Both your weight and body composition are important for good health. No ideal body weight exists for anyone, but rather there is a range of acceptable weights for any given height. A doctor can advise you on whether you're at a healthy weight or have an increased risk of obesity-related health problems.
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Determining Ideal Weight
For women, an easy-to-use system for determining your ideal weight involves starting with 100 pounds for the first 5 feet of height and then adding 5 pounds for each additional inch. If you're a man, start with 106 pounds for the first 5 feet of height and then add 6 pounds for each additional inch. This means a 5-foot, 5-inch tall woman has an ideal weight of 125 pounds.
If you've got a smaller or larger frame, however, you'll need to adjust this ideal weight. Add 10 percent for a large frame; subtract 10 percent for a small frame. Men at least 5 feet, 5 inches tall have a medium frame if the wrist measurement is between 6.5 and 7.5 inches, and women of the same size have a medium frame with a wrist size between 6.25 and 6.5. A slightly shorter woman between 5 feet, 2 inches and 5 feet, 5 inches tall has a medium frame with a wrist measuring from 6 to 6.25 inches. The woman would have an ideal weight of about 113 pounds if she had a small frame instead of a medium one.
Healthy Weight Range Using BMI
Body mass index may better determine whether you're at a healthy size than an ideal weight calculation, because it provides a range of acceptable weights. It's easy to use a BMI calculator, or you can use the formula (weight in pounds / ( height in inches x height in inches ) ) x 703. Any result between 18.5 and 24.9 is within the recommended range. For example, if you're 5 feet, 3 inches tall, you should weigh 107 to 135 pounds.
Target Weight Using Body Fat Percentage
BMI doesn't take into account body fat percentage or distribution of body fat, both of which can affect your health. If you know your current body fat percentage and have an ideal body fat percentage as a goal, you can figure out what weight you'd need to be to achieve that goal. Your weight times percent of fat will tell you how many pounds of fat you have. Subtract this from your total weight for your lean weight. Subtract your desired body fat percentage from 100 percent, and then divide your lean weight by this number to get your target weight. For example, a person with 30 percent fat who weighs 150 pounds but wants to lower her body fat by 5 percent would use the following calculations: 150 x .30 = 45, 150 - 45 = 105, 105/(1.00-.25) = 140. She would need to lose 10 pounds of fat to reach her goal weight of 140 pounds and 25 percent body fat.
Calories Needed for Ideal Weight
Once you know what weight you're aiming for, you can calculate how many calories you'd need to sustain a body that size. A quick way to estimate calorie needs at your ideal weight if you're a man is to multiply weight in pounds by 14 to 18, choosing the lower number if you are sedentary and the higher number if you are very active. For women, multiply by a number between 12 and 16, depending on activity level.
A more accurate calculation requires calculating your basal metabolic rate, which is easiest when using an online calculator, and then multiplying it by an activity factor. If you're inactive, multiply BMR by 1.2, and if you participate in light exercise, multiply by 1.375. The activity factor for moderate exercise is 1.55, and for very active people it's 1.725. If you're very active and have a physical job, you multiply by 1.9. For example, a 5 foot, 3 inch tall, 35-year-old woman who weighs 140 pounds has a BMR of 1,396 calories per day. If she's moderately active, she needs about 2,164 calories per day to maintain her weight.
Calories for Weight Loss
If you're trying to get to an ideal weight, one way is to eat the number of calories needed to maintain that weight. Just plug the ideal weight into the BMR calculator instead of your current weight. Another method would be to calculate your current calorie needs and subtract between 500 and 1,000 calories per day, which causes weight loss of 1 to 2 pounds per week. Don't go below 1,800 calories per day if you're a man and 1,200 calories per day if you're a woman, however, because this can slow down metabolism and make weight loss more difficult.