Short answer
- There are 1,000 GB in 1 TB. That is the decimal answer, and it is exact: 1 GB is 1,000,000,000 bytes, and 1 TB is 1,000,000,000,000 bytes, so a terabyte holds exactly one thousand gigabytes. If you are asking how many GB in a terabyte as that word is used on a drive box, a phone specification sheet, or a cloud storage plan, 1,000 is the answer. There is also a binary answer to a closely related question. In the binary system, the matching units are the gibibyte (GiB) and the tebibyte (TiB). There are 1,024 GiB in 1 TiB, exactly: 1 GiB is 1,073,741,824 bytes, and 1 TiB is 1,099,511,627,776 bytes. A tebibyte is a larger unit than a terabyte, by about 10 percent, so the two answers are not interchangeable. The practical consequence appears when the two systems meet. A drive sold as 1 TB holds 1,000,000,000,000 bytes. A program that counts those bytes in binary units divides by 1,073,741,824 and gets about 931.32 GiB, often displayed with the label GB. The drive has not lost anything: the same bytes, counted in a larger unit, give a smaller number. Every section below keeps the two systems separate and labels each figure, because mixing them inside a single figure is what makes this topic confusing.
By Emma Hudson
There are 1,000 gigabytes (GB) in 1 terabyte (TB) in the decimal system used on drive packaging, and 1,024 gibibytes (GiB) in 1 tebibyte (TiB) in the binary system many programs use to report size. Both answers are correct. The confusion around this question, and around drives that seem to lose capacity, comes from using the same letters for two different counting systems. This guide separates the two systems, gives full conversion tables for both, and works the common drive examples byte by byte.
The Two Systems Side by Side
Digital storage has two families of units. They look alike, they sound alike, and for small files the difference between them is easy to miss. They differ in one thing only: the size of each step up the scale.
The decimal family is the International System of Units, usually shortened to SI. Its prefixes, kilo, mega, giga, and tera, mean powers of 1,000 everywhere in science and engineering, and storage follows that meaning. Each step up multiplies by 1,000. A kilobyte is 1,000 bytes, a megabyte is 1,000 kilobytes, a gigabyte is 1,000 megabytes, and a terabyte is 1,000 gigabytes.
The binary family exists because computers work in powers of two. The step that sits closest to 1,000 in binary counting is 1,024, which is 2 to the power of 10. Each binary step up multiplies by 1,024. To keep the two families apart, the International Electrotechnical Commission, the IEC, approved a separate set of names and symbols for the binary units in December 1998, as the National Institute of Standards and Technology, NIST, explains in its guidance on prefixes for binary multiples. The binary names insert an i: kibibyte (KiB), mebibyte (MiB), gibibyte (GiB), and tebibyte (TiB). The i marks the unit as binary, so a reader can tell at a glance which system a figure belongs to.
NIST makes a second point worth holding on to. The binary prefixes are not part of SI. They were derived from the SI prefixes for ease of recall, but SI prefixes refer strictly to powers of ten. Writing GB for a binary quantity is therefore, strictly, a misuse of the symbol, even though the habit is widespread in software. GiB and TiB are exact and unambiguous. A bare GB or TB needs its context before you know which system it belongs to.
Full Decimal Table: KB Through TB
The decimal table below runs from the byte up through the petabyte, one step beyond the terabyte, so the pattern is visible in both directions. Every row is decimal. No binary figure appears in this table.
| Unit | Symbol | How many of the unit below | Bytes |
|---|---|---|---|
| Byte | B | Base unit | 1 |
| Kilobyte | KB | 1,000 bytes | 1,000 |
| Megabyte | MB | 1,000 KB | 1,000,000 |
| Gigabyte | GB | 1,000 MB | 1,000,000,000 |
| Terabyte | TB | 1,000 GB | 1,000,000,000,000 |
| Petabyte | PB | 1,000 TB | 1,000,000,000,000,000 |
Read the table in the direction you need. To convert down, from a larger unit to a smaller one, multiply by 1,000 at each step. One TB is 1,000 GB, 1,000,000 MB, and 1,000,000,000 KB. To convert up, divide by 1,000 at each step. Five hundred GB is 0.5 TB, because 500 divided by 1,000 is 0.5. Two thousand five hundred GB is 2.5 TB. The byte column is the check on any conversion: if the byte count does not match the row for the unit you land on, a step has been skipped or a step from the other system has crept in.
Decimal units are the units of sale and specification. Drive makers, memory card makers, and phone makers state capacity in decimal GB and TB, and Apple states the same convention in its support guidance: manufacturers measure storage capacity using the decimal system, base 10, and its product wording gives 1 GB as 1 billion bytes and 1 TB as 1 trillion bytes. Network speeds are decimal too, though quoted in bits rather than bytes.
