Actual vs Advertised Storage
See how much usable space your drive really has after formatting.
Results
Drive manufacturers measure capacity in decimal gigabytes (1 GB = 1,000,000,000 bytes) while operating systems display binary gibibytes (1 GiB = 1,073,741,824 bytes). This mismatch plus filesystem overhead means your drive always shows less usable space than advertised. This calculator reveals the exact numbers so you know what to expect from any new drive.
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Frequently asked questions
Manufacturers count 1 TB as 1,000,000,000,000 bytes (decimal). Your OS divides by 1,073,741,824 to get GiB, yielding about 931 GiB. After filesystem overhead, you see roughly 912-920 GiB of usable space.
About 456-461 GiB depending on filesystem. The binary conversion gives 465.66 GiB, then formatting takes another 1-2%. You lose roughly 40 GB compared to the advertised capacity.
Slightly. NTFS reserves about 2% for the Master File Table and metadata. APFS and ext4 use about 1.5%. The difference between filesystems is small - most of the lost space comes from the decimal-to-binary conversion.
Yes. The decimal vs binary discrepancy applies to all storage devices - SSDs, HDDs, USB drives and SD cards. A 256GB SD card shows about 238 GiB regardless of drive technology.
Multiply the advertised capacity in TB by 1,000,000,000,000 to get bytes, then divide by 1,073,741,824 to get GiB. For a 2TB drive: 2,000,000,000,000 / 1,073,741,824 = 1,862.6 GiB. Subtract 1-2% for filesystem overhead.