# What is Base 62?

**Base 62** is the algorithm used by most URL shorteners to generate custom short links. To answer how it works, the first question we need to answer is: **what are bases?**

## What is a base?

When counting up, the base is the number of numbers that you count before add another digit.

We all get taught **base 10** in school. This means that once you count past ‘9’**,** you add a ‘1’ to the left of your number, and start over again from ‘0’.

## What other bases are popular?

**Binary** (base 2) are just 1’s and 0’s, and **hexadecimal** (base 16) are both used heavily in computer science.

When a base is greater than 10, we use letters to represent the digits. So for hexadecimal, we use the digits 0-9, followed by the letters A-F. F would the number 15 (in base 10), and 10 would be the number 16.

## What is base 62?

Base 62 consists of all the **normal numbers** **0-9**, plus all the **uppercase** **letters A-Z**, and all the **lowercase letters a-z**. That’s for a total number of symbols of **10 + 26 + 26 = 62**.

This means that long numbers can be represented by a short few letters. For example, the base 10 number

**Base 10: 1213542312 => Base 62: 1K7tn6**

**URL shorteners represent links internally using Base 10, counting up from 0, but display the shortened Base 62 URL on the outside.**

That is how base 62 works!