How can you tell if you're skinny or fat if you have body dysmorphic disorder?

BMI. Probably the best resource for comparing your perceptions of your weight to "reality" is the body mass index calculation. There are several sites on the web where you can put in your weight, height, etcetera and get a value for your bmi which allows you to compare yourself to others. If you are very worried about your weight and it is close to the normal range, you might have a body image problem.