Full Binary Table: KiB Through TiB
The binary table follows the same layout, so the two tables can be compared row by row. Every row is binary. No decimal figure appears in this table.
| Unit | Symbol | How many of the unit below | Bytes |
|---|---|---|---|
| Byte | B | Base unit | 1 |
| Kibibyte | KiB | 1,024 bytes | 1,024 |
| Mebibyte | MiB | 1,024 KiB | 1,048,576 |
| Gibibyte | GiB | 1,024 MiB | 1,073,741,824 |
| Tebibyte | TiB | 1,024 GiB | 1,099,511,627,776 |
| Pebibyte | PiB | 1,024 TiB | 1,125,899,906,842,624 |
The conversion rule mirrors the decimal rule with a different step size. To convert down, multiply by 1,024 at each step. One TiB is 1,024 GiB, 1,048,576 MiB, and 1,073,741,824 KiB. To convert up, divide by 1,024 at each step. Five hundred twelve GiB is 0.5 TiB, because 512 divided by 1,024 is 0.5. Two thousand forty eight GiB is 2 TiB.
Comparing the byte columns shows why labels matter more as units grow. At the first step the units are close: 1,000 bytes against 1,024 bytes. At the gigabyte step the comparison is 1,000,000,000 bytes against 1,073,741,824 bytes, a difference of more than 73 million bytes inside a single unit. At the terabyte step it is 1,000,000,000,000 bytes against 1,099,511,627,776 bytes, nearly 100 billion bytes inside a single unit. The measuring unit itself is larger, and the difference compounds at every step.
The Byte Counts, Worked Out
Formulas settle arguments that labels start. These are the core conversions of this article, each one worked in full so any of them can be checked with a calculator.
Decimal, staying inside one system: 1 TB = 1,000 GB. In bytes, 1 TB = 1,000 x 1,000,000,000 bytes = 1,000,000,000,000 bytes. That is 10 to the power of 12 bytes, one trillion bytes in the short scale naming used in the United States.
Binary, staying inside one system: 1 TiB = 1,024 GiB. In bytes, 1 TiB = 1,024 x 1,073,741,824 bytes = 1,099,511,627,776 bytes. That is 2 to the power of 40 bytes.
Crossing from decimal to binary: take the byte count, which belongs to neither system, and divide by the binary unit size. One TB in GiB is 1,000,000,000,000 divided by 1,073,741,824, which is 931.32 GiB when rounded to two decimal places. One TB in TiB is 1,000,000,000,000 divided by 1,099,511,627,776, which is about 0.909 TiB. One GB in GiB is 1,000,000,000 divided by 1,073,741,824, which is about 0.931 GiB.
Crossing from binary to decimal: divide the binary byte count by the decimal unit size. One TiB in GB is 1,099,511,627,776 divided by 1,000,000,000, which is 1,099.51 GB, or about 1.10 TB. One GiB in GB is 1,073,741,824 divided by 1,000,000,000, which is about 1.074 GB. One GiB in MB is 1,073,741,824 divided by 1,000,000, which is about 1,073.74 MB.
Two shortcut factors cover most everyday conversions. To turn decimal GB into GiB, divide by about 1.07374. To turn GiB into decimal GB, multiply by about 1.07374. At the terabyte level the factor is larger: divide decimal TB by about 1.09951 to get TiB, and multiply TiB by about 1.09951 to get decimal TB. Using the gigabyte factor at the terabyte level is a quiet source of wrong answers, because the two factors differ.
Why a 1 TB Drive Shows About 931 GiB
This is the worked example behind almost every version of this question, so it is worth doing slowly, in three steps, with no step hidden.
Step one: what the box promises. A drive sold as 1 TB is a decimal product. It holds at least 1,000,000,000,000 bytes, and many drives hold slightly more than the round figure. For this example, use exactly 1,000,000,000,000 bytes, the amount the label guarantees.
Step two: what a binary counting display does with those bytes. A display that counts in binary units asks how many gibibytes fit into the byte count. It divides 1,000,000,000,000 by 1,073,741,824, the number of bytes in 1 GiB. The result is 931.3226 GiB, which rounds to 931.32 GiB. If that display labels its binary units with the decimal symbols, as many displays historically have, the screen shows about 931 GB.
