A device for measuring the Body Mass Index (BMI) of an adult, providing a measure of weight for height. The device allows for an easy and quick determination of BMI or the adult weight status. The device consists of a hand held slide ruler instrument on which a combination of an adult's weight and height immediately indicates the corresponding BMI. Using this device, an adult over 18 years old can determine how much weight he/she would need to lose or gain in order to achieve normal weight, as specified by the current US government guidelines.