Hex to decimal converter

Hexadecimal is base 16. Its digits run from 0 to F, and each place is worth 16 times the place to its right: 1, 16, 256, 4,096, 65,536 and so on.

Worked example, 0x1A3F:

1 × 16³ = 1 × 4096 = 4096
A × 16² = 10 × 256 = 2560
3 × 16¹ = 3 × 16   =   48
F × 16⁰ = 15 × 1   =   15
                     ------
                       6719

Upper and lower case mean the same thing: ff, FF and 0xFf are all 255. Hex fractions work the same way with negative powers: 0x0.8 is 8/16 = 0.5.

Whether FFFFFFFF is 4,294,967,295 or -1 depends on the type that holds it, not on the bits. Pick a width in the converter’s bits panel to see both readings.

In a signed integer type the highest bit is the sign bit (two’s complement). For a hex value of a known width, if the first digit is 8 or higher the number is negative, and its value is the unsigned value minus 2 to the power of the width. FFFFFF85 as a 32-bit signed int is 4,294,967,173 - 4,294,967,296 = -123.

// JavaScript: read 32-bit hex as signed
BigInt.asIntN(32, 0xFFFFFF85n)   // -123n
0xFFFFFF85 | 0                    // -123 (bitwise ops use 32-bit ints)

# Python
v = int('FFFFFF85', 16)
v - (1 << 32) if v >= 1 << 31 else v   # -123

// JavaScript
parseInt('7DE', 16)              // 2014
Number('0x7DE')                  // 2014 (needs the 0x prefix)
BigInt('0x' + 'FFFFFFFFFFFFFFFF') // 18446744073709551615n, exact

# Python
int('7DE', 16)        # 2014
int('0x7de', 0)       # 2014, base from the prefix

// Go
n, err := strconv.ParseInt("7DE", 16, 64)    // 2014
u, err := strconv.ParseUint("FFFFFFFFFFFFFFFF", 16, 64)

# Bash
echo $((16#7DE))                # 2014
echo "ibase=16; 7DE" | bc       # 2014 (bc needs uppercase hex)

JavaScript numbers are exact only up to 2^53 - 1, which is 1FFFFFFFFFFFFF in hex (14 digits). Beyond that, parseInt rounds; BigInt does not. This converter uses BigInt, so 64-bit hashes and IDs convert exactly.

Find the first hex digit on the left and the second along the top. 0xA5 is row A, column 5: 165. For the same values in binary see the decimal to binary table; for colors written in hex, the hex to RGB converter.