How much is it appropriate for a son and girlfriend to send a red envelope?

Your son's girlfriend's birthday depends on how they get along. If you have a good impression on her and they get along well, you can send a red envelope of several hundred yuan or 1000 yuan.

If she often goes to your house, you can also give her a smaller red envelope. I'm sure she won't ask too much. If you give too much, you will be lucky to send something like 288 or 688. Finally, it will be given to her according to your family's economic ability, and she won't mind more or less.