Why does my 1 TB hard drive only show 931 GB?

The maker counts 1 TB as 1,000,000,000,000 bytes, while Windows divides by 1,073,741,824 per GB and still labels it GB. 1,000,000,000,000 divided by 1,073,741,824 is 931.32.

Is 1 GB 1,000 MB or 1,024 MB?

Both are used. In decimal units 1 GB is 1,000 MB; in binary units, which Windows uses, it is 1,024. The binary unit is officially called a gibibyte (GiB).

How do I convert Mbps to MB per second?

Divide by 8. 100 Mbps is 12.5 decimal megabytes per second, or about 11.92 binary megabytes per second.

Does the Data Storage Converter use 1,000 or 1,024?

Its KB, MB, GB, TB and PB units are binary (1,024-based), while its Kilobit, Megabit and Gigabit units are decimal, as network speeds normally are.

Why Does a 1 TB Drive Show 931 GB? Binary vs Decimal Explained

The short answer

A 1 TB drive shows about 931 GB in Windows because the manufacturer counts 1 TB as 1,000,000,000,000 bytes, while Windows divides by 1,024 three times and still calls the result "GB". Nothing is missing: 1,000,000,000,000 ÷ 1,073,741,824 = 931.32. You can check any capacity in the Data Storage Converter by entering the advertised size in bytes and converting to GB.

Two meanings of "GB"

Storage sizes are written with the same letters but two different number systems.

Name	Symbol	Bytes
Kilobyte (decimal)	kB	1,000
Megabyte (decimal)	MB	1,000,000
Gigabyte (decimal)	GB	1,000,000,000
Terabyte (decimal)	TB	1,000,000,000,000
Kibibyte (binary)	KiB	1,024
Mebibyte (binary)	MiB	1,048,576
Gibibyte (binary)	GiB	1,073,741,824
Tebibyte (binary)	TiB	1,099,511,627,776

The SI prefixes kilo, mega, giga and tera mean powers of ten. To avoid confusion, the IEC approved separate binary names (kibi, mebi, gibi, tebi) in December 1998, and NIST documents them as the "prefixes for binary multiples".

In everyday software, though, the binary values are still often labelled KB, MB and GB:

Drive makers and Apple use decimal. Apple's support page defines 1 GB as 1 billion bytes and 1 TB as 1 trillion bytes for its devices' storage capacity.
Microsoft Windows reports disk and file sizes using binary values but labels them MB, GB and TB.

So the same drive is described in two units that happen to share a name.

Advertised vs shown in Windows

These are the results of converting the advertised decimal capacity into binary GB, which is what Windows displays as "GB":

Advertised capacity	Bytes	Shown in Windows (approx.)
64 GB	64,000,000,000	59.6 GB
128 GB	128,000,000,000	119.2 GB
256 GB	256,000,000,000	238.4 GB
500 GB	500,000,000,000	465.7 GB
1 TB	1,000,000,000,000	931.3 GB

The gap grows with each step up: about 2.3% at the kilo level (1,024 vs 1,000), about 6.9% at giga and about 9.1% at tera.

Your usable space will be a little lower still, because the file system, a recovery partition or pre-installed software take some space. On a phone, the operating system itself takes a significant share of the advertised storage.

How to check a drive's size with the converter

The Data Storage Converter uses the binary values for its KB, MB, GB, TB and PB units, the same way Windows counts. Byte (B) is a single byte. That makes it handy for seeing what Windows will show:

Type the advertised size in bytes. For a 1 TB drive, enter 1000000000000 (twelve zeros).

Set From to Byte (B).

Set the second box to Gigabyte (GB). The result is 931.32257462.

Look at the All Data Storage conversions list below for every unit at once. The TB row shows 0.9094947, which is why a "1 TB" drive is listed as 0.90 TB in some places.

Click any row in the list to copy that value.

To go the other way (how many bytes are in 2 binary GB), type 2, choose Gigabyte (GB) as From, and read the Byte row.

Bits vs bytes: internet speeds

Internet speeds are sold in bits per second (Mbps), while download sizes are shown in bytes. One byte is 8 bits, so divide by 8 first.

100 Mbps ÷ 8 = 12.5 million bytes per second, which is 12.5 MB/s in decimal megabytes.
In the binary megabytes most download managers and Windows use, that is about 11.92 MB per second.

The converter's Kilobit, Megabit and Gigabit units are decimal (1 Mbit = 1,000,000 bits = 125,000 bytes), as network speeds normally are. So if you enter 100 Megabit (Mbit) and convert to Megabyte (MB), you get 11.92092896: decimal bits on one side, binary megabytes on the other, which matches what you would see in Windows.

In real use, expect a bit less than that because of network overhead, Wi-Fi conditions and the server's own speed.

Quick examples

How long does a 2 GB file take on a 50 Mbps connection?

50 Mbps ÷ 8 = 6.25 million bytes per second. A 2 GB (decimal) file is 2,000,000,000 bytes, so 2,000,000,000 ÷ 6,250,000 = 320 seconds, a little over 5 minutes in ideal conditions.

Why does my 2,000,000,000-byte video show as 1.86 GB?

Because 2,000,000,000 ÷ 1,073,741,824 = 1.86 binary GB. The converter shows 1.86264515.

Is 1 GB of mobile data 1,000 MB or 1,024 MB?

It depends on how your operator measures it. The converter's own GB-to-MB result is 1,024 because it uses binary units throughout.

Common mistakes

Thinking the drive is faulty or fake because it shows 931 GB. That figure is expected for a genuine 1 TB drive.
Mixing bits and bytes. "Mb" or "Mbps" is megabits; "MB" is megabytes. The 8 times difference is often the cause of "slow download" confusion.
Comparing numbers from different devices. A Mac and a Windows PC can show different sizes for the same file because one uses decimal and the other binary units.
Expecting exact petabyte values from the converter. Its PB unit uses a rounded factor, so PB conversions are approximate; for PB-scale numbers, convert from bytes with your own calculation.

Related tools

For file sizes in other contexts, see why a photo under the KB limit can still be rejected, which covers the same 1,000 vs 1,024 problem on upload forms. If you are converting number systems rather than units, the Number Base Converter handles binary, decimal and hexadecimal, and the guide on converting text to binary explains how text becomes bits.