Convert Octal to BCD

Regular binary represents the entire number as a single base-2 value. Decimal 25 in binary is 11001 (5 bits). BCD encodes each decimal digit separately in 4 bits. Decimal 25 in BCD is 0010 0101 (8 bits – “2” then “5”). BCD wastes bits (the codes 1010-1111 are unused in standard 8421) but lets decimal-display hardware drive each digit directly without converting back from binary.

Different historical use cases. 8-4-2-1 (also called 8421 or Natural BCD) is the standard and most common – the 4 bits weight 8, 4, 2, 1. Excess-3 (XS-3, also Stibitz code) adds 3 to each digit’s BCD value, which makes addition self-complementing and was used in early IBM machines. Aiken 2-4-2-1 uses unusual weights and is also self-complementing – once popular in early Soviet computing.

Unpacked stores one decimal digit per nibble (4 bits), often shown space-separated as in this tool’s default. Packed BCD puts two decimal digits in a single byte (one per nibble within the byte). 16-bit value 1234 in unpacked: 0001 0010 0011 0100 (16 bits = 4 nibbles, each a digit). In packed: same bits but no internal spaces and stored as 2 bytes (00010010 + 00110100) – half the storage. Most legacy systems used packed for storage and unpacked for arithmetic.

Because standard BCD uses the same 4-bit codes for digits 0-9 as hex does. Hex 0 = 0000 = BCD 0; hex 9 = 1001 = BCD 9. The difference is that hex continues with A-F (codes 1010-1111) while BCD treats those as invalid. So writing decimal 107 in hex (0x107) is character-for-character identical to writing it in 8421 BCD nibbles – handy for verification.

Mathematically: convert input to decimal first, then encode each decimal digit. Octal 153 = decimal 107 = BCD 0001 0000 0111. Hardware implementations often use the “double-dabble” algorithm to do the conversion without an intermediate decimal – but the result is the same. This tool does the BigInt-decimal step explicitly so the intermediate value is visible in the table.

Real-time clock chips (DS1307, DS3231 store time as BCD in registers), legacy financial systems where decimal precision matters more than speed (mainframe COBOL still uses packed decimal), some embedded LCD/LED display drivers, and educational digital-logic courses. Most modern computing has moved to pure binary for efficiency.

That specific line errors out (with the message “Invalid octal digit”) and gets listed in the Errors box, but other lines in your input still convert successfully. So you can paste a mixed list of values and the tool shows you exactly which ones failed.

Unlimited (BigInt). A 100-digit octal number gets converted to its ~83-digit decimal equivalent, then each decimal digit gets its own BCD nibble. Display-wise the BCD column gets very long; the table cell scrolls horizontally. For practical use under 30 octal digits is sensible.

No. All BigInt arithmetic, variant table lookup, and packing happens in your browser. Open DevTools → Network and confirm zero requests fire after the page loads. Safe for proprietary hardware register dumps or cryptographic seed materials in BCD form.

Yes. Total bundle is under 20 KB. Once loaded, disconnect and keep converting. Useful for embedded-system work or COBOL maintenance where BCD comes up constantly.