To supplement Matt's answer…

<h3>Are there other controls on the screen?</h3>

[Research shows][1] users have more confidence in a product—they believe the product is more accurate—when its visual elements are nicely aligned.

If there are multiple controls, or text boxes, sizing each one to fit its anticipated content (below, left) would be a poor choice. Look at the two options separately—so cover one side with your hand, then the other side.

[![Some ways to align controls][2]][2]

As always, different design goals will be in tension. Make an appropriate compromise.

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I hope that helps you move forward.


  [1]: https://scholar.google.co.uk/scholar?q=effect%20on%20user%20attitude%20aesthetics%20software&hl=en&as_sdt=0&as_vis=1&oi=scholart&sa=X&ved=0ahUKEwjC17enyrXJAhWHQBQKHQFrB68QgQMIIjAA
  [2]: https://i.sstatic.net/H4FM9.png