Any guesses as to the CSS pixel width required to make a responsive design look good on Apples fancy new watch?

The company I work for has a visual designer for creating responsive and reflowing emails, and we think it would be pretty cool to support these watches and other micro-readers.

There will be few users at first, but having email that displays perfectly could be a huge part of inbox survivability (making sure the email shows well enough to not be swiped into oblivion, and hopefully be read or clicked on later on a larger device).

Thank you,
Seth