 bytes | About 465.66 GiB | Formatting, partitions and stored data |
| Example: 1 TB | 1,000,000,000,000 bytes | About 931.32 GiB | Formatting, partitions and stored data |
| Example: 2 TB | 2,000,000,000,000 bytes | About 1,862.65 GiB | Formatting, partitions and stored data |
5. Check your requirement against the result
Use the binary equivalent as the starting capacity for planning, then verify that your operating system, applications and files fit with room for growth. The calculation helps you choose between labels; it cannot decide how much headroom your workload needs. If your estimate is close to the requirement, choose the next capacity tier rather than assuming every byte shown by the conversion will be free after installation.
Understanding formatted capacity and free space
Three numbers are easy to confuse:
- Advertised capacity: the manufacturer’s decimal byte count, such as 1,000,000,000,000 bytes for 1 TB.
- Formatted or allocated capacity: the space exposed by a partition or volume after the file system and the installation layout are created.
- Free space: the portion of that formatted volume not occupied by the operating system, applications, recovery data and your files.
The first number is fixed by the label. The second depends on formatting and partitioning. The third changes whenever data is added or removed. A buyer who asks for “usable capacity” should therefore decide which of the latter two numbers is needed. For a pre-purchase comparison, calculate the binary equivalent first; for a deployment plan, inspect the intended operating-system layout and add the data that will be stored.
For example, a 1 TB label converts to about 931.3 GiB. After installation, the visible volume can be lower because the disk is formatted and because system or recovery partitions are present. Once files are copied, the remaining free-space figure will be lower again. None of those later changes means the original decimal byte label was inaccurate.
Free tools Windows power users keep installed
One-click scans. No signup required.
Rank #4
- HUGE SPEED BOOST: Get random read/write speeds that are 40%/55% faster than 980 PRO; Experience up to 1400K/1550K IOPS, while sequential read/write speeds up to 7,450/6,900 MB/s reach near the max performance of PCIe 4.0*
- BREAKTHROUGH POWER EFFICIENCY: Use less power and get more performance; Enjoy up to 50% improved performance per watt over 980 PRO, plus optimal power efficiency with max PCIe 4.0 performance**
- SMART THERMAL CONTROL: Samsung's own nickel-coated controller delivers effective thermal control; With its slim size, 990 PRO is a perfect fit for desktops and laptops that meet the PCI-SIG D8 standard***
- THE CHAMPION MAKER: Up to 65% improvement in random performance enables faster loads for an ultimate gaming experience on PS5 and DirectStorage PC games****
- SAMSUNG MAGICIAN SOFTWARE: Get the most out of your SSD with Samsung Magician's advanced yet intuitive optimization tools; Monitor drive health, protect valuable data, and receive important updates for your 990 PRO
How to interpret an installed drive that looks too small
First, check the unit basis
If the disk utility reports roughly 931 for a 1 TB SSD, the decimal-to-binary difference is the likely explanation. Confirm whether the utility is showing GB, GiB, TB or TiB, and whether it uses a familiar label for a binary quantity.
Next, inspect the disk and volume layout
Open the operating system’s disk-management utility and view the physical disk, each partition and any unallocated area. Compare the total disk size with the volume size. A volume can be smaller than the physical disk when space is reserved for system or recovery partitions or has not been assigned to a volume.
Check whether all capacity is allocated
If unallocated space is visible, the missing capacity is not explained solely by decimal versus binary units. The partition layout may need to be adjusted using the operating system’s documented tools, with a backup made before changing partitions. Do not delete a recovery or system partition merely to make a number look larger; those partitions can be required for repair or boot functions.
Account for formatting and existing files
Compare the formatted volume with the raw disk and then check which files already occupy it. Formatting, the operating system, recovery data and stored files are separate deductions from the unit conversion. Their sizes vary by installation, so a fixed percentage cannot be used as a universal test.
