The distance between Boston, Massachusetts, United States of America and Portland, Oregon, United States of America is approximately 3,100 miles which equals to approximately 5,000 kilometres. If you are thinking of going to Portland via road, it is really not advisable as it will take nearly more than 48 hours in order to get there. Portland lies on the west coast of America and Boston lies on the east coast of America and you would have to go from end of the country to another completely across America. It is advisable to go by flight or train as you will reach much faster.
There are daily local flights from all the airports of America and the flight tickets are quite cheap as well so that you should not have any kind of a problem reaching your destination.