What is BCD (binary coded decimal)?

BCD stores each decimal digit in its own 4-bit group rather than converting the whole number to binary. The 8421 weighting means the four bits carry the values 8, 4, 2 and 1, so the digit 7 is 0111 (4 + 2 + 1) and 9 is 1001 (8 + 1). A four-digit number like 2026 becomes four nibbles, 0010 0000 0010 0110. Only 0000 through 1001 are used, so six of the sixteen possible nibbles are illegal.

What is the BCD of 1995?

Split 1995 into its digits 1, 9, 9, 5 and encode each as 4 bits in 8421 code. 1 is 0001, 9 is 1001, 9 is 1001 and 5 is 0101, so the packed BCD is 0001100110010101 and the grouped form is 0001 1001 1001 0101. Read straight as hex it shows 1995, which is why register dumps of packed BCD look like the decimal value.

How is BCD different from plain binary?

Plain binary converts the whole number at once, so 1995 is 11111001011, just 11 bits. BCD encodes digit by digit, so the same 1995 needs 16 bits (four nibbles). BCD wastes space because each nibble can only reach 9, never 15, but it keeps base ten exact and trivially printable. Plain binary packs tighter but a value like 0.1 cannot be stored without rounding.

Why would anyone use BCD instead of binary?

Three classic reasons. Seven segment displays and digital clocks drive one digit at a time, so a BCD nibble maps straight to a display digit with no division. Real time clock chips store hours, minutes and seconds in packed BCD. And older financial and calculator code uses BCD so cents stay exact, since amounts like 0.10 never suffer binary floating point drift.

Why does an input like 1010 fail?

1010 is binary 10, which is larger than 9, so it cannot represent a single decimal digit in 8421 BCD. The six nibbles 1010, 1011, 1100, 1101, 1110 and 1111 are all illegal in standard BCD, and this converter reports an error on any of them rather than silently inventing a value. If you meant plain binary, decode it with a base converter instead.

Drive a seven segment display from a microcontroller

You are pushing digits to a multiplexed LED display and the decoder chip wants one BCD nibble per digit. Type the number you want shown, read the grouped BCD, and copy each nibble into your lookup table or straight onto the data lines. The per-digit table makes it obvious which four bits belong to the tens versus the units, so you wire the display once and get it right.

Decode a real time clock register dump

An RTC chip reports hours, minutes and seconds in packed BCD, so a register reading of 0010 0011 looks wrong until you realise it is 23, not 35. Switch to BCD to decimal, paste the nibbles, and the tool tells you the actual time. When a value comes back as illegal it flags the bad nibble, which usually means you read the wrong register or the chip is in 12-hour mode.

Verify exact decimal handling in financial code

You are reviewing a routine that stores cents in packed BCD to dodge binary floating point drift. Encode a few amounts here, confirm the nibbles match what the code emits, and you have a quick oracle for unit tests. Because BCD never rounds, the encoded 10 cents is always 0001 0000, with no surprise representation error to chase.

Teach number representation in a digital logic class

Comparing plain binary against BCD is the moment students see why encodings are a design choice, not a law. Show 1995 as 11 bits of binary next to 16 bits of BCD, point at the six illegal nibbles, and let them try 1010 to watch it fail. The colour-keyed per-digit table turns the abstract rule into something they can read at a glance.

BCD Converter — Decimal to Binary Coded Decimal (8421)

Decimal ⇄ binary coded decimal in 8421 code, with packed view, hex and per-digit nibbles, all in your browser

Runs locally
Category Developer & DevOps
Best for Formatting, validating, shrinking, or inspecting code-adjacent text.

Direction

Input (a non-negative integer, e.g. 1995)

Group nibbles with spaces

BCD (grouped)

0001 1001 1001 0101

BCD (packed)

0001100110010101

Hex (packed)

1995

Decimal value

1995

Per-digit breakdown

Digit

Nibble

0001

1001

0101

Each decimal digit maps to one 4-bit nibble (8-4-2-1 weighting). BCD keeps decimal exact for displays and money, while plain binary packs tighter but loses base-10 cleanliness. Everything runs in your browser tab.

