Binary-Coded Decimal (BCD) represents each decimal digit independently as a fixed 4-bit binary pattern. For example, decimal 25 becomes 0010 0101 in 8421 BCD, not the straight binary of 25.

The most common BCD format, where each bit in the 4-bit group carries the weight 8, 4, 2, or 1. Digits 0–9 are encoded as 0000–1001; patterns 1010–1111 are invalid.

What is Excess-3 (XS-3) BCD?

Excess-3 encodes each decimal digit by adding 3 before converting to 4-bit binary. Digit 0 becomes 0011, digit 9 becomes 1100. It is self-complementing, which simplifies BCD subtraction circuits.

How do I enter a BCD string?

Type the 4-bit groups separated by spaces (e.g., "0010 0101") or run them together (e.g., "00100101"). The tool splits them into groups of 4 from the right.

What is the maximum decimal input?

This tool supports integers with up to 15 digits (the JavaScript safe-integer limit). For longer numbers, split them into smaller parts.

BCD Converter

Name: BCD Converter
Availability: InStock
Author: Nham Vu

Convert decimal numbers to BCD (8421 or Excess-3) and back, with a live digit-by-digit breakdown.

Encoding

8421 (Standard BCD) Excess-3 (XS-3)

Decimal → BCD

BCD → Decimal

Result

Enter a value above and click Convert.

Digit Breakdown

No conversion yet.

Digit	Decimal Value	4-bit Group

Quick Reference

Dec	8421	XS-3

Summary