How well cooked the meat is will depend now on how long you leave it in the oven (and on the characteristics of your oven). Broadly speaking 10 minutes is enough for "rare", 15 minutes for "medium" and 18 minutes or more for "well done". These times are very approximate and you can adapt them to your taste.
If you'd like something more precise and sure, stick an electronic thermometer into the middle of the meat. When the temperature reaches: