There is no duration on how long you should text a girl before you decide to ask her out.
It takes common sense you know if the chemistry feels right between you both and how deep your conversation is through the messages you exchange with her.
A girl that is into you will give you multiple signals through her messages and physical contact with you.
From the messages you exchange with each other, you can have an idea if she wants to take things slow or take her friendship with you to another level.
The moment she begins to reveal personal matters, desires, and emotional needs to you over text messages and physical meetings, it is a good sign that she trusts you more and will not mind going on a date with you.
At this point, it makes sense to ask her out through text messages, a phone call, or in person.
Text messaging is a tool that can either work for you or against you in your quest to get this girl to go out with you.
When used properly, it can be very effective, but for some ladies not asking them out in person may seem weird.
It doesn’t mean text messaging will not work for such girls but crafting it in a way that gets their attention will surely get them to go out with you.
Like I said earlier, try to understand the person you’re dealing with, probably with the contacts and discussions you’ve had with her and the kind of messages she sends to you.
If she’s the kind of person that wants to take it slow, sending her a text message to go out on a date with you might come out as being too fast, too early on.