Convert terabytes to tebibytes

Content last reviewed:2026-09-30

A 4 TB drive holds 3.638 TiB, because the maker counts a terabyte as a trillion bytes while a tebibyte is 1,099,511,627,776 bytes. Type the capacity from the drive label and the converter gives it in tebibytes, the unit Windows and most NAS boxes actually use when they report space.

Terabytes

Tebibytes

TiB

What is the difference between a terabyte and a tebibyte?

A terabyte (TB) is a trillion bytes, or 10¹² B. A tebibyte (TiB) is 2⁴⁰ bytes, which comes to 1,099,511,627,776 B, so it is 9.95% bigger. The International Electrotechnical Commission (IEC) defined the binary prefixes with an “i” in the symbol, such as gibi and tebi, in 1999, so that powers of two would no longer borrow the metric prefixes[1]. The SI Brochure of the International Bureau of Weights and Measures (BIPM) backs this up: kilo, mega and tera stand strictly for powers of ten, so a kilobit is 1000 bits, and the binary prefixes are the ones to use for powers of two[2].

Both units describe the same drive; they just count its bytes differently. Manufacturers state capacity in decimal, so 4 TB on the box means four trillion bytes[3]. Windows divides that byte count by powers of 1,024 but still labels the result TB[1]. That is why a brand-new 4 TB drive shows up in File Explorer as roughly 3.6 TB, even though not a single byte is missing. On a Mac the same drive reads 4 TB, because macOS, like Ubuntu and Debian, reports capacity in decimal units[1].

Two Western Digital WD40PURZ hard drives with 4TB printed on the label — Both Western Digital WD40PURZ drives carry a 4TB capacity on their labels. Once connected, each one holds 3.638 TiB, which Windows displays as about 3.6 TB. Photo: 0xk, Unsplash.

How do you convert TB to TiB? Formula and Excel

Multiply the terabytes by a trillion to get bytes, then divide by 2⁴⁰. As a shortcut, multiply the terabytes by 0.9094947:

TiB = TB × 10¹² ÷ 1,099,511,627,776,
TiB ≈ TB × 0.9094947.

A 16 TB drive therefore holds 16 × 0.9094947, or 14.5519 TiB. The multiplier is the same for every size, so a bigger drive loses more gigabytes on screen while the percentage gap stays fixed.

In Excel, use =CONVERT(A2,"Tbyte","Tibyte"), where the prefix “Ti” stands for tebi, or 2⁴⁰[4]. To go the other way, open the TiB to TB converter. For gigabytes with a choice of decimal or binary counting, use the TB to GB converter. To turn label gigabytes into gibibytes, use the GB to GiB converter.

How many TiB does a drive of each size hold?

The capacity printed on the drive, converted to tebibytes. Windows shows roughly this figure, although it labels it TB.

Capacity on the label	Tebibytes
1 TB	0.9095 TiB
2 TB	1.819 TiB
4 TB	3.638 TiB
6 TB	5.457 TiB
8 TB	7.276 TiB
10 TB	9.0949 TiB
12 TB	10.9139 TiB
14 TB	12.7329 TiB
16 TB	14.5519 TiB
18 TB	16.3709 TiB
20 TB	18.1899 TiB
22 TB	20.0089 TiB
24 TB	21.8279 TiB
26 TB	23.6469 TiB
28 TB	25.4659 TiB
30 TB	27.2848 TiB
32 TB	29.1038 TiB

The table gives the size of the whole drive. After formatting you will see a little less free space, because the file system takes up part of the drive[3].

Why does my 4 TB drive only show 2 TB?

This happens when the drive uses the MBR partition table. MBR stores the sector number in 32 bits, so with 512-byte sectors it can reach at most 2³² × 512 B, which is 2 TiB. Microsoft calls this limit “2 TB” but notes that it counts in powers of two, and that the matching drive label reads about 2.2 TB[5].

On a 3 TB or 4 TB drive set up as MBR, Windows can only create partitions in the first 2 TiB, and the rest of the capacity cannot be used[5]. The fix is to initialise the drive as GPT, which addresses the full capacity, and Microsoft advises backing up important data first. If you want the computer to boot from that drive, its firmware has to support UEFI[5].

