Use Google's geocoding to convert addresses to GPS coordinates in a Google spreadsheet.
Install this to add an add-on to geoencode an address/location into latitude and longitude in a Google spreadsheet. To use, select a contiguous column of data to convert and choose Macros->Geoencode Selected Cells. The results are stored in the columns labeled 'Lat' and 'Lng'.
Google requires you to turn this on for every sheet you wish to use it. To enable go to: Add-ons->Manage Add Ons. Click "manage": next to Geocode Cells and select "Use in this Documenting"
See: https://support.google.com/docs/answer/3641454 for more info.
Note: This uses the Google geoencode API to do geoencoding, which has a strict limit on calls per day.