What this tool does

Free BCD converter for binary coded decimal in the 8421 weighting. Type a decimal number and every digit turns into its own 4-bit group, so 1995 becomes 0001 1001 1001 0101. Paste BCD bits the other way and the tool reads each nibble back to a digit, rejecting illegal groups (1010 through 1111) instead of guessing. You get the grouped view, a packed view with no spaces, the packed hex form (which reads like the decimal digits), and a colour-keyed per-digit table that lines each digit up with its nibble. Optional space grouping makes long strings legible. BCD is how seven segment displays, real time clocks and a lot of financial code keep base ten exact, since it never inherits binary rounding. Everything runs in your browser, with one-click copy and a shareable link.

Tool details

Input: Numbers; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: Shareable URL state; Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget: Initial JS <= 9 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Developer & DevOps · Developer; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

How BCD Converter fits into your work

Use it in the small gaps between coding, reviewing, debugging, and shipping.

Developer jobs

Formatting, validating, shrinking, or inspecting code-adjacent text.
Preparing snippets for documentation, tickets, commits, or handoff.
Checking a small payload quickly without switching tools.

Developer checks

Run irreversible transforms like minify or obfuscate on a copy.
Keep secrets out of pasted snippets unless the tool explicitly stays local.
Use your normal tests or linter before shipping transformed code.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Drive a seven segment display from a microcontroller
You are pushing digits to a multiplexed LED display and the decoder chip wants one BCD nibble per digit. Type the number you want shown, read the grouped BCD, and copy each nibble into your lookup table or straight onto the data lines. The per-digit table makes it obvious which four bits belong to the tens versus the units, so you wire the display once and get it right.
Decode a real time clock register dump
An RTC chip reports hours, minutes and seconds in packed BCD, so a register reading of 0010 0011 looks wrong until you realise it is 23, not 35. Switch to BCD to decimal, paste the nibbles, and the tool tells you the actual time. When a value comes back as illegal it flags the bad nibble, which usually means you read the wrong register or the chip is in 12-hour mode.
Verify exact decimal handling in financial code
You are reviewing a routine that stores cents in packed BCD to dodge binary floating point drift. Encode a few amounts here, confirm the nibbles match what the code emits, and you have a quick oracle for unit tests. Because BCD never rounds, the encoded 10 cents is always 0001 0000, with no surprise representation error to chase.
Teach number representation in a digital logic class
Comparing plain binary against BCD is the moment students see why encodings are a design choice, not a law. Show 1995 as 11 bits of binary next to 16 bits of BCD, point at the six illegal nibbles, and let them try 1010 to watch it fail. The colour-keyed per-digit table turns the abstract rule into something they can read at a glance.

Common pitfalls

Treating a BCD string as plain binary. 0001100110010101 is 1995 in BCD but a very different value if you parse it as one binary number. Pick the right direction and feed nibbles, not a raw binary integer.
Forgetting that BCD lengths must be a multiple of four. A stray digit, like 00011, has no clean nibble boundary, so the tool rejects it. Pad groups to four bits each before decoding.
Assuming all sixteen 4-bit patterns are legal. They are not. 1010 through 1111 never appear in valid 8421 BCD, so seeing one means the data is corrupt, mis-aligned, or actually plain binary rather than BCD.

Privacy

Every conversion, encoding, decoding, the hex view and the per-digit breakdown, is plain JavaScript that runs in your browser tab. No number you type ever leaves the page and nothing is logged. The one caveat is the shareable link, which encodes your input in the query string, so a link pasted into chat records that value in the recipient server's access log. For anything sensitive, use the copy button rather than the share URL.

FAQ

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BCD Converter — Decimal to Binary Coded Decimal (8421)

Per-digit breakdown

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How BCD Converter fits into your work

Developer jobs

Developer checks

Good next steps

Real-world use cases

Drive a seven segment display from a microcontroller

Decode a real time clock register dump

Verify exact decimal handling in financial code

Teach number representation in a digital logic class

Common pitfalls

Privacy

FAQ

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