The Royal Enfield Classic 350 typically requires approximately 2.75 liters (or 2.9 quarts) of engine oil for a complete oil change. However, it's essential to refer to the owner's manual or consult with a Royal Enfield authorized service center for the most accurate and up-to-date information on the specific oil capacity and recommended oil type for your Classic 350 model. The manufacturer's guidelines should always be followed to ensure proper lubrication and optimal performance of the motorcycle's engine.