Body Mass Index (BMI) is a measure that compares a persons height to their weight. Because BMI is easy to calculate and explain it is widely used in identifying weight problems.  While indicative of body fat BMI doesn't directly measure it (so if you are mostly muscle, BMI is both misleading and ineffective).

BMI Calculator
Weight  Pounds  
Height Feet Inches

Use the chart below to plot the number from above calculator and figure out if you are underweight, healthy weight, overweight, or obese.