The formula for calculating standard weight is weight (kg) = height (kg) – 105cm. 173cm boy’s standard weight is calculated to be 68kg. There are various ways to calculate the weight formula, you can use (height cm – 80) x 70% to calculate, if in the standard ± 10% range is normal weight. Within the range of ±10% to 20% there is overweight or underweight. Above the ±20 % range is considered underweight or overweight. Being overweight or underweight is not good for health. If you are in good health, you should be able to control your weight within the normal range without being overly strict about your ideal weight. Proper diet and exercise can help in weight control.