How Much Should I Weigh? – A Guide to BMI

bathroom scaleOne of the main tools for determining how much you should weigh, for the average person in an average health and fitness or training situation, is BMI, or body mass index. BMI is easy to calculate using height and weight measurements, and there are also physical tools (such as a caliper) that can take a physical BMI measurement.

What is BMI?

The BMI chart takes into account a person’s height and weight to determine the fatness level of the body. It is not a diagnostic tool, merely an initial screening tool that can guide a person (or a person’s doctor) toward a closer examination of possible health concerns regarding excess weight. It is not highly exact and it is not a direct measure of fat, but research does indicate strong correlations between BMI and more scientific measurements of fatness including measuring the body’s water displacement. It is often used because of its ease and its relative accuracy.

A person’s BMI is roughly calculated by a formula. In pounds and inches, the formula is [ weight in pounds / (height in inches x height in inches) ] x 703.

How does gender affect BMI?

It’s important to keep in mind that BMI is not an exact diagnostic measurement. It’s more of a guideline for screening for risk factors for certain diseases through an expression of correlations between height and weight. As such, gender differences in BMI’s accuracy do exist. Generally speaking, a woman will have more body fat than a man when the two have the same BMI. In fact, one study showed that women tend to have over 10% more body fat than men who have the same BMI. This is thought to be from the extra fat stores that women carry, which are associated with the ways that the female body is biologically equipped to sustain a full-term pregnancy. It’s from these extra stores of fat that a woman’s body derives nourishment for the pregnancy and the high fat content necessary for producing milk.

Despite the understanding that women have more stored fat than men at the same BMI, the World Health Organization and much of the medical community in the U.S. uses the standardized BMI charts for the sake of ease and simplicity. After all, BMI is not the “be-all, end-all” measurement when it comes to health, but rather a quick screening tool for identifying and determining the real risk factors that come along with overweight and obesity.

How does age affect BMI?

Similarly to the real differences noted in body fat between men and women who have the same BMI, people who are older tend to have more body fat than people who are younger with the same BMI.

What about kids?

With childhood obesity rates on the rise and more and more teens struggling with their own weight issues, BMI could be a useful resource for determining whether or not a young person is on an unhealthy track. As with adults, however, use the BMI as a guiding tool and not an ultimate word on whether or not someone is healthy. There are many factors to consider, and BMI is a good place to get started but not necessarily the only thing to consider.

BMI is calculated using the same for children and teens as for adults, but the results are interpreted very differently. Because children and teens are still undergoing rapid growth and changes in their musculoskeletal systems, there are separate BMI evaluations for these younger ages. These separate BMI interpretation charts take into account the child’s age and gender in the initial determination of whether he or she is at an appropriate weight. Having higher rates of body fat as a child is important for continued growth, for example, so a BMI that would indicate overweight in an adult would be considered very healthy for a young child. If you are evaluating the body mass index of a child or teen, it is important to be sure you are looking at the right chart.

What do I do with my BMI?

BMI primarily serves as a screening tool for weight problems, whether it is too little or too much weight. In the U.S., it is much more common for BMI to indicate overweight than underweight, though this is not necessarily the case in other parts of the world. If your BMI lands you in the overweight or obese category, you may want to take a closer look at your lifestyle and see if there any changes to be made.

As it has been stated before, the BMI is not an absolute measurement or a diagnosis. It is not a perfect tool and it should not be regarded as such. Highly trained athletes who are loaded with muscle and have very little fat, for example, can have a BMI that indicates obesity. And while being “big-boned” is sometimes used as an excuse for justifying a little too much weight, it is certainly possible to have bones that are heavier or lighter than average, so it is important to listen to your own body when you claim a certain weight or BMI as a goal; it could be that your goal should be higher than the chart says, and it could be that the goal should be lower. Evaluate your own BMI according to what you know about your body.

BMI is not the final word on your health

The body mass index chart is intended to be an easy-to-use guideline. It offers a quick way of determining whether a person is at a healthy weight or not, but it’s not diagnostic and it is not the last word on what a healthy weight is for you. It serves as a screening tool for overweight and obesity, but it is not an absolute sentence as far as health goes. Use your BMI as a beginning place to determine your overall health, but don’t automatically be discouraged if it is not what you want it to be. Listen to your body and evaluate your health according to how good you feel, how you look, or what the ideal weight for you is based on your own intuition.

Every body is different, and the body mass index chart is designed as a one-size-fits-all tool. It is very useful in that it gives doctors and other medical practitioners a starting place for determining health and beginning the appropriate discussions, when necessary, but it is by no means the only number or factor to consider for your health.