It's no secret that weight can affect your health, but it's not enough to measure weight alone. You also need to look at both your weight and height -- or what some people call your "weight-to-height ratio." Although it's not a true ratio, your body mass index -- or BMI -- takes into account weight and height and contains standardized measurements to give you an idea of whether you're at a healthy weight.
Weight, Height and BMI
The easiest way to figure out if your weight is appropriate for your height is to calculate your body mass index, or BMI. BMI takes into account both your weight and height, plus a conversion factor that allows you to use Imperial measurements -- pounds and inches -- instead of kilograms and meters.
Use this formula to figure out your BMI: BMI = 703 x [(weight in pounds) / (height in inches x height in inches)]
For example, a person who weighs 180 pounds and stands 6 feet -- or 72 inches -- tall could calculate his BMI by putting his numbers into the equation:
BMI = 703 x [(180) / (72x72)]
And figure out that his BMI is 24.4.
Healthy Weight-to-Height Ratios
Once you know your BMI, you can use BMI standards to determine if you're at a "normal" or healthy weight. You're at a normal, healthy weight if your BMI ranges from 18.5 to 24.9 -- for someone who is 6 feet tall, that would be between roughly 140 and 183 pounds.
If your BMI is above 25, you're considered overweight for your height; if you have a BMI over 30, you're considered obese for your height. On the other hand, if you have a BMI of 18.5 or less, you're considered underweight based on your weight and height.
The Shortfalls of Measuring Weight-to-Height
While your BMI provides some insight into whether you're at a healthy weight, it doesn't tell the whole story. If you're very athletic and muscular, for example, you might have a higher-than-normal BMI due to your extra muscle tissue, but you're not actually carrying excess body fat.
On the other hand, if you have very little muscle tissue, you might be overfat -- and face a higher risk of weight-related illness -- even at a healthy weight for your height. As you age, you're more likely to carry too much fat even if you're at a "healthy" weight, since you'll likely to lose lean mass, like muscle and bone tissue, and gain fat. So while your weight provides some insight into your health, it's not the only factor you should consider.
Other Factors to Consider
Consider incorporating waist measurement into your fitness tracking routine. A larger-than-healthy waist size -- which is 35 inches for women and 40 inches for men -- likely means you're carrying too much visceral fat, which ups your risk of chronic obesity-related illness.
Waist-to-hip ratio -- calculated by dividing your waist size by your hip size -- also offers some insight into your health. A larger-than-healthy ratio -- greater than 0.9 for men or 0.85 for women -- indicates you have an "apple" shape, so you store excess fat in your belly, and might face a higher risk of disease because of too much visceral fat.
For the most accurate -- and a fully personalized -- assessment, talk to your doctor or other healthcare provider. They can take waist and hip measurements, as well as measure your body fat levels using body scans or weighing methods -- like underwater weighing or DEXA scans -- not available at home. A professional can also recommend a nutrition and fitness program to address any health concerns, based on your body fat levels.