Step three: checking that nothing is missing. Multiply back: 931.32 GiB x 1,073,741,824 bytes per GiB gives back, allowing for rounding, the same one trillion bytes. Subtracting the displayed numbers, 1,000 minus 931.32, gives 68.68, but that subtraction mixes systems and has no physical meaning. One number counts the bytes in units of one billion; the other counts them in units of 1,073,741,824. A larger unit always produces a smaller count of the same quantity.
The same arithmetic at other common sizes is collected in this table. The first column is the decimal size as sold. The last column is the same bytes expressed in binary units.
| Drive as sold (decimal) | Bytes | Same bytes in binary units |
|---|---|---|
| 128 GB | 128,000,000,000 | About 119.21 GiB |
| 256 GB | 256,000,000,000 | About 238.42 GiB |
| 500 GB | 500,000,000,000 | About 465.66 GiB |
| 512 GB | 512,000,000,000 | About 476.84 GiB |
| 1 TB | 1,000,000,000,000 | About 931.32 GiB, or about 0.909 TiB |
| 2 TB | 2,000,000,000,000 | About 1,862.65 GiB, or about 1.819 TiB |
| 4 TB | 4,000,000,000,000 | About 3,725.29 GiB, or about 3.638 TiB |
| 8 TB | 8,000,000,000,000 | About 7,450.58 GiB, or about 7.276 TiB |
Each row is the same division: bytes divided by 1,073,741,824 for the GiB figure, and that result divided by 1,024 for the TiB figure. Spot check the 500 GB row: 500,000,000,000 divided by 1,073,741,824 is 465.66 GiB. Spot check the 4 TB row: 4,000,000,000,000 divided by 1,073,741,824 is 3,725.29 GiB, and divided by 1,024 that is 3.638 TiB. A real drive may sit a little above or below its row because it holds slightly more than the round byte count, or because formatting and system files have used some space, a separate and smaller effect covered below.
How the Gap Between the Systems Grows
The two systems drift apart because the step ratio, 1,024 divided by 1,000, is 1.024, and that ratio is applied again at every level. The drift is therefore not a fixed amount. It is a percentage that grows with the size of the unit.
At the kilobyte level, 1 KiB is 1.024 times 1 KB, so the binary unit is about 2.4 percent larger. At the megabyte level the ratio is applied twice, giving about 1.049, so 1 MiB is about 4.9 percent larger than 1 MB. At the gigabyte level it is applied three times, giving about 1.074, so 1 GiB is about 7.4 percent larger than 1 GB. At the terabyte level it is applied four times, giving about 1.100, so 1 TiB is about 10.0 percent larger than 1 TB, more precisely about 9.95 percent on the unrounded figures. At the petabyte level it reaches about 12.6 percent.
This growth explains the pattern people notice. A small file measured in kilobytes looks almost the same in either system. A folder measured in gigabytes differs enough to notice. A drive measured in terabytes differs by an amount that looks like a serious shortfall. The percentage was there all along; only the size of the quantity it applies to has changed.
How Different Contexts Report Size
The same storage can be reported in either system depending on where you look, which is why comparing figures from two different screens is risky without checking how each screen counts.
Drive and card packaging uses decimal units. That is the SI meaning of the prefixes, it is the convention Apple describes in its support guidance, and it applies to hard drives, solid state drives, USB drives, and memory cards alike. A 256 GB card holds 256,000,000,000 bytes before formatting, whichever device reads it.
Operating system displays vary. Some count in binary units and label the result GiB and TiB, which is exact. Some count in binary units and label the result GB and TB, which produces the familiar 931 figure for a 1 TB drive. Some count in decimal units, so the display matches the packaging closely. To tell which a display does, compare its byte count, if it shows one, with its headline figure: divide the bytes by the GB figure, and a result near 1,000,000,000 means decimal, while a result near 1,073,741,824 means binary, whatever label it uses.
File sizes follow the display that reports them, not the file. A file is a fixed number of bytes: one program may describe a 1,073,741,824 byte file as 1 GiB, another as about 1.07 GB. Download sizes quoted by a store or website are usually decimal, so a download described as 50 GB is 50,000,000,000 bytes, which a binary counting display describes as about 46.57 GiB needed. Check fit in the units of the receiving display.
Random access memory, RAM, is the main exception to the decimal rule for hardware. Memory is built in powers of two, because address lines double the number of locations they can address, so capacities land naturally on binary quantities. A module described as 8 GB of RAM is, in substance, 8 GiB, which is 8 x 1,073,741,824 = 8,589,934,592 bytes. A 16 GiB quantity is 17,179,869,184 bytes. Memory and drive figures that look comparable are therefore not directly comparable without conversion.
