USB - Why does my USB drive show less capacity than stated on my PC or MAC

The difference is due to way that most storage manufacturers and PC manufacturers define a scale. There are two systems decimal and binary.

Storage devices use a decimal system and PCs use the binary system -this leads to some discrepancy between actual capacity and reported capacity by a PC. The difference can be between about 2% - 9% depending on the capacity of the drive. 

Some additional capacity is taken up by features required by the operating system e.g. FAT tables and the flash drive controller e.g. spare blocks for wear levelling.

 

 

Decimal (Dec) bytes

Binary (Bin) bytes

Ratio (Dec/Bin)

% Diff

Kilobyte

103

                              1,000

210

                                      1,024

0.9765625

2%

Megabyte

106

                      1,000,000

220

                               1,048,576

0.953674316

5%

Gigabyte

109

              1,000,000,000

230

                      1,073,741,824

0.931322575

7%

Terabyte

1012

1,000,000,000,000

240

              1,099,511,627,776

0.909494702

9%

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