Difference between using Hi and Hey?

Solution 1:

As a greeting, Hey is more informal than Hi. I wouldn't use Hey in an office e-mail.

Hey is not considered childish or girlish. Most commonly used amongst young men I'd guess.

Solution 2:

E-mails

Hey or Heya are much less formal. You could use them if you were writing to friends.

Hey Dave, not spoken to you in a while. How're things? What've you been up to?

You could possibly use it in a more casual email (like a single question) to a colleague that you speak to often:

Hey Bob, just wondering if you've had a reply from Customer X yet?

Hi is the standard greeting for office e-mails. If you're not sure, stick with Hi.

Hi Dan,

Thanks for the information on [foo]. Do you know whether item 10 is for all customers or just Y?

I'll get back to you on [question] when I've had more time to look at the data.

Regards,

George

You could also use Hi for friends.

Conversation

Hey or Heya can be used to greet people you already know. Friends or colleagues. It's warmer than Hi so probably isn't suited to colleagues that you're less close to.

• Hey Dave, glad you could make it. How're you?

• Hey guys, what's up?

Hi can be used to greet people you already know, or those you don't.

• Hi Bob, how's Sylvia?

• Hi Kate, nice to meet you. How do you know Dan?

There is no gender differentiation in who can say either term, or who they are said to.

Solution 3:

Hi is used to greet someone and is a shortened version of hello. "Hello George". "Hi Mary". Hey was used to beckon someone. "Hey boy! Come here!". It is in recent times that Hi became too formal whilst meeting friends and Hey somehow found it's way into such colloquial meetings. "Hey Mary, How have you been?" If you are going to be using the written word or an email, stick to using Hi.