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.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 |