How to Calculate The Actual Capacity of SSD?

Firstly, let us to figure out the definition of it.

SSD capacity is the maximum amount of data that can be stored on a solid-state drive. It is the user-addressable capacity and not includes non-volatile memory areas intended for the flash controller’s use.

Secondary, we should know the unit conversion for hard disk capacity.
1GB=1KB*1M Bytes
1M=1KB*1K Bytes
1KB=1KB*1Byte
1GB=K*K*K*1Bytes=K3*1Bytes

Third, according to the manufacturer of hard disk, 1KB should be 1000 Bytes, but the operating system supplier defines 1KB=1024Bytes. That’s to say the amount of difference between each 1GB is 10243/10003=0.93

So, the capacity we see in the operating system is the marked capacity in hard disk *0.93

Then, the actual capacity of 128GB is 128GB*0.93=119.04, around 119GB
32GB is 32GB*0.93=29.76, around 29GB
64GB is 64GB*0.93=59.52, around 59GB
256GB is 256GB *0.93=238.08, around 238GB

Do you master the methods to measure storage capacity?