The Number on the Box and the Number in File Explorer
You unbox a "1 TB" laptop, open File Explorer, and the drive says 931 GB. Nothing is wrong and nothing has been taken — the two figures count in different systems. The manufacturer sells capacity in gigabytes of exactly one billion bytes; Windows divides by 1 024 at every step, producing gibibytes, then prints the label "GB" anyway.
1 000 ÷ 1.073741824 = 931.32 GiB. That is the 931 your computer reports, from the very same 1 000 000 000 000 bytes.Two Different Gigabytes
Windows Shows GiB and Writes GB
The Gap Is Always the Same Share
Checking a New Drive or Phone in Under a Minute
Enter the Advertised Capacity
Type the number from the box in gigabytes. For a drive sold in terabytes use 1 000 per TB, so a 2 TB SSD goes in as 2000. Comma or dot both work and spaces are ignored.
Compare With What the Computer Reports
The gibibyte result is the figure Windows should be showing. Open the drive's properties, look at "Capacity", and the two should agree to within a rounding place.
Investigate Any Extra Shortfall
If the machine reports noticeably less than the converted figure, units are no longer the explanation — recovery partitions, a preinstalled system image or an already-populated drive account for the rest.
Keep the Figure for the Return Window
The copy button on either field gives the plain number, ready to paste into a support ticket or a note to yourself before the return period closes.
Working backwards: the swap button flips the direction and both fields accept typing, so you can enter the capacity your computer displays and see the marketing number behind it. Put 476.84 on the gibibyte side and the answer comes back as roughly 512 — the drive on the shelf you were looking at.
Advertised Capacity Against What Windows Displays
Every row is the same physical device described twice. The bytes column is what the hardware genuinely contains; the third column is that identical quantity in the 1 024-based units your computer uses, before a single file is written.
| Sold as | Bytes on the device | Shown by Windows | Apparent shortfall |
|---|---|---|---|
| 128 GB | 128 000 000 000 | 119.21 GiB | 8.79 |
| 256 GB | 256 000 000 000 | 238.42 GiB | 17.58 |
| 512 GB | 512 000 000 000 | 476.84 GiB | 35.16 |
| 1 TB | 1 000 000 000 000 | 931.32 GiB | 68.68 |
| 2 TB | 2 000 000 000 000 | 1 862.65 GiB | 137.35 |
| 4 TB | 4 000 000 000 000 | 3 725.29 GiB | 274.71 |
The shortfall doubles as the capacity doubles, because it is a fixed proportion rather than a fixed reserve. Bigger drives lose more in absolute terms — 274 on a 4 TB unit — which is why the complaint gets louder with every generation of larger disks.
Works for Phones and Cards Too
Memory cards, USB sticks and phone storage are sold in decimal gigabytes and reported in binary units, so the same conversion explains a 256 GB handset.
Shop From the Number You Already Have
Swap the direction, enter the capacity your current machine reports, and see which advertised size on the shelf matches the drive you are replacing.
Terabyte and Megabyte Sizes Included
The searchable dropdown on both sides carries TB and TiB, MB and MiB, so a 4 TB external or a 512 MB card needs no scaling by hand first.
Evidence for a Support Conversation
Convert, copy the bare figure and take it to the retailer's chat — a specific expected number moves things along faster than "it seems small".
What Buyers Ask About Missing Capacity
Is the manufacturer overstating the capacity?
No. A drive labelled 1 TB really does contain 1 000 000 000 000 bytes, and that matches the standard meaning of the prefix — a kilometre is a thousand metres, a terabyte a trillion bytes. The mismatch comes from the computer reporting those bytes in units of 1 024 while borrowing the decimal label. US class actions over exactly this settled on the same reading: the labelling is accurate, the display is what confuses people.
Where did the missing 69 GB go on a 1 TB SSD?
Nowhere — all 1 000 000 000 000 bytes are present and usable. Dividing them into 1 073 741 824-byte chunks yields 931.32 chunks instead of 1 000, and Windows calls each chunk a "GB". The 68.68 difference is a change of ruler, not a loss of storage. A few further gigabytes may go to filesystem tables and a recovery partition, but those are far smaller than the unit gap.
Why does my Mac report a bigger number than my PC for one drive?
macOS switched to decimal counting years ago, so it displays the capacity the box does: an external that reads 931.32 in Windows shows as 1 TB on a Mac. Neither is wrong and the drive has not changed — only the divisor. Linux desktops vary, with file managers usually reporting decimal GB while df -h defaults to binary units.
My phone says 256 GB but Settings shows far less available — why?
Two effects stack. The unit conversion takes 256 GB down to 238.42 in binary terms, then the operating system, preinstalled apps and system cache take their share — typically another 10 to 25 GB depending on the platform and how much the maker bundles. Storage that arrives already spoken for is normal; only a free figure dramatically below the table above is unusual.
Can reformatting or repartitioning give the space back?
Not the unit gap — no format changes how a byte count is divided for display. What you can sometimes reclaim is the extra: deleting a manufacturer recovery partition, removing a preloaded system image, or absorbing an unallocated block left by a previous install. That may return a handful of gigabytes on a laptop drive. The 68.68 on a 1 TB unit is arithmetic, and it stays.
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