Go to Sublime Text > Preferences > Settings – User
Add a "rulers" setting with the lines you want for the ruler:
// Adds a single vertical ruler at column 80
"rulers": [80],
If you want multiple rulers, separate the values with a comma:
// Adds two vertical rulers: one at column 80 and one at column 120
"rulers": [80, 120],
Rulers not showing? Rulers are only shown when using a monospace font, which is the default font for Sublime Text. Ensure you are using a monospace font if the settings above don’t work for you.