Best Online Hex Converters Compared (2026)

If you are reverse-engineering a smart card APDU, decoding an EMV tag value, or debugging a binary protocol, you need a hex converter that goes beyond basic hex-to-decimal. But most online hex converters only do one or two conversions, lack endianness support, and cannot handle 64-bit values. We tested the top online hex converters so you can pick the right one.

Quick Comparison Table

1. CardWise Hex Converter — Most Complete

CardWise is the only free online hex converter designed for smart card and EMV developers. It handles the full spectrum of number base conversions while also supporting byte-level operations critical for low-level development: endianness, signed/unsigned interpretation, and ASCII/hex byte conversion.

Key advantages for developers and security engineers:

• Seven simultaneous outputs — Hex, Decimal, Binary, Octal, Hex with 0x prefix, Hex Bytes (space-separated), and Base64
• Auto-detect input format — type 0x for hex, 0b for binary, 0o for octal, or plain digits for decimal; or manually select a format
• Four bit widths — 8, 16, 32, and 64-bit, with signed/unsigned two's complement toggle
• Endianness control — Big-endian (EMV, network) or Little-endian (x86, ARM), with a one-click swap endian button
• Visual bit display — per-bit grid showing each bit as blue (1) or gray (0), grouped in 8-bit bytes
• 64-bit BigInt support — handles full 64-bit values without JavaScript number precision loss
• Five presets — EMV Amount 9F02, AID A000000004, Status Word 6A82, ASCII ‘CardWise’, Bitmask 0xFFFF0000
• Zero data upload — pure JavaScript BigInt arithmetic, no server calls

2. RapidTables Hex to Decimal — Popular Simple Tool

RapidTables offers one of the most visited online hex-to-decimal converters. Its interface is clean and straightforward: enter a hex value, get the decimal, binary, and octal equivalents.

Pros: Client-side (no data upload), real-time conversion, trusted reference site, includes a hex-to-ASCII reference table, clean UI.

Cons: Only three output formats (decimal, binary, octal), no bit width selection, no signed/unsigned, no endianness, no ASCII/hex conversion, no Base64, no visual bit display, no presets, limited 64-bit support (JavaScript number precision loss).

3. BinaryHexConverter — Multi-Format with ASCII

BinaryHexConverter provides hex to decimal, binary, octal, and ASCII conversions. It supports both text-to-hex and hex-to-text operations.

Pros: Multiple output formats including ASCII, bidirectional hex/ASCII conversion, clean interface.

Cons: Server-side processing (your data is uploaded), no real-time conversion (requires button click), no bit width selection, no signed/unsigned, no endianness, no Base64, no visual bit display, no presets, no 64-bit BigInt support.

4. GPzChris Hex Converter — Minimal Client-Side

GPzChris offers a minimal hex converter focused on hex-to-decimal and hex-to-binary conversion. It runs entirely client-side.

Pros: Client-side (no data upload), real-time conversion, minimal interface.

Cons: Only two output formats (decimal, binary), no octal, no ASCII, no Base64, no bit width selection, no endianness, no signed/unsigned, no visual bit display, no presets, limited 64-bit support.

5. HexCal.org — Simple Multi-Base

HexCal.org provides hex, decimal, binary, and octal conversion with a simple interface. It is designed for quick lookups.

Pros: Client-side, real-time conversion, includes decimal/binary/octal in one view.

Cons: No ASCII or Base64 output, no bit width selection, no endianness, no signed/unsigned, no visual bit display, no presets, limited 64-bit support, no copy buttons.

Which Hex Converter Should You Use?

Number Base Quick Reference

Understanding the four common number bases used in computing:

Frequently Asked Questions

Why does endianness matter for hex conversion?

When you convert a multi-byte hex value to a decimal number, the byte order determines the result. For example, the bytes 78 56 34 12 represent 0x12345678 (305419896) in big-endian but 0x78563412 (2018915346) in little-endian. Smart card protocols (EMV, ISO 7816, GlobalPlatform) use big-endian (network byte order). x86 and ARM processors use little-endian. If you are decoding a 4-byte EMV tag value, you need big-endian; if you are reading an x86 memory dump, you need little-endian.

Why do I need 64-bit BigInt support?

JavaScript numbers are 64-bit floating-point values, which can only represent integers up to 2^53 (about 9 quadrillion) without precision loss. Many smart card and cryptography values exceed this — for example, a 64-bit EMV application transaction counter (ATC) or a 64-bitDES key. CardWise uses JavaScript BigInt to handle the full 64-bit range (up to 2^64 - 1 = 18,446,744,073,709,551,615) without any precision loss.

What is two's complement and why do I need it?

Two’s complement is how computers represent signed (positive and negative) integers. In an 8-bit system, the byte 0xFF can represent either 255 (unsigned) or -1 (signed two’s complement). When debugging APDU status words or EMV tag values, you may need to interpret the same hex bytes as either signed or unsigned depending on the specification. CardWise lets you toggle between signed and unsigned interpretation with one click.

What is the difference between hex bytes and hex number?

Hex bytes (43 61 72 64) represent a sequence of individual byte values, typically used when inspecting raw data like APDU payloads or file contents. A hex number (0x43617264) represents a single large integer. CardWise displays both: hex bytes for data inspection and hex number for mathematical conversion. The same bytes can represent different numbers depending on endianness.