What you should weigh depends on many factors, including your age, your gender, & your bone structure. Also, BMI is affected by gender. A newer measure that is becoming more & more recommended as a way to judge how healthy is your waist to height ratio. You divide your waist measurement in inches by your height in inches, to get a number. That number should be .50 or less. So since you are 64" tall, your waist should be 32" or less.