💾 Digital Storage Converter
Drive makers use decimal (1 TB = 1 trillion bytes). Operating systems use binary (1 TiB = 1,099,511,627,776 bytes). A terabyte drive reports as 931 gigabytes — not a lie, just two different math systems using the same abbreviation.
Last updated — conversions use exact ISO unit definitions.
How it works
Storage capacity is famously confusing because the industry uses two different prefix systems. Decimal (SI) prefixes are powers of 1,000: 1 MB = 1,000,000 bytes. Binary (IEC) prefixes are powers of 1,024: 1 MiB = 1,048,576 bytes. Hard drives advertise in decimal; operating systems report in binary — that's why a "1 TB" drive shows as about 931 GB in Windows.
The conversion factor between them is 1,024 / 1,000 = 1.024 at every step. So 1 decimal gigabyte ≈ 0.931 binary gibibyte. This tool shows both columns so you can see exactly where the number comes from.
Smaller units are unambiguous (KB, MB work fine), but once you hit GB vs GiB, TB vs TiB, and PB vs PiB, the difference compounds. That "16 GB RAM" in your laptop is actually 16 GiB (17.18 billion bytes), while your 500 GB SSD is decimal (500,000,000,000 bytes).
Why 1 TB = 931 GB
Decimal: 1 TB = 10¹² bytes. Binary: 1 TiB = 2⁴⁰ bytes. The ratio: 1 TB ÷ 1,099,511,627,776 = 0.9095 × 1024 = 931.32 GiB. The gap grows with scale: at the PB level, it's over 13%.
Why does my 1 TB drive show 931 GB?
Drive makers use decimal (1 TB = 10¹² bytes). Your OS uses binary (1 TiB = 1,099,511,627,776 bytes). The ratio is about 0.9095, so 1 TB decimal = 931.32 binary GB.
Why two prefix systems?
Decimal prefixes (kB, MB, GB) follow ISO 1000-standard. Binary (KiB, MiB, GiB) was standardized by the IEC in 1998 for base-2. Windows stubbornly uses decimal abbreviations for binary values.
Do I really need to care?
Solid-state drive shoppers: binary. Cloud storage (AWS S3, Google Drive): decimal (they round up, so you lose less). Networking: decimal (Gbps = 10⁹ bits/s).
General information only — see our disclaimer.