If you only eat crackers will you lose weight?

Well crackers will make you lose weigth only if you are 1500 stones so be quiet and look young

A balanced diet and exercise would be much more effective but as long as the calories you consume are less then the calories you burn and baring any medical anomalies or complications you would most likely loose weight. You might not feel very well. In order to know your daily cracker intake you would have to know how many calories you burn during the day and then adjust your cracker caloric intake accordingly. The higher the fat content of the crackers you eat the less of them you will need to consume. This is not a recommended diet for a healthy living mammal.