As a general rule, calculate a cooking time of 20 minutes per pound of meat plus an additional 10 - 20 minutes at a temperature of 375ºF (190ºC). Therefore, a 5 lb chicken will need to be roasting in the oven for at least 1h 50 mins. A 5 lb bird will serve between 4 - 5 people. Some people prefer to set the oven temperature to 450ºF (230ºC) and roast the bird at this high temperature for the first 10 - 15 minutes or the last 10 - 15 minutes.