Best Practice for sizing a single line input?

Is there a good best practice when it comes to creating text boxes as far as height goes?

Should it be, in general, 1/15 the vertical height of the screen? 1/20th? 1/10th?

A text box that is 30 high is not the same on another device. [import]uid: 13784 topic_id: 30014 reply_id: 330014[/import]