Cooking time estimates help plan out meal prep, but they are only estimates. The size and shape of your roast, your oven's performance and the type of roasting pan affect cooking time. Knowing your top round roast weighs 4 pounds and choosing a 350-degree Fahrenheit cooking temperature allows for a solid approximation, though. The only other significant variable is the doneness you're cooking to. The USDA recommends cooking to medium, but this lean, tougher cut turns out better at medium-rare.
A boneless beef cut like a top round roast typically takes 30 to 35 minutes per pound to reach the USDA-recommended temperature of 145 degrees Fahrenheit when roasted at 350 F, a total of 120 to 140 minutes. To cook it to medium-rare, or 135 F, subtract about 7 minutes per pound, for an estimated cooking time of a little over 1 1/2 hours. To cook the top round to medium-well, or 155 F, add about 7 minutes per pound to the medium estimate, for an approximate cooking time of a bit more than 2.5 hours.
Go By Temperature
Because the meat's internal temperature is a fixed number, while cooking time is variable, use a meat thermometer to determine doneness definitively. Insert it into the center of the thickest part of the roast. Also, the temperature of your roast rises 5 to 10 degrees during resting after you cook it, so take this into consideration when determining when to pull the meat from the oven.