Convert Hex to BCD

Packed BCD stores two decimal digits per byte – each digit occupies exactly 4 bits. So decimal 25 becomes one byte 0010 0101. Unpacked BCD uses a full byte per digit, with the high nibble zeroed – decimal 25 becomes two bytes 00000010 00000101. Packed is twice as dense; unpacked is easier for mainframe zoned-decimal I/O.

COMP-3 (computational-3) is IBM’s signed packed-BCD format, standard in COBOL on z/OS mainframes. Each decimal digit is 4 bits, and the final nibble holds a sign: C (binary 1100) for positive or D (1101) for negative. Decimal 25 becomes 0010 0101 1100 (12 bits), and −25 becomes 0010 0101 1101. Used to transfer signed decimals between modern systems and mainframes.

Because 16+ digit hex values exceed JavaScript’s Number.MAX_SAFE_INTEGER (2⁵³ − 1 ≈ 9 × 10¹⁵). Using regular Number, the hex FFFFFFFFFFFFFFFF (64-bit max) would silently lose precision. BigInt handles any width exactly, so 20-digit or 40-digit hex values round-trip perfectly to BCD.

All common ones. Bare digits (FF), C-style prefix (0xFF or 0XFF), with spaces (DE AD BE EF), with underscores (DE_AD_BE_EF), and any mix. Case-insensitive – aB and Ab both work. Leading - or + sign is accepted (but non-COMP-3 formats reject negatives).

Only that line fails. The tool processes lines independently, so a stray Z in one row becomes a single red entry in the breakdown (“Line 3: invalid hex character ‘Z’ at position 2”) while every other line still converts. The stats row shows exactly how many succeeded versus failed.

Four real-world reasons. One: mainframe integration – COBOL databases still store financial amounts as COMP-3. Two: avoiding float rounding in money math – BCD represents decimal digits exactly, unlike binary floating-point. Three: 7-segment display drivers expect packed BCD. Four: some legacy industrial PLCs and calculator ASICs still emit BCD over their I/O pins.

Because neither format has a built-in way to represent sign. Packed and unpacked BCD store digit nibbles only – there’s no sign bit to set. Historical systems used accompanying sign bytes or agreed-upon conventions, but those aren’t portable. COMP-3 was invented specifically to encode sign in the same stream, so the tool restricts negative input to that mode.

For packed BCD, it’s 4 × (number of decimal digits in your value). For unpacked, 8 × decimal digits. For COMP-3, 4 × digits + 4 bits for the sign nibble, padded up to the next byte boundary. Example: decimal 12,345 → 5 digits → packed 20 bits, unpacked 40 bits, COMP-3 24 bits. The stats row shows the bit count per row.

No. All arithmetic runs in your browser’s JavaScript engine – no network requests fire during conversion, and no server stores or logs your hex values. The tool keeps working after you disconnect from the internet. You can verify with your browser’s Network tab.

Yes. Packed and unpacked BCD are bijective with their decimal values, and any decimal can be written back to hex exactly. Use a BCD-to-hex converter (or decode the BCD to decimal mentally, then convert decimal to hex) and you’ll get the original hex back. COMP-3 also round-trips losslessly, including sign.