# Why does Windows 7 recognize a 4 GB SDHC card only with 3.68 GB? How to format/get 4 GB?

I have a Kingston SDHC card 4 GB speed class 4, but on Windows 7 it's recognized only with 3.68 GB space available.

I've already formatted the card and I get only 3.68 GB. How I can get 4 GB space available on the card?

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## migrated from stackoverflow.comMar 10 '11 at 23:34

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The reason for the discrepancy is that Kingston is labeling the card based on the base-10 value of GB, where one GB is 1000000 bytes, while Windows is reporting the card based on the base-2 value of GB (also called GiB), where one GB is 1073741824 bytes.

4 * 1000000000 / 1073741824 is equal to roughly 3.7.

The answer is that you can't get 4 GB of space available because your card physically doesn't have that much space.

Hard drive and storage manufacturers like to use 10^9 as the value for a GB because it lets them advertise more space. 2^30 is the actual relevant measurement.

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It is not just hard drive mfg's who consider the "G" unit prefix to stand for 10-to-the-9th-power: it is anyone who understands what the metric prefixes mean and have been used to signify since the nineteenth century! – kreemoweet Oct 9 '12 at 21:04

This is common. The size of the card is advertised as 4GB where 1GB is 1,000 MB. However, that is not accurate. There are actually 1,024 MB in a full GB. Manufacturers use the "1,000" all the way through the conversion instead of the correct 1,024.

Using the proper number to calculate gigabytes should give you something like 4GB = 4,294,967,296 bytes. However, the manufacturer advertises 4GB = 4,000,000,000 bytes. 4,000,000,000 bytes is, in fact, around 3.68GB.

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There is nothing wrong in considering 1 GByte = 1,000,000,000 bytes. Quite the reverse, actually. – kreemoweet Oct 9 '12 at 21:07

Binary/Decimal differences is one option, but I think in the case the "missing" space is simply reserved during formatting for file system information... it's why you can have a file with a really long name that's still shown as taking up zero space on the drive. Those file names and other metadata have to be stored somewhere.

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Reserving 10% of the capacity for file system information seems a lot to me. – Bernhard Aug 4 '12 at 13:35