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Available Capacity of Drive is Smaller than Drive Label

Determining drive capacity can be confusing at times because of the different measurement standards that are often used. When dealing with Windows and macOS, both decimal measurements and binary measurements of a drive's capacity will be seen. In either case, a drive's capacity is measured by using the total number of bytes available on the drive. As long as the drive displays the correct number of bytes (approximate), the drive's full capacity is available.

Decimal vs. Binary:

For simplicity and consistency, hard drive manufacturers define a megabyte as 1,000,000 bytes, a gigabyte as 1,000,000,000 bytes and a terabyte as 1,000,000,000,000 bytes. This is a decimal (base 10) measurement and is the industry standard. However, certain system BIOSs, FDISK and Windows define a megabyte as 1,048,576 bytes, a gigabyte as 1,073,741,824 bytes and a terabyte as 1,099,511,627,776 bytes. Older macOS systems also use these values. These are binary (base 2) measurements.

To Determine Decimal Capacity:

A decimal capacity is determined by dividing the total number of bytes, by the number of bytes per gigabyte (1,000,000,000 using base 10).


To Determine Binary Capacity:

A binary capacity is determined by dividing the total number of bytes, by the number of bytes per gigabyte (1,073,741,824 using base 2). This is why different utilities will report different capacities for the same drive. The number of bytes is the same, but a different number of bytes is used to make a megabyte, a gigabyte and a terabyte. This is similar to the difference between 0 degrees Celsius and 32 degrees Fahrenheit. It is the same temperature, but will be reported differently depending on the scale being used.

Various Drive Sizes and their Binary and Decimal Capacities

Drive Size Approximate Total Bytes Decimal Capacity
(bytes/1,000,000,000)
(Usual Displayed Capacity On macOS)
Approximate Binary Capacity (bytes/1,073,724,841)
(Usual Displayed Capacity On Windows and Linux)
10 GB 10,000,000,000 10 GB 9.31 GB
20 GB 20,000,000,000 20 GB 18.63 GB
30 GB 30,000,000,000 30 GB 27.94 GB
36 GB 36,000,000,000 36 GB 33.53 GB
40 GB 40,000,000,000 40 GB 37.25 GB
60 GB 60,000,000,000 60 GB 55.88 GB
74 GB 74,000,000,000 74 GB 68.91 GB
80 GB 80,000,000,000 80 GB 74.51 GB
100 GB 100,000,000,000 100 GB 93.13 GB
120 GB 120,000,000,000 120 GB 111.76 GB
150 GB 150,000,000,000 150 GB 139.69 GB
160 GB 160,000,000,000 160 GB 149.01 GB
180 GB 180,000,000,000 180 GB 167.64 GB
200 GB 200,000,000,000 200 GB 186.26 GB
250 GB 250,000,000,000 250 GB 232.83 GB
300 GB 300,000,000,000 300 GB 279.40 GB
320 GB 320,000,000,000 320 GB 298.02 GB
400 GB 400,000,000,000 400 GB 372.52 GB
500 GB 500,000,000,000 500 GB 465.65 GB
640 GB 640,000,000,000 640 GB 595.84 GB
750 GB 750,000,000,000 750 GB 698.47 GB
1 TB (1000 GB) 1,000,000,000,000 1 TB (1000 GB) 931.30 GB
1.5 TB (1500 GB) 1,500,000,000,000 1.5 TB (1500 GB) 1396.95 GB
2 TB (2000 GB) 2,000,000,000,000 2 TB (2000 GB) 1862.6 GB
3 TB (3000 GB) 3,000,000,000,000 3 TB (3000 GB) 2793.97 GB
4 TB (4000 GB) 4,000,000,000,000 4 TB (4000 GB) 3725.29 GB
5 TB (5000 GB) 5,000,000,000,000 5 TB (5000 GB) 4657.49 GB
6 TB (6000 GB) 6,000,000,000,000 6 TB (6000 GB) 5587.94 GB
7 TB (7000 GB) 7,000,000,000,000 7 TB (7000 GB) 6519.36 GB
8 TB (8000 GB) 8,000,000,000,000 8 TB (8000 GB) 7450.58 GB
10 TB (10000 GB) 10,000,000,000,000 10 TB (10000 GB) 9613.37 GB
12 TB (12000 GB) 12,000,000,000,000 12 TB (12000 GB) 11176.04 GB
14 TB (14000 GB) 14,000,000,000,000 14 TB (14000 GB) 13038.72 GB
16 TB (16000 GB) 16,000,000,000,000 16 TB (16000 GB) 14901.39 GB
18 TB (18000 GB) 18,000,000,000,000 18 TB (18000 GB) 16763.81 GB
20 TB (20000 GB) 20,000,000,000,000 20 TB (20000 GB) 18626.74 GB
24 TB (24000 GB) 24,000,000,000,000 24 TB (24000 GB) 22352.09 GB
28 TB (28000 GB) 28,000,000,000,000 28 TB (28000 GB) 26077.44 GB
32 TB (32000 GB) 32,000,000,000,000 32 TB (32000 GB) 29802.79 GB
40 TB (40000 GB) 40,000,000,000,000 40 TB (40000 GB) 37253.49 GB
50 TB (50000 GB) 50,000,000,000,000 50 TB (50000 GB) 46566.86 GB
75 TB (75000 GB) 75,000,000,000,000 75 TB (75000 GB) 69850.29 GB
100 TB (100000 GB) 100,000,000,000,000 100 TB (100000 GB) 93133.73 GB

Details
Answer ID 16656
Published 08/20/2018 02:22 AM
Updated 01/04/2023 08:31 AM

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