Android - Viewing distance in Google Fit
Good news! As of May 13, 2015, Google Fit was updated to show more kind of data: calories burned and distance. Note that the distance is approximated.
On the main screen, select the right drop-down list to change from active time/steps to distance, or tap/slide the big circle diagram to the second point.
You can also set the units to kilometers/miles in the settings.
(Image courtesy of Google)
At current there is no way to view distance, however it will probably come in a future update.
However you could calculate it by multiplying your steps by your average stride.
You can get your average stride by walking 10 metres, counting how many steps you take, and divide 10 by the number of steps.
One thing to bear in mind about google fit, is that it isn't designed to track say, where you went on a run, it is designed to do low power, background tracking and this is probably why there was no distance feature to begin with.