Base62 converter

Base62 writes numbers using 62 symbols: the digits 0 to 9, uppercase A to Z and lowercase a to z. Because it uses only letters and digits, Base62 strings are safe in URLs, file names and HTML IDs without any escaping. It is the classic encoding behind URL shorteners, which turn an auto-increment database ID into a short slug.

How to use it

1. Enter a non-negative integer to encode it to Base62.
2. Or enter a Base62 string to decode it back to a number.

How it works

Encoding repeatedly divides the number by 62 and maps each remainder to a character, exactly as you would convert decimal to hexadecimal but with base 62. Decoding multiplies back: each character's value times 62 to the power of its position.

Example

The number 125 is 2 × 62 + 1, so with the alphabet 0-9A-Za-z it becomes 21. A larger ID such as 1000000 becomes 4C92, only four characters. Seven Base62 characters can represent more than 3.5 trillion values.

Practical notes

• Alphabet order matters. Some libraries use 0-9a-zA-Z instead of 0-9A-Za-z. Both are valid, but they produce different strings, so use the same order everywhere.
• Sequential IDs are guessable. Encoding an auto-increment ID does not hide it. If links must not be enumerable, use random IDs such as NanoID instead.
• Large numbers. JavaScript numbers lose precision above 2^53. For bigger values, encode them as BigInt or as strings.