Cooking time for boneless pork loin roast?

I have a 1 1/2 Lbs roast. I was planning on searing in a pan before putting it in the oven at about 250 degrees. Trouble is..I don't know how long to cook it, with the temp so low. The last time I tried, I cooked it a little long, and it was dry. How long do I cook the roast at 250 degrees?