Where to Start When You Want To Change Your Body and Your Fitness? Know your numbers!

This is a more in depth version of a previous post, “Know your numbers! Body Fat, BMR, and other tools to help you succeed!

If you look in the mirror and have finally accepted the fact that your clothes don’t fit anymore…  Or, you walked up one flight of stairs finding yourself out of breath and winded, you know it’s time to make a change.  These things aren’t going to get better by themselves.  You realize they’ll probably keep getting worse if you don’t course correct now.

If you’re ready to start the process of losing weight and gaining fitness, you may think looking at your bathroom scale is the best place to start.  Guess again.


You cannot manage what what you cannot measure.


The first step to getting your body under control is by knowing your numbers.

Many people get discouraged because they start gung-ho on a fitness program only find that they gain weight instead of lose it.  Other people start a diet program, lose some weight at first (not as much as they hoped) and then, even with all that hard work, the scale will no longer budge.

This is what happens if you don’t know some of your key numbers when you start.  By numbers I mean:

  • Percentage of your body weight that is fat
  • Percentage of your body weight that is lean mass (i.e. muscle, bone, organs and water)
  • Your BMR (basal metabolic rate) which is how much energy your body spends just to exist.  Imagine you are laid up in bed for 24 hours doing nothing more than blinking and breathing.  However many calories it requires for your body to do this is your BMR.
  • Your BMI.  This is just a general ranking that tells you if you’re obese, overweight, normal or underweight based on your height.

Knowing these numbers when you start will help you understand if your body is improving (or not, even when the scale gets stuck.  Just going by the scale can be very deceiving, or even demoralizing.

The more you increase muscle and decrease fat, the higher your BMR will be because muscle requires more energy (calories) to maintain itself than fat does.  You may already know that muscle weighs more than fat.

Will You Be Exercising, Dieting or Both?

It’s not unusual for someone to start a fitness program and see the numbers on the scale go up rather than down.  One possible reason may be that some people build muscle faster than others.  Another is that some people do not burn fat efficiently.  While another reason, which is all too common, is that some people tend to eat more when they start an exercise program, thereby taking in more calories than they’re burning.

People who choose dieting as their main method for weight loss will often lose muscle along with fat.  That looks good on the scale, but may not be the best thing if you’re trying to increase strength or performance.

Of course the fastest path to success is combining an exercise program with a diet that promotes muscle gain and fat loss.

What are the best ways to find my numbers?

If you’re not sure if you’re if your body weight is in the healthy range for your height, start with your BMI. Click here for a BMI (body mass index) calculator.

Now let’s go deeper.


checking my body composition on the InBody machine at my gym

Body Composition

There are a few ways to determine your percentage of body fat and lean mass.  Some are easier, cheaper (or free) but may be less accurate.  Some cost a bit more and are very accurate.  All of them only take a few minutes.

  1.  For free, easy estimate, you could try this online calculator.   All you need is a tape-measure.  It’s hard to know how accurate this is because different calculators use different equations.  But if you stick with the same one and check somewhat regularly, you can see your progress even if the numbers aren’t exactly right.

2.  You can ask a skilled trainer who has skinfold calipers to measure you.  This is a method where someone pinches your body fat at specific sites with a caliper and plugs the numbers into a formula.  Your results can be affected by the brand / type of caliper (metal or plastic), the experience of the trainer and, what body sites they measure.

There is usually no set price.  It may be offered for free with purchase of a training package, or it may be a fee you can negotiate.

3.  Many gyms and sports facilities offer testing through Bioelectrical Impedance Analysis (BIA) machines.  This service may or may not be free.  There are also home versions like this one that are around the $100+ range.   This method simply requires you stand on the machine.  BIA  measures body composition based on the rate at which an electrical current travels through the body.  Body fat creates more resistance than fat-free mass which slows the speed of the current.  Your hydration level can mess up your reading.  For example, after a hot, sweaty workout, your body fat may read higher than if you measured yourself before.

Prices vary depending on whether you do it at a fitness facility or buy a home version.

4. DEXA Scan.  The DEXA scan uses X-ray technology while you lie on a table.  It is considered the gold standard and most accurate method for measuring body composition.  It  will not only show your percentages of body fat and lean tissue, but also your bone density which is extremely important.  It will further break down the measurements for both legs, arms and the torso so you can see how your body fat and muscle is distributed.  Another huge advantage is it shows how much visceral fat you have.  This is the dangerous type of fat that surrounds the organs and disrupts hormones.  The higher amount of visceral fat you have, the greater your risk for serious health consequences.


Body composition


Price ranges from moderate to high depending on the facility.

5. Hydrostatic weighing.  This is affectionately known as the “dunk test” and is one of most reliable methods for testing body composition.  It works by calculating water displacement based on the fact that muscles and lean tissue are denser than fat.  The downside is you have to hold your breath and get wet.

Price range is moderate.

6. BodPod.  This is a device that determines body fat based on how much air is displaced when you sit in the pod.  The concept is similar to hydrostatic weighing, but not as accurate.  A study published in 2015 showed that accuracy varied significantly based on whether a person was normal weight, under weight or overweight. The study found that the bod pod was more accurate when testing people who had a healthy BMI.

Price range is moderate.


How Many Calories Should You Eat a Day?

Finally, to estimate how many calories you should be eating a day, you will want to calculate your BMR.  If you eat approximately the same number of calories as your BMR, you will almost assuredly lose weight (some may come from muscle loss if you diet only).  If you exercise, you adjust those calories up.  Of course, other factors may play a role in your metabolism such as hormones, genetics, certain medications, diseases, and the type of foods you eat.

For an easy way to get a rough estimation, you can use this free BMR calculator.  The NIH (National Institute of Health) recently launched a more comprehensive, free calculator and tracker you may want to try.

To get a precise picture, you can have metabolic testing done in a lab or at your gym.  This requires using a mask that measures your oxygen consumption while running on a treadmill or cycling on a stationary bike.  If you have the opportunity to do this, go for it!

How often you test yourself is completely up to you and your goals.  Go get ’em!

Jill Brown
Jill Brown
Hi, I'm JillI am a Los Angeles based Fitness + Nutrition Coach. With 20+ years of experience in teaching, training and continuing my education, I have transformed thousands of lives through fitness and healthy lifestyle changes.