Definitions
A decimal gigabyte (GB) is 1,000,000,000 bytes; a decimal terabyte (TB) is 1,000 GB, or 1,000,000,000,000 bytes. A binary gibibyte (GiB) is 1,073,741,824 bytes; a tebibyte (TiB) is 1,024 GiB, or 1,099,511,627,776 bytes.
Conversion formulas
| Conversion | Formula | Example |
|---|---|---|
| GB to TB | GB ÷ 1,000 | 3,500 GB = 3.5 TB |
| TB to TiB | TB × 10¹² ÷ 2⁴⁰ | 10 TB ≈ 9.09 TiB |
| TiB to TB | TiB × 2⁴⁰ ÷ 10¹² | 10 TiB ≈ 11.00 TB |
Calculation example
A drive sold as 12 TB contains 12 trillion bytes. Dividing by the binary TiB size gives about 10.91 TiB before formatting, filesystem metadata, snapshots, or array protection. That smaller figure is expected; it does not mean the drive has lost capacity.
How Data Storage Lab tools use units
Capacity inputs and planning outputs use decimal TB unless the result explicitly says TiB. This matches drive labels and keeps calculations consistent between the Annual Storage Growth Calculator, Creator Media Storage Planner, Computer Backup Storage Planner, Small Office Storage Planner, and Media Library Storage Planner.
Common mistakes
- Comparing an operating-system TiB display directly with a decimal-TB drive label.
- Calling raw installed capacity the usable capacity of a protected array.
- Counting backup capacity inside the primary array’s free space.
- Rounding intermediate values before applying growth and headroom.
Limits
Unit conversion does not account for filesystem overhead, snapshot reserve, RAID or mirror overhead, sector format, compression, or deduplication. Treat it as a unit check before applying the appropriate tool’s capacity model.
Related guide
For a complete capacity-sizing method, read How Much NAS Storage Do I Need? and then use the Home Storage & Backup Planner for a complete initial configuration.