Hex Converter — Hex / Decimal / Binary / Octal

Convert between hexadecimal, decimal, binary, and octal number systems. Supports signed/unsigned integers up to 64-bit, ASCII ↔ hex byte conversion, and visual bit display. All computation in-browser — your data never leaves your device.

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Value

Input Format

Bit Width

Signedness

Endianness (for hex bytes)

📊 Conversions

Hex —

Decimal —

Binary —

Octal —

Hex (0x) —

Hex Bytes —

Base64 —

Bit View

How Hexadecimal Works

Hexadecimal (base-16) is the lingua franca of low-level computing and smart card engineering. Each hex digit represents exactly 4 bits (a nibble), so one byte is always two hex digits. This makes it trivial to read binary data: 0xFF = 255 = 11111111 in binary.

Why hex, not decimal? Decimal digits don't align to byte boundaries. The value 200 in decimal is 0xC8 in hex — instantly readable as one byte. In smart card APDUs, EMV TLV data, and cryptographic keys, every value is expressed in hex because each pair of digits maps perfectly to one byte on the wire.

Number Base Reference

Base	Name	Digits Used	Prefix	Example (decimal 255)
2	Binary	0, 1	0b	0b11111111
8	Octal	0–7	0o / 0	0377
10	Decimal	0–9	(none)	255
16	Hexadecimal	0–9, A–F	0x	0xFF

Smart Card Use Cases

Scenario	Example	Notes
EMV Tag 9F02 Authorized Amount	000000011934 → $119.34	12-digit BCD, n6 padded. Two digits per byte, last 2 = cents
APDU status word SW1 SW2	0x9000 (success), 0x6A82 (file not found)	Always 2 bytes, big-endian
AID (Application Identifier)	A0000000041010 (Mastercard)	5-16 bytes, RID + PIX, big-endian
ATR historical bytes	3B ... 8031E073FE21123456782900	Variable length, protocol info
Cryptographic key (3DES)	0123456789ABCDEFFEDCBA9876543210	16 bytes = 32 hex chars (double-length DES key)
Bit masks / flags	0xFF00 = high byte set, low byte clear	Common in access bits, capability flags

EMV Amount Encoding (BCD)

EMV Tag 9F02 (Amount, Authorized) is stored as a 6-byte BCD (Binary-Coded Decimal) value. Each nibble represents one decimal digit. For example, $119.34 is encoded as 00 00 00 01 19 34 — 6 bytes, 12 nibbles, where the last 2 digits are the decimal portion (cents).

Try it: Click "EMV Amount 9F02" above, then look at "Hex Bytes" to see the 6-byte BCD encoding. The decimal value 11934 represents $119.34.

Signed vs Unsigned (Two's Complement)

When interpreting a hex value as a signed integer, the most significant bit (MSB) determines the sign. If the MSB is 1, the value is negative and computed via two's complement:

Examples (8-bit):
  0x7F = 0111 1111 = +127  (max positive)
  0x80 = 1000 0000 = -128  (min negative)
  0xFF = 1111 1111 = -1
  0x00 = 0000 0000 = 0

For n-bit two's complement:
  if MSB == 1:  value = -(2^n - unsigned_value)

Endianness

Multi-byte integers can be stored big-endian (most significant byte first) or little-endian (least significant byte first). Smart card protocols (EMV, ISO 7816, GlobalPlatform) almost universally use big-endian. x86 CPUs and many ARM implementations use little-endian.

Value	Big-endian (EMV/network)	Little-endian (x86)
0x1234ABCD	12 34 AB CD	CD AB 34 12
0x0000FFFF	00 00 FF FF	FF FF 00 00

Use the "Swap Endian" button to reverse byte order — useful when converting between smart card data (big-endian) and x86 memory dumps (little-endian).

Related Tools

EMV Tag Lookup — Search EMVCo tags by hex value (9F02, 5A, 57, ...)
EMV TLV Parser — Parse BER-TLV TLV data containing hex-encoded EMV tags
APDU Command Builder — Build APDUs with hex command data
CRC Calculator — Compute CRC checksums on hex input
Base64 Encoder / Decoder — Convert hex bytes to/from Base64
BER-TLV Parser — Parse raw hex BER-TLV structures