St Louis ribs typically take around 5-6 hours to smoke at a temperature of 225°F (107°C). However, the exact cooking time may vary depending on factors such as the size of the ribs, the desired level of tenderness, and the consistency of the heat in your smoker. It’s important to monitor the temperature of your smoker and the internal temperature of the ribs using a meat thermometer to ensure that they are cooked to the appropriate doneness. You should aim for an internal temperature of around 195°F (90°C) in the thickest part of the meat, and the meat should be tender and easily pull away from the bone.