HEX Converter

How to Use the HEX Converter

This free online HEX converter turns hexadecimal, decimal, binary and plain text into each other instantly in your browser. There is no mode to choose. Paste whatever you have — 1A3, 0x1F, FF, 48 65 6C 6C 6F or Hello — and every conversion that applies to it appears at once, each with its own copy button.

A value is read two ways at the same time, because both are useful. As a number, 1A3 is 419 in decimal, 110100011 in binary and 643 in octal, and the calculation is spelled out digit by digit. As a byte sequence, the same input is 01 A3, which is how you would see it in a hex dump. Hexadecimal output uses space-separated uppercase (e.g. "48 65 6C 6C 6F" for "Hello"), the format used by debugging, network analysis and data inspection tools, and a joined form is provided alongside it.

The input format is detected automatically, and the detected choice is shown as a highlighted chip. Because some inputs are genuinely ambiguous — 100 is a valid hexadecimal, decimal and binary number — you can override the interpretation with one click and every output updates together.

Understanding Hexadecimal Notation

Hexadecimal (base 16) is a numeral system that uses sixteen distinct symbols: the digits 0 through 9 represent values zero to nine, and the letters A through F represent values ten to fifteen. Each hex digit represents exactly four bits (a nibble), making it a convenient shorthand for binary data. Two hex digits represent one byte (8 bits), which can hold values from 00 to FF (0 to 255 in decimal). This compact representation is why hexadecimal is ubiquitous in computing -- from color codes in CSS (#FF5733) to memory addresses, MAC addresses, and raw data dumps.

Text to HEX Conversion

When converting text to hexadecimal, each character is first encoded as bytes using UTF-8 encoding, then each byte is represented as a two-digit hexadecimal number. ASCII characters like letters and digits produce one byte (two hex digits) each, while non-ASCII characters such as Japanese, Chinese, or emoji produce multiple bytes. For example, the letter "A" becomes "41", while a Japanese character like "a" becomes "E3 81 82" (three bytes in UTF-8). This conversion is useful for inspecting raw byte content, debugging encoding issues, and preparing data for protocols that require hex-encoded payloads.

Binary and HEX Interconversion

Converting between binary and hexadecimal is straightforward because each hex digit maps to exactly four binary digits. For example, hex "4F" equals binary "01001111". The tool expects space-separated groups of 8 binary digits (one byte each) for Binary to HEX conversion, and space-separated pairs of hex digits for HEX to Binary conversion. This is essential for low-level programming, hardware design, and understanding bit-level data representations. Input validation ensures that only valid characters are accepted, with clear error messages in Japanese for any invalid input.

Decimal and HEX Interconversion

HEX to Decimal converts each space-separated byte to a decimal value from 0 to 255, while Decimal to HEX converts those values back to two-digit uppercase hexadecimal.

Features

• No mode selection — every applicable conversion is shown at the same time
• Hex numbers of any length, with or without a 0x prefix (1A3, 0x1F, FFFFFFFF)
• Digit-by-digit calculation steps for hex to decimal
• Space-separated hex format for readability
• UTF-8 encoding for text conversion
• Input validation with Japanese error messages
• One-click copy to clipboard
• Client-side only -- your data stays in your browser

HEX変換ツールの使い方

この無料オンラインツールは、16進数・10進数・2進数・テキストを相互変換します。変換モードを選ぶ必要はありません。1A3・0x1F・FF・48 65 6C 6C 6F・Hello のように、手元にあるものをそのまま貼り付けると、 変換できる形式がすべて同時に表示されます。各行にコピーボタンが付いています。

入力は「数値として」と「バイト列として」の2通りで同時に解釈します。 たとえば 1A3 は、数値としては10進419・2進110100011・8進643であり、 その計算過程も桁ごとに表示します。同じ入力をバイト列として見ると 01 A3 で、 これはHEXダンプで目にする形です。

入力形式は自動判定し、判定結果をチップで表示します。100 のように16進・10進・2進のどれとしても読める入力もあるため、 解釈はワンクリックで切り替えられ、切り替えると全ての出力が一斉に更新されます。 全ての処理はブラウザ上で完結します。

16進数とは

16進数は0-9とA-Fの16個の記号を使う記数法です。2桁の16進数で1バイト(0-255)を表現でき、 バイナリデータの簡潔な表記として広く使われています。CSSの色コード(#FF5733)、 メモリアドレス、MACアドレスなど、プログラミングの様々な場面で登場します。

テキストとHEXの変換

テキストからHEXへの変換では、UTF-8エンコーディングでバイト列に変換した後、 各バイトを2桁の16進数で表現します。ASCII文字は1バイト、日本語文字は通常3バイト、 絵文字は4バイトとなります。エンコーディングの問題をデバッグする際に便利です。

Hex to Byte Converter — what the bytes mean

When you use this page as a hex to byte converter, each two-digit pair (00–FF) maps to one byte (0–255). Spaces between pairs are optional separators for readability. Converting hex to bytes is the first step when you inspect binary protocols, file headers (magic numbers like 89 50 4E 47 for PNG), or debug character encoding issues — and converting hex back to text decodes those bytes as UTF-8.

よくあるエラーと対処 / Common Errors and Fixes

言語別コード例 / Code Examples

JavaScript

// テキスト → HEX
const hex = Array.from(new TextEncoder().encode("Hello"))
  .map((b) => b.toString(16).padStart(2, "0")).join(" ");
// "48 65 6c 6c 6f"

// HEX → テキスト
const bytes = new Uint8Array("48 65 6c 6c 6f".split(" ").map((h) => parseInt(h, 16)));
const text = new TextDecoder().decode(bytes); // "Hello"

Python

"Hello".encode("utf-8").hex(" ")        # '48 65 6c 6c 6f'
bytes.fromhex("48 65 6c 6c 6f").decode() # 'Hello'

Shell (xxd)

printf 'Hello' | xxd -p     # 48656c6c6f
echo 48656c6c6f | xxd -r -p  # Hello

Go

import "encoding/hex"
h := hex.EncodeToString([]byte("Hello"))  // "48656c6c6f"
b, _ := hex.DecodeString("48656c6c6f")    // []byte("Hello")

変換例 / Before & After

テキスト → HEX:
"Hello"   → 48 65 6C 6C 6F
"こんにちは" → E3 81 93 E3 82 93 E3 81 AB E3 81 A1 E3 81 AF  (3バイト×5文字)

HEX → バイナリ:
48 65 → 01001000 01100101

ファイルヘッダの識別(マジックナンバー):
89 50 4E 47 → PNG画像 / FF D8 FF → JPEG / 50 4B → ZIP

Why browser-only?

Hex dumps often come from places you should not paste into random websites: memory dumps, packet captures, auth tokens, or proprietary file formats. This hex to byte converter runs entirely in your browser with TextEncoder/TextDecoder — the data never leaves your device, there is no upload, no logging, and it keeps working offline. Verify it yourself in the DevTools Network tab.

HEXダンプの中身はメモリダンプ・パケットキャプチャ・トークンなど機密データであることが多いもの。 本ツールは変換の全てがブラウザ内で完結し、データは一切外部送信されません。