BCD (Binary Coded Decimal) Converter

Convert decimal digits into 8421 BCD 4-bit representations, and translate BCD back to decimal — instantly, in your browser.

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How 8421 BCD Encoding Works

BCD encodes each decimal digit (0-9) as its own dedicated 4-bit nibble, rather than converting the whole number as one binary value. The name "8421" refers to the bit weights within each nibble, read left to right.

Because 4 bits can represent 16 values but decimal only needs 10, BCD never uses the six patterns from 1010 through 1111 — those are invalid BCD. BCD trades extra bits for digit-by-digit simplicity, which is why digital clocks and seven-segment displays often use it directly.

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