You enter a value and select its unit. The tool first converts your input to bytes using the decimal (SI) multiplier, then divides by every unit's factor to show equivalents in both decimal and binary systems side by side. No rounding is applied until display — the underlying arithmetic uses full floating-point precision.
Drive manufacturers use decimal units (1 GB = 1,000,000,000 bytes), while your OS typically reports in binary units (1 GiB = 1,073,741,824 bytes). The drive has exactly as many bytes as advertised — the number just looks smaller in binary units.
KB (kilobyte) is 1,000 bytes in the SI/decimal system. KiB (kibibyte) is 1,024 bytes in the IEC/binary system. The IEC prefixes (KiB, MiB, GiB) were introduced in 1998 to eliminate this ambiguity.
Since macOS 10.6 (Snow Leopard), Apple uses decimal units — 1 GB = 1,000,000,000 bytes. This means the reported capacity matches the drive label. Windows still uses binary units with decimal labels, which causes the apparent discrepancy.
Formatting typically uses 1–5% of the raw capacity for the filesystem structure (allocation tables, journals, etc.). So a 1 TB drive may show around 930 GiB after both the binary conversion and formatting overhead.
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.