Convert between decimal, binary, octal, hexadecimal, and Roman numerals
Enter a number to see conversions
Convert between metric and imperial units for length, weight, temperature, and more
Convert between bits, bytes, KB, MB, GB, TB, PB with binary and SI modes
Convert numbers to words in English, Vietnamese, Japanese, and Chinese
Encode and decode Base64 strings
Number System Converter is a free online tool that converts numbers between five systems: decimal (base-10), binary (base-2), octal (base-8), hexadecimal (base-16), and Roman numerals. This tool is essential for programmers, computer science students, digital electronics engineers, and anyone working with different number representations. The decimal system is what we use daily, with digits 0-9. Binary uses only 0 and 1 and is the fundamental language of computers and digital circuits. Octal uses digits 0-7 and was historically used in computing as a compact representation of binary. Hexadecimal uses digits 0-9 and letters A-F, providing a human-friendly way to represent binary data (each hex digit maps to exactly 4 binary bits). Roman numerals use letters (I, V, X, L, C, D, M) and are still used for numbering chapters, clock faces, and formal documents. Enter a number in any supported system and the tool instantly shows its representation in all other systems. Binary, octal, and hexadecimal conversions handle any non-negative integer. Roman numeral conversion supports values from 1 to 3,999. All processing happens in your browser with no data sent to any server.
Base systems: Decimal (base-10): digits 0-9 Binary (base-2): digits 0, 1 Octal (base-8): digits 0-7 Hexadecimal (base-16): digits 0-9, A-F Roman numerals: I=1, V=5, X=10, L=50, C=100, D=500, M=1000 Subtractive notation: IV=4, IX=9, XL=40, XC=90, CD=400, CM=900 Examples: 255 = 11111111 (bin) = 377 (oct) = FF (hex) = CCLV (Roman) 42 = 101010 (bin) = 52 (oct) = 2A (hex) = XLII (Roman) 1024 = 10000000000 (bin) = 2000 (oct) = 400 (hex) = MXXIV (Roman)