Phones and cloud plans add one more layer, because free space is not total capacity. A phone sold with 128 GB holds 128,000,000,000 bytes, about 119.21 GiB, and the operating system and built in applications use part of that space before your files are added, as Apple notes when it explains that formatting and the operating system use additional space. A cloud plan sold as 2 TB gives 2,000 GB of decimal quota, and a collection measured by a binary counting computer as 1,862.65 GiB is the same 2 TB. Compare like with like: bytes to bytes, or convert both sides into one system first.
Converting Between the Systems: Worked Examples
Four short examples cover the conversions readers ask for most. Each one states the system of the starting figure, converts through bytes, and states the system of the result.
Example one: a backup folder reported by a binary counting display as 500 GiB. In decimal terms: 500 x 1,073,741,824 = 536,870,912,000 bytes, divided by 1,000,000,000 gives about 536.87 GB. The same folder is 500 GiB and about 536.87 GB, and it uses about 536.87 GB of a decimal rated drive.
Example two: a photo library totaling 100 GB decimal. A binary counting display describes the same bytes, 100,000,000,000 divided by 1,073,741,824, as about 93.13 GiB. Nothing has been compressed or lost between the two screens.
Example three: a large file listed at 25 GB decimal by its publisher. In binary terms that is 25,000,000,000 divided by 1,073,741,824, about 23.28 GiB. Forty such files are 1,000 GB decimal, exactly 1 TB, and about 931.32 GiB binary.
Example four: counting files into a terabyte. If each photo file is 5 MB decimal, 5,000,000 bytes, then 1 TB holds 1,000,000,000,000 divided by 5,000,000, which is 200,000 such files, before formatting and other files. If each file is instead 5 MiB, 5,242,880 bytes, the count is 1,000,000,000,000 divided by 5,242,880, about 190,735 files. The answers differ only because the file size was stated in two systems.
Related Conversions From the Same Cluster
The neighbouring conversions follow the same two rules, so they can be answered without a separate method.
How many MB are in a GB? One thousand MB in the decimal system, because each decimal step is 1,000. One thousand twenty four MiB in 1 GiB in the binary system, because each binary step is 1,024.
How many GB are in a terabyte? This is the title question with the words in the other order, and the answer is unchanged: 1,000 GB in 1 TB decimal, and, in the binary pairing, 1,024 GiB in 1 TiB.
How many MB are in a TB? Multiply down two decimal steps: 1 TB is 1,000 GB, and each GB is 1,000 MB, so 1 TB is 1,000,000 MB. In binary, 1 TiB is 1,048,576 MiB.
How many KB are in a GB? Three decimal multiplications give 1 GB = 1,000 MB = 1,000,000 KB. In binary, 1 GiB = 1,024 MiB = 1,048,576 KiB.
How many bytes are in a TB and a TiB? One TB is 1,000,000,000,000 bytes. One TiB is 1,099,511,627,776 bytes. The difference between those two byte counts, 99,511,627,776 bytes, is itself about 99.51 GB decimal, which is why confusing the two units at this scale is never a rounding issue.
Buying and Comparing Storage Without Mixing Systems
Three habits prevent almost every storage misunderstanding at the point of purchase or comparison.
First, compare bytes when bytes are available. Byte counts are unambiguous, and specification sheets and drive property displays usually provide them. Two products with the same byte count hold the same amount, whatever units their marketing uses.
Second, if bytes are not available, compare only within one system. A drive quoted as 1,024 GiB holds 1 TiB, about 1.10 TB decimal, about 10 percent larger than a 1 TB drive. A drive quoted as 1,024 GB decimal holds 1.024 TB, only 2.4 percent larger than a 1 TB drive. The two headlines look identical and differ by more than 7 percent in real capacity, entirely because of the unit.
Third, plan capacity in the units of the device that will report it. If a computer reports free space in binary units labeled GB, treat its figures as GiB for planning: a collection listed as 100 GB decimal needs about 93.13 GiB of that reported space. Leave margin in any case, because formatting, system files, and updates use space the headline capacity does not set aside.
What Formatting and System Files Do and Do Not Explain
Two different effects reduce the space available on a new device, and they are often blamed on each other.
The larger effect is the counting difference explained above. It is not a loss at all. It appears the moment a decimal rated drive is read by a binary counting display, before a single file is written, and it accounts for about 68.68 of the numerical difference between 1,000 and 931.32 in the 1 TB example, in the sense that the whole of that numerical difference is the counting difference.
