Estimates and calculations

For calculations, let’s start by asking some questions:

• What characters can we use for short URLs? Our options are as follows:
  • a-z, A-Z, 0-9. So, it’s 62 characters.
  • If you want to use more characters, -, ., _, and ~, so, there’s a total of 66 characters.
  • Let’s stick to just 62 characters.
• What’s the scale we are operating at? Let’s make some assumptions here:
  • We have 1 B users.
  • About 10% create short URLs (100 M users).
  • Each user creates 1 URL per day, so 100 M URLs per day.
  • We store these URLs for 10 years. So, 100 M * 1 * 365 * 10 = 365 B URLs.
• How many characters would we have in the short URL? Now, to have 365 B unique URLs, how many characters do we need to create unique URLs? Let’s see:
  • The number of URLs if we use 6 characters is 62^6 = 56 B URLs, but our requirement is to have 365 B URLs. So, we need to use more characters.
  • If we use 7 characters, we have 62^7 = 3.5 T.
• How much storage do...