Add storyboard file.
In IB open Storyboard. Storyboard said "no scenes". Drag view controller into storyboard, now storyboard shows a scene.
In storyboard change view controller class to ConvertViewController.
In storyboard add text fields temperatureIn and temperatureOut. Connect to IBOutlets. Set temperatureIn field delegate to view controller.
In IB storyboard, delete 2 text fields from previous commit. In .xib file, copy content view and all contained objects. In storyboard, paste content view and contained objects.

This is so much faster than doing one at a time! Elements remember many of their settings from .xib.
TODO: Connect outlets, delegate.
In storyboard connect outlets, actions, and delegates.
In target Convert / Summary iphone deployment info Change project setting info from xib to storyboard.

Got error There is no app delegate set. An app delegate class must be specified to use a main storyboard file.
http://stackoverflow.com/questions/17278442/replace-xib-file-with-mainstroyboard-file-in-app-delegate-class
In main.m change return argument from nil to app delegate, import ConvertAppDelegate.h.
App works. Temperature fields appear smaller than before. This may be related to AutoLayout.
In storyboard text fields, increased minimum font size from 16 to 48. This fixed appearance.
Deleted ConvertViewController.xib. App still works and running scheme ConvertUnitTests passes.