How much usable space is on a 1TB SSD?

Many users feel frustrated when they unbox a brand new 1TB SSD only to find they have much less usable space. Why does this happen?

On a 1TB SSD, the usable capacity shows up as about 930GB in Windows. This is a result of manufacturers using This is a result of manufacturers using decimal measurements (1TB = 1,000GB), while computers use binary measurements¹⁷ (1TB = 1,024GB), so you lose about 70GB due to this difference and further reduction by formatting, reserved space

So, why is this happening and what can you do about it? Let’s break down the exact reasons behind this capacity difference.

How much usable space is on 1TB SSD?

Most people expect to get 1,000GB from a 1TB SSD, but Windows and most operating systems only show around 930GB available. Is this normal?

A 1TB SSD usually shows roughly 930GB usable space in Windows or other operating systems. This is due to differences in how SSD manufacturers measure storage (decimal) compared to how computers report space (binary). Formatting, system files, and reserved space further reduce availability[1][3][5].

Let’s dive deeper into the numbers. When SSD manufacturers sell you a "1TB" drive, they calculate 1TB as 1,000,000,000,000 bytes (decimal). However, your computer calculates storage space in binary, where 1TB is 1,099,511,627,776 bytes (2^40). When your SSD is formatted and plugged in, your computer divides the available bytes by 1,073,741,824 (the number of bytes in a "gigabyte" using binary), resulting in about 931GB displayed. You lose about 70GB just by how numbers are counted. After this, the file system reserves a little space for metadata, and manufacturers sometimes hold back a chunk forAfter this, the file system reserves a little space for metadata, and manufacturers sometimes hold back a chunk for over-provisioning, which keeps your SSD healthy and gives you consistent performance¹⁷ long-term by balancing wear on the storage cells

Manufacturers use decimal: 1TB = 1,000GB. Computers, though, use binary: 1TB = 1,024GB. This leads to a capacity mismatch when drives are reported by your operating system[1][2][3][5].

The confusion started because, early on, operating systems like MS-DOS reported sizes in binary, while hardware makers preferred decimal for marketing simplicity. So "1 kilobyte" could be either 1,000 bytes (decimal) or 1,024 bytes (binary). This difference stacks up as you get to gigabytes andThis difference stacks up as you get to gigabytes¹⁷ and terabytes

For instance:

• Decimal: 1TB = 1,000,000,000,000 bytes (how drives are sold)
• Binary: 1TB = 1,099,511,627,776 bytes (how computers calculate)

Operating systems like Windows report the drive size using binary GB, so it looks smaller. macOS, however, sometimes reports it in decimal, showing "full" capacity as expected. The upshot: there’s about a 7% "loss" between the advertised capacity and what you see in Windows. This isn’t a trick—just a difference in calculation.

Table:

For buyers, plan on about 930GB per 1TB you purchase.

Why is my 1TB only 930?

You expected 1TB, but after formatting, you see just 930GB. Is space missing or is this completely normal?

A 1TB SSD typically displays 930GB in Windows due to decimal vs binary measuring, plus file system, over-provisioning, and recovery partitions reducing A 1TB SSD¹⁷ typically displays 930GB in Windows due to decimal vs binary measuring, plus file system, over-provisioning, and recovery partitions reducing usable capacity

Let’s look closer. After the measuring difference (about 70GB lost from decimal to binary), formatting the disk takes up a tiny amount for the file system structure and metadata. SSDs also set aside space for over-provisioning (usually 7–10%). Over-provisioning helps maintain SSD speed and lifetime by managing wear, failures, and balancing data across all storage cells[4]. If your SSD is used for your OS, Windows may automatically create hidden recovery partitions several hundred MB in size[4]. All these little chunks further slim down your usable space.

Here’s a table illustrating what happens:

For most users, 930GB is the expected, normal available space for a 1TB SSD. Always factor in these real-world numbers when planning storage for important projects.

Conclusion

A 1TB SSD typically gives about 930GB usable space due to differences in binary and decimal calculations, plus formatting and reserved areas.