Hex to Decimal Converter: Exact, Any Length

1. Type or paste the hexadecimal number. Upper and lower case digits both work, a 0x prefix is accepted, and spaces or underscores between digits are ignored, so 0xFF_FF, ff ff and FFFF are the same value.
2. Read the decimal value at the top.
3. If the hex is a signed integer, such as FFFFFFFF read from a 32-bit register, look at the Two's complement row, or switch From to two's complement and paste the bits, to see the signed value.

Each hex digit is worth sixteen times the digit to its right. The digits a to f stand for 10 to 15. Reading from the right, the places are worth 1, 16, 256, 4,096, 65,536 and so on. For 2F3: 2 × 256 + 15 × 16 + 3 = 512 + 240 + 3 = 755.

One hex digit is exactly four bits, so a byte is always two hex digits and a 32-bit word is eight. That makes hex a compact way to write memory addresses, colour values such as #FF8800, Unicode code points and hash digests. Converting to decimal is useful when a value has to be compared with a size, a count or a limit written in ordinary numbers.

Calculators and spreadsheets store numbers as 64-bit floating point, which only holds 15 to 17 significant decimal digits. A 64-bit hex value such as FFFFFFFFFFFFFFFF is 18,446,744,073,709,551,615, and a spreadsheet would round it. This page uses arbitrary-precision integers, so every digit is exact, for inputs of up to 10,000 hex digits.