Method: 1 Alt Code
Θ (lowercase theta symbol) ALT + 952
Θ (Uppercase theta symbol) ALT + 233
Method: 2
Lowercase Theta Code: θ (03B8 and press ALT + X)
Uppercase theta Code: Θ (0398 and Press Alt + X)
Method: 3
Θ (Character Map)
Method: 4
Θ Character Code: 03B8
Θ Character Code: 0398