What a base means
Base 10 uses ten digits and each place is worth ten times the one to its right. Computers use base 2 (binary), and programmers often write base 16 (hexadecimal) because one hex digit equals exactly four bits. Octal (base 8) appears in Unix file permissions.
Useful related tools
Working with colours? The colour converter turns HEX into RGB. For text, try Base64, and for very large or small numbers see the scientific notation converter.
Frequently asked questions
How do I convert binary to decimal?
Multiply each digit by 2 raised to its position, counting from 0 on the right, and add the results. 1101 is 1×8 + 1×4 + 0×2 + 1×1 = 13.
Which digits can I use?
Digits 0 to 9, then letters A to Z for values 10 to 35. The base must be larger than the biggest digit you use, so base 2 only allows 0 and 1.
Can it handle huge numbers?
Yes. It uses exact whole-number arithmetic, so a 64-bit or even a 500-digit number converts without rounding.
Does it support fractions?
No, only whole numbers, which covers most programming uses. Negative numbers are fine, with a minus sign.