How many TiB will a multi-drive NAS show?

A Synology NAS reports capacity under Storage Manager > HDD/SSD using binary counting, so drives look smaller there than on the label[6]. The table shows how much room for data a common set of drives gives you, first in terabytes and then in tebibytes.

Drives and RAID type	Space for data	In tebibytes
2 × 4 TB, RAID 1	4 TB	3.638 TiB
2 × 8 TB, RAID 1	8 TB	7.276 TiB
4 × 4 TB, RAID 5	12 TB	10.9139 TiB
4 × 8 TB, RAID 5	24 TB	21.8279 TiB
4 × 16 TB, RAID 5	48 TB	43.6557 TiB
6 × 20 TB, RAID 6	80 TB	72.7596 TiB
8 × 24 TB, RAID 6	144 TB	130.9672 TiB

Space for data follows Synology's formulas: a two-drive RAID 1 gives you the capacity of one drive, RAID 5 the capacity of all drives but one, and RAID 6 all drives but two[7]. The missing capacity holds a copy of the data in RAID 1 or parity data in RAID 5 and RAID 6, which lets the array survive the failure of one or two drives[7].

Which ways of writing terabytes does this converter accept?

Paste the capacity the way you have it: with a decimal point, with thousands separators, or together with the symbol and the drive name from a shop listing. The field reads each of these and converts it for you, and the converter itself worked out every result in the table.

What you type	What the converter shows	How we read it
3.5	3.1832 TiB	The dot is the decimal point, so the field holds three and a half terabytes.
3,5	3.1832 TiB	A comma before one digit can only be a decimal comma, as used across Europe, so the result matches 3.5.
1,500	1364.2421 TiB	A comma before three digits is a thousands separator, so the field counts fifteen hundred terabytes. A note under the field says so; type one and a half as 1.5.
1.500	1.3642 TiB	A single dot is always read as a decimal point, so the field counts one and a half terabytes. A note under the field says so; type fifteen hundred as 1500 or 1,500.
½	0.4547 TiB	A ½ character copied from text counts as half a terabyte.
1e3	909.4947 TiB	Scientific notation from a spreadsheet is read as written, so 1e3 is a thousand terabytes.
16TB	14.5519 TiB	The TB stuck to the number is dropped and the field counts sixteen terabytes.
Capacity: 18 TB	16.3709 TiB	From a line copied out of a shop listing we take only the number next to the symbol.
WD40PURZ 4TB	3.638 TiB	The digits in the model name are not merged with the capacity, so the field counts the 4 TB from the label.
500 GB	0.4547 TiB	Gigabytes pasted into the terabyte field are written in as 0.5 TB, with a note under the field.
3.64 TiB	3.64 TiB	Tebibytes pasted into the terabyte field, say from a NAS window, are written in as 4.002222 TB, so the result comes back to 3.64 TiB.
4,000,787,030,016 bytes	3.6387 TiB	The byte count from the Properties window of a 4 TB drive becomes 4.000787 TB in the field, with a note under it.

Convert Terabytes to other units

TB to GB TB to PB

Sources

Binary prefix — Wikipedia
The International System of Units (SI), 9th edition — BIPM
How storage capacity is measured on Apple devices — Apple
CONVERT function — Microsoft
Windows support for hard disks exceeding 2 TB — Microsoft
Why does my drive size appear smaller on Synology storage system? — Synology
Choose a RAID Type — Synology

Every figure in the tables was computed from the unit definitions and checked arithmetically before publication. Historical values and the names of local units come from the sources listed above.

Content last reviewed: September 30, 2026 · written and checked by the Arteon team

Frequently asked questions about terabytes and tebibytes

Does an SSD also show less space than the label says?

Yes. Manufacturers state the capacity of every storage device in decimal, SSDs included[3], so a 2 TB SSD holds 1.819 TiB and Windows shows it as about 1.8 TB.

Do two 4 TB drives in RAID 1 give me 8 TB?

No. RAID 1 writes the same data to both drives, so you get the space of one drive, 4 TB[7]. The NAS will show about 3.6 TB of it, because it reports tebibytes.

Arteon free tool screenshot: Convert terabytes to tebibytes

Have a question or suggestion?

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