Escalate only after those checks
If the physical disk’s reported byte capacity is substantially below what the decimal label predicts after the unit basis and layout are understood, consult the drive maker’s support documentation and the retailer’s return process. The decimal/binary conversion explains the normal difference, not every possible hardware, partitioning or installation problem.
Best Value
- High-Efficiency Performance: The SSD 1TB SATA adopts 3D NAND flash memory, which achieves a read speed of up to 560MB/s and a write speed of up to 510MB/s. Get a faster data transfer experience and improve your work efficiency.
- Upgrate Your Computer: The SATA 1TB SSD achieved faster app load and response times, and faster boot-up and shut-down, compared to HDDs. The internal SSD adopts advanced SLC Cache Technology, which improves overall computer performance.
- Reliability and Stability: The 2.5 SSD 1TB supports garbage collection, advanced wear-leveling technology, RAID, ECC, TRIM, and S.M.A.R.T, which makes the SATA SSD more reliable and stable. With the characteristics of shockproof, the SSD hard drive can keep your data safe, without worry even if your computer drops.
- Wide Compatibility: The 2.5'' SSD built-in SATA III 6Gb/S interfaces, witch backwards compatible with SATA II and SATA interfaces. The Internal SATA SSD is compatible with Windows, Linux, and Mac OS, and compatible with laptops, desktops, and all-in-one computers.
- 3-Year Service: Our SSDs come with a 3 years after-sales service and lifetime technical support. If you have any questions, please contact us and we will sincerely and professionally solve the problem for you.
Common calculation mistakes
Calling 931 GiB “931 decimal GB”
In everyday interfaces, 931 may be labeled GB, but the value is approximately 931 GiB when derived from a 1 TB decimal label. State the unit basis whenever precision matters.
Using 1,000,000,000 instead of 1,073,741,824 as the divisor
Dividing by 1,000,000,000 simply returns decimal gigabytes. To convert bytes to binary GiB, use 1,073,741,824.
Subtracting a made-up formatting percentage
Formatting and partitions vary. A percentage copied from one computer is not a guaranteed deduction for another. Keep the conversion and the setup estimate as separate calculations.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
Confusing capacity with free space
A new drive’s formatted volume is not the same as its eventual free space. The operating system, applications, recovery data and personal files all consume space after installation.
Comparing unlike units
Compare decimal label to decimal label, or convert every label to GiB before comparing. Do not compare a manufacturer’s 1 TB with a utility’s 931 GB without identifying how the utility defines GB.
Using official definitions to explain the difference
Apple Support’s February 26, 2025 article provides both sets of definitions: decimal 1 GB equals 1 billion bytes and decimal 1 TB equals 1 trillion bytes; binary 1 GB in its binary-unit explanation equals 1,073,741,824 bytes and binary 1 TB equals 1,099,511,627,776 bytes. Apple’s wording is direct: “Manufacturers of storage devices measure storage capacity using the decimal system (base 10).”
Seagate Support uses the practical 1 TB-to-about-931 example, while Intel Support explains that an SSD’s label capacity is decimal and that operating systems normally indicate less than the label. These statements describe unit conventions and installation effects, not a promise that every computer will show exactly the same formatted or free-space number.
The Tool Desk
Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →A compact worksheet you can reuse
- Advertised label: write the decimal GB or TB value.
- Byte count: convert GB to GB value × 1,000,000,000, or TB to TB value × 1,000,000,000,000.
- Binary estimate: divide the byte count by 1,073,741,824 to obtain GiB.
- Installation plan: list the operating system, applications, recovery layout and files separately.
- Decision: select a capacity whose calculated GiB leaves room for that plan; do not treat the conversion as guaranteed free space.
- After installation: if the disk seems unexpectedly small, verify units, inspect partitions and unallocated space, and account for formatting and existing files.
Following those six entries keeps the predictable unit difference separate from setup-specific storage consumption. It gives you a defensible estimate before purchase without claiming a universal formatted-capacity deduction.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
