how far to drive every day

As so well put in the prior replies, find a comfortable distance and time frame but be willing to change it to meet your daily desires. We are heading from Seekonk Ma to Olympic NP (via US Route 2)then down the coastal highway some, then turn left at some point and drift back home this summer. We're figuring 12 weeks for this trip. I'm planning 225 miles per day however as I'm mapping it out I see days that will be 150, because We want to stop and site see, and others 250/300. We stop for 1 day after driving for 5 days. Just to take a break. We are planning on a week at the Glacier NP. I don't know how far down the west coast we will get, but there is always (God willing) next year. The bottom line is to enjoy yourselves. There is so much to see in this beautiful country of ours.