Unicode Hex Input keyboard layout

You can add the Unicode Hex Input keyboard layout in System Settings > Input Sources.

The hex code for theta (θ) is U+03B8. So, to write theta, type 03B8 while holding the ⌥ Option key.

Unicode Hex Input keyboard layout

Basically, the Unicode Hex Input keyboard layout allows you to enter any character by typing its hex code while holding the ⌥ Option key.

It can be added in System Settings > Input Sources.

The hex code for theta (θ) is U+03B8. So, to write theta (small - not capital), type 03B8 while holding the ⌥ Option key.

Additional info

The hex code for the capital theta (Θ) is U+0398, so typing 0398 while holding the ⌥ Option key will write it.

Quite surprised no one mentioned using the Unicode Hex Input keyboard layout.

You can add the Unicode Hex Input keyboard layout in System Settings > Input Sources.

The hex code for theta (θ) is U+03B8. So, to write theta, type 03B8 while holding the ⌥ Option key.

Unicode Hex Input keyboard layout

You can add the Unicode Hex Input keyboard layout in System Settings > Input Sources.

The hex code for theta (θ) is U+03B8. So, to write theta, type 03B8 while holding the ⌥ Option key.