Pop-up thermometers are perhaps most commonly associated with roasting whole turkeys, but they can also be used to cook roast beef to within 2 degrees Fahrenheit of the desired temperature. Instead of probing the meat with a thermometer periodically, pop-up thermometers stay in the meat until the firing material inside dissolves at the desired temperature and the stem pops up. You can purchase pop-up thermometers to cook meat between 138 F and 203 F, which makes them useful only for medium to well-done beef in the ranges between 140 F for medium and 160 F for well done.
Select a pop-up thermometer that reads to the desired temperature level depending on how you prefer your roast beef. Medium roast beef should register between 140 F and 145 F; medium well roast beef is 150 F to 155 F; anything above 160 F is considered well done. Pop-up thermometers come in different lengths, so choose one that can reach to the center of the beef roast.
Push the pop-up thermometer into the beef roast at the thickest part. The end of the thermometer is pointed, resembling a golf tee, so it should push in easily.
Place the beef in a roasting pan and place in a preheated oven. The temperature of the oven depends on if you prefer to cook the meat slowly at a low temperature or faster at a high temperature. As a general rule, tough, lean cuts of meat such as a chuck roast should be roasted at a lower temperature to tenderize the meat, while naturally tender cuts such as a roast beef tenderloin can be cooked at a high temperature.
Monitor the oven and remove the roast when the stem pops up to indicate the inside of the roast is at the desired temperature. This takes roughly 25 to 30 minutes per pound when roasted in a 350 F oven, but the time differs in a hotter or cooler oven.
Set the roast on a serving plate and allow it to rest for at least three minutes to redistribute the juices.