How long is "a while"?

"You'll have to wait a while" usually means "You'll have to wait a long time."

Vam asks a very good question about the phrase a while.

Often the verb take is used with a while to show reluctance or difficulty in doing something:

In fact, it took a while for anyone to find the error.

You'll get used to it, but it might take a while.

It has taken a while for them to respond.

You can also use the verb to be: 

He's working on it now, but it might be a while before he's done.

You're welcome to wait, but it might be a while. 

It's been a while since I worked there.

A while also commonly follows prepositions:

I'll be back in a while.

It will be stored at my house for a while.

We left the party after a while.

Quite often modifies while:

I haven't had steak in quite a while!