Optimum distance between fields (Textboxes etc) on mobile touch screens

Question

What should be the optimal distance between fields such as Text boxes in mobile touch screens?

In order to avoid wrongly touching other fields.

^{download bmml source – Wireframes created with Balsamiq Mockups}

Answer 1

The question should not be about the gap between the fields. The fields can even touch each other if they're high enough, like on your mail app.

The height of the hit area (field height + half the gap of each side) should be at least 7mm, and in PX - that depends on your screen density(read this)

^{download bmml source – Wireframes created with Balsamiq Mockups}