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Number Base Converter
Convert between binary, octal, decimal, hex and Roman numerals.
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Number bases
Roman numerals
How base conversion works
In a positional number system with base b, each digit is multiplied by a power of the base: value = dₙ·bⁿ + … + d₁·b¹ + d₀·b⁰. For example hexadecimal FF = 15·16 + 15 = 255, and binary 1010 = 8 + 2 = 10. To go the other way, repeatedly divide by the target base and read the remainders from last to first. This tool uses arbitrary-precision integers (BigInt), so values far beyond 2⁵³ stay exact. Negative numbers are supported with a leading minus sign; prefixes such as 0x, 0b and 0o and spaces / underscores are ignored.
Roman numerals
Roman numerals combine I (1), V (5), X (10), L (50), C (100), D (500) and M (1000). A smaller symbol before a larger one is subtracted — only in the pairs IV, IX, XL, XC, CD and CM. So 2026 = MMXXVI and 1994 = MCMXCIV. Standard notation goes up to 3999 (MMMCMXCIX); invalid forms such as "IIII" or "VX" are rejected.