Big5 is the dominant legacy encoding for Traditional Chinese, used in Taiwan, Hong Kong, and Macau before UTF-8 became standard. It stores the thousands of Traditional Chinese characters as two-byte sequences while keeping ASCII single-byte.

How many bytes per character?

ASCII characters take one byte (0x00 to 0x7F). Each Chinese character takes two bytes: a lead byte from 0x81 to 0xFE and a trail byte from 0x40 to 0x7E or 0xA1 to 0xFE, leaving a gap in the trail range.

Why might a character be unmapped?

Big5 covers Traditional Chinese and ASCII, not Simplified-only characters, many rare ideographs, emoji, or other scripts. Those have no Big5 bytes and are flagged with ?? when encoding so nothing is silently lost.

Is Big5 the same as GBK?

No. GBK / GB2312 encodes Simplified Chinese with a different byte layout, and Big5 encodes Traditional Chinese. The same logical character generally has different bytes in each, so the encoding name must travel with the data.

Does the conversion happen locally?

Yes. The Big5 table is built in your browser from the native decoder and used locally for both encoding and decoding. No text is sent to any server.

What is the Big5 Encoder/Decoder?

Encode Traditional Chinese text to Big5 byte pairs shown as hex, or decode Big5 hex bytes back to text. Implements the single-byte ASCII range plus the two-byte lead and trail ranges, runs locally in your browser, and flags characters outside the Big5 repertoire. It runs free in your browser on Gera Tools, with nothing uploaded.

Big5 Encoder/Decoder

Name: Big5 Encoder/Decoder
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Big5 is the established legacy encoding for Traditional Chinese, long used across Taiwan, Hong Kong, and Macau. It keeps ASCII as single bytes and stores each Traditional Chinese character as a two-byte pair. This tool encodes Traditional Chinese text into Big5 hex bytes and decodes Big5 bytes back into text.

How it works

ASCII characters 0x00–0x7F are stored as one byte. Every Chinese character is two bytes: a lead byte in 0x81–0xFE followed by a trail byte in 0x40–0x7E or 0xA1–0xFE. The gap between 0x7F and 0xA0 in the trail range is what keeps Big5 distinguishable from other double-byte schemes.

To use the exact Big5 mapping, the tool enumerates the single-byte range and all valid lead/trail pairs, decodes each pair with the browser’s native Big5 decoder, and builds a character-to-bytes map. Encoding looks each input character up in that map; decoding passes the hex bytes through the native decoder.

Example and notes

"中文" encodes to a4 a4 a4 e5 — two characters, each a two-byte pair, with 中 as A4 A4 and 文 as A4 E5.
Big5 is for Traditional Chinese; Simplified-only characters and many rare ideographs are not in the table and will be flagged as unmapped.
Several Big5 extensions exist (Big5-HKSCS adds Hong Kong characters). This tool follows the encoding your browser’s standard Big5 decoder implements; for full Unicode coverage, use UTF-8.

When Big5 encoding still matters

Although UTF-8 has become the default encoding on the web, Big5 is still encountered in several practical scenarios:

Legacy Taiwanese government documents — official documents, forms, and databases produced before the mid-2000s often used Big5 exclusively, and archived systems still rely on it.
Older Windows installations set to Traditional Chinese — Microsoft’s Windows CP950 is a superset of Big5 that adds a few hundred characters; files from these systems decode with standard Big5 but may contain bytes in the CP950 extension range.
Email headers and MIME-encoded attachments — email originally designed for 7-bit ASCII sometimes carries Traditional Chinese text as charset=big5 MIME parts, and mail clients that strip the encoding declaration need a manual decode step.
Terminal emulation and BBS culture — Taiwan’s BBS community (particularly PTT) maintained Big5-encoded text art and legacy terminal sessions well into the 2010s, and archival projects still process these files.

Big5 versus GB2312/GBK

The two most common legacy Chinese encodings cover different scripts and byte layouts:

Property	Big5	GB2312 / GBK
Script	Traditional Chinese (Taiwan/HK/Macau)	Simplified Chinese (mainland China)
Lead byte	0x81 – 0xFE	0x81 – 0xFE (GBK); 0xA1 – 0xF7 (GB2312)
Trail byte	0x40–0x7E, 0xA1–0xFE	0x40–0xFE
Character count	~13,000	~21,000 (GBK)

Because the byte ranges overlap but the mappings differ completely, mistakenly reading a Big5 file as GBK (or vice versa) produces garbled text (mojibake). Always carry the encoding label with the data.