The smaller effect is real use of space. Formatting writes a file system structure that records where files are stored, and that structure occupies some capacity. An internal drive also holds the operating system, recovery data, and built in applications. Apple makes this point in the same guidance: actual formatted capacity is less, because formatting uses some storage space and additional space is used by the operating system. These amounts vary by device and file system, are usually far smaller than the counting difference at terabyte scale, and explain why available space is lower than even the correctly converted figure. They do not explain the gap between 1,000 GB and about 931 GiB, which is arithmetic, not consumption.
A practical check separates the two effects. Read the byte count for total capacity, not only the rounded figure. If the byte count is at least the decimal figure on the box, one trillion bytes for a 1 TB drive, the drive is the size it claims, and any lower headline number is counting or formatting. A byte count far below the labeled decimal figure would be a genuine shortfall worth raising with the seller.
Frequently Asked Questions
How many GB are in 1 TB?
One thousand GB in the decimal system used by drive manufacturers and on product packaging: 1 TB is 1,000,000,000,000 bytes, and 1 GB is 1,000,000,000 bytes. In the binary pairing, 1 TiB is 1,024 GiB.
How many GB are in a terabyte, exactly?
Exactly 1,000 decimal gigabytes. A tebibyte is a different and larger unit, not another name for a terabyte: 1 TiB is 1,099,511,627,776 bytes, against 1,000,000,000,000 bytes for 1 TB.
Is a TB 1,000 or 1,024 GB?
A terabyte is 1,000 GB. The 1,024 figure belongs to the binary pair: a tebibyte is 1,024 GiB. If a source says 1,024 without naming the unit, it is almost always describing GiB and TiB while using the shorter labels.
Why does my 1 TB drive show only about 931 GB?
Because the display is counting the same 1,000,000,000,000 bytes in binary gibibytes of 1,073,741,824 bytes each: 1,000,000,000,000 divided by 1,073,741,824 is about 931.32 GiB, labeled GB on that display. No storage is missing, and formatting explains only a further small amount, not this gap.
How many GiB are in 1 TB?
About 931.32 GiB. The full figure from the byte counts is 1,000,000,000,000 divided by 1,073,741,824, which is 931.3226 GiB before rounding.
How many GB are in 2 TB and 4 TB?
Two thousand GB in 2 TB and 4,000 GB in 4 TB, in decimal terms. In binary terms, 2 TB is about 1,862.65 GiB and 4 TB is about 3,725.29 GiB.
How many MB are in a GB?
One thousand MB in 1 GB in the decimal system. In the binary system, 1,024 MiB in 1 GiB. The two answers follow the same step sizes as the terabyte conversions, one level down.
How many bytes are in 1 TB?
One TB is 1,000,000,000,000 bytes, which is 10 to the power of 12 bytes. One TiB is 1,099,511,627,776 bytes, which is 2 to the power of 40 bytes.
Does RAM use the same units as drives?
Not in practice. Drives and cards are sold in decimal GB and TB. Memory is built in powers of two, so a quantity described as 8 GB of RAM is in substance 8 GiB, or 8,589,934,592 bytes. Convert before comparing memory and storage figures.
How do I convert GB to GiB quickly?
Divide the GB figure by about 1.07374. For example, 100 GB divided by 1.07374 is about 93.13 GiB, and 1,000 GB, which is 1 TB, divided by 1.07374 is about 931.32 GiB. To convert back, multiply the GiB figure by about 1.07374.
Why do two computers show different sizes for the same drive?
Because their displays count differently. One may report the drive in decimal units, giving a figure close to the packaging figure, while the other reports the same bytes in binary units, giving a smaller looking figure. Compare the byte counts the two displays show: they should agree, even when the GB figures do not.
Keep reading: How Many Seconds in an Hour? The Simple Answer, Worked Out
Sources & references
- National Institute of Standards and Technology (NIST), Definitions of the SI Units: The Binary Prefixes, and Prefixes for Binary Multiples. Used for the IEC binary prefixes approved in December 1998, for kibi, mebi, gibi, and tebi as powers of 1,024, for the examples 1 GiB = 1,073,741,824 bytes and 1 MB = 1,000,000 bytes, and for the point that the binary prefixes are not part of SI and were derived from the SI prefixes. https://physics.nist.gov/cuu/Units/binary.html
- Apple Support, How storage capacity is measured on Apple devices. Used for the statements that manufacturers of storage devices measure capacity using the decimal system (base 10), that product wording gives 1 GB = 1 billion bytes and 1 TB = 1 trillion bytes with actual formatted capacity less, that in binary measurement 1 GB = 1,073,741,824 bytes and 1 TB = 1,099,511,627,776 bytes on that page's binary wording, that some earlier Apple operating systems reported capacity using the binary system, and that formatting and the operating system use additional storage space. https://support.apple.com/en-ie/102119
