Hexadecimal to Decimal Converter
Convert a hexadecimal number to decimal — or between hex, decimal, binary, and octal in any direction. Accepts an optional 0x / 0b / 0o prefix and lowercase digits, and stays exact for very large values.
About this converter
Hexadecimal is base 16: digits 0–9 then A–F for values 10–15. It is compact for binary data because one hex digit is exactly four bits. This tool parses your input in the chosen base into an exact integer and re-renders it in the target base.
All arithmetic uses BigInt, so a long hex string never loses precision the way a floating-point number would above 253.
How to use it
- Type or paste the number in the input field.
- Set "From" to the base your number is written in (Hexadecimal by default) and "To" to the base you want.
- Read the result. When the target is not decimal, the decimal value is also shown underneath.
- Press Copy result, Swap to send the result back into the input, or Clear to empty the field.
The result updates as you type — there is no Calculate button. Use Swap to reverse the two units, and Reset to return to the defaults.
How the conversion works, with examples
value = Σ digitᵢ × baseⁱ, summing from the right with i starting at 0.
| Hexadecimal | Decimal |
|---|---|
| FF | 255 |
| 10 | 16 |
| 1A | 26 |
| 100 | 256 |
| 0xDEADBEEF | 3735928559 |
FAQ
How do I convert a hexadecimal number to decimal by hand?
Multiply each digit by 16 raised to its position from the right (starting at 0) and add them up. For 1A: A is 10, so 1×16 + 10×1 = 26. FF is 15×16 + 15 = 255.
Does it accept a 0x prefix and lowercase letters?
Yes. 0xFF, 0Xff, and ff all parse to 255. Spaces and underscores between digits are ignored, so 0xFF_FF is fine.
Can it handle very large numbers?
Yes. The conversion uses JavaScript BigInt, so values far beyond 2^53 (where a normal JavaScript number would lose precision) are converted exactly. A 64-hex-digit value converts without error.
What happens if I type an invalid character?
The tool shows "Enter a valid hexadecimal number using 0–9 and A–F." and does not produce a result until the input is valid. It never returns a wrong answer for bad input.
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