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Flash Memory Actual Capacity Estimates

J515OP

Super Moderator
Here is a handy chart I Googled from a flash memory manufacturer for anybody who wants a reference. Keep this in mind when you see articles proclaiming how much space is taken by apps or OSes or by manufacturers claiming the capacity of their devices.

Capacity Estimate

1 GB USB Flash drive has 961 MB (0.94 GB) usable capacity.
2 GB USB Flash drive has 1908 MB (1.86 GB) usable capacity.
4 GB USB Flash drive has 4080 MB (3.79 GB) usable capacity.
8 GB USB Flash drive has 8067 MB (7.51 GB) usable capacity.
16 GB USB Flash drive has 16,109 MB (15 GB) usable capacity.
32 GB USB Flash drive has 31,919 MB (29.7 GB) usable capacity.
64 GB USB Flash drive has 60,949 MB (59.53 GB) usable capacity.
Source: USB Storage | Idol Memory

The manufacturer did not specify the method used to calculate usable capacity but here are the numbers according to standard calculations.

First a key to the numbers.

Decimal (used my manufacturers):
1 G = 10^9 = 1,000,000,000
1 M = 10^6 = 1,000,000
1 K = 10^3 = 1,000

These are the correct prefixes under the SI standards.

Binary (used by the OS for bytes):
1 GiB = 2^30 bytes = 1,073,741,824 bytes
1 MiB = 2^20 bytes = 1,048,576 bytes
1 KiB = 2^10 bytes = 1,024 bytes

These are the correct units for binary though by convention we drop the "i" and use the SI names which leads to the confusion.

The formula to figure actual capacity in GiB is: GB listed * 10^9 / 2^30 = calculated capacity

Calculated capacity - overheard = usable capacity

Note: overhead is inaccessible space on a formatted drive and will very slightly but can be as much as 100 MB

128 GB * 10^9 / 2^30 bytes = ~119.21 GiB
256 GB * 10^9 / 2^30 bytes = ~234.42 GiB

Summary

Using the manufacturer's numbers and the calculated numbers gives us:

1 GB : 0.94 GB stated usable capacity : ~0.93 GiB calculated capacity
2 GB : 1.86 GB stated usable capacity : ~1.86 GiB calculated capacity
4 GB : 3.79 GB stated usable capacity : ~3.73 GiB calculated capacity
8 GB : 7.51 GB stated usable capacity : ~7.45 GiB calculated capacity
16 GB : 15 GB stated usable capacity : ~14.9 GiB calculated capacity
32 GB : 29.7 GB stated usable capacity : ~29.8 GiB calculated capacity
64 GB : 59.53 GB stated usable capacity : ~59.60 GiB calculated capacity
128 GB : no stated usable capacity : ~119.21 GiB calculated capacity
256 GB : no stated usable capacity : ~234.42 GiB calculated capacity
 
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