Know your numbers! Body Fat, BMR, and other tools to help you succeed!

When you’re ready to take charge of your fitness, whether it be weight loss, muscle gain or improving athletic performance, it’s important to know where you’re starting out.   Knowing certain numbers is the first step to taking control and having a successful outcome.  What if you’ve already started your program but now feel like you are stalling or sliding backwards?  It’s never too late to get a picture of where you currently stand.

There is no failure.  Only feedback

  1.  Know your BMI.  Your BMI (Body Mass Index) will tell you how far off your are from the ideal or healthy body weight.
  2.  Know roughly (or precisely) what percentage of your body is fat and what is percentage is muscle and lean tissue.   This is called your body composition.
  3. Know your BMR. Your BMR (Basal Metabolic Rate) allows you to know about how many calories your burn a day at rest (lying in bed all day with the flu for example, just breathing and blinking).

So let’s get started with some basic calculators.

Use this free online calculator to determine your BMI.

This free calculator can help you estimate your percentage of body fat.  A tape measure is required.  Note that the numbers can be quite inaccurate if you are very muscular.

And here’s a BMR calculator so you know how many calories you can eat a day.  Remember, the more you exercise or stay physically active, the more you can add to that number.  But if you have a significant amount of weight to lose, simply try to eat around the same number of calories as your estimated BMR, and results should come.  A more comprehensive, free calculator and tracker is offered by the NIH.

Of course, it may not always be so simple.  Other factors may come into play like hormones, diseases, medications and your good old friend, your DNA.  These factors may make it easier or harder for you to drop fat pounds as fast as you like, or gain as much muscle as you want.

What if you want more accurate numbers?

If you want to dive deeper and get a more precise picture, then online calculators may not cut it for you.

Body composition


To get more accurate numbers, you will want to get a DEXA Scan.  The DEXA scan  uses x-ray technology and is considered the gold standard method for measuring body composition.  It  will not only show you your percentages of body fat and lean tissue, but it will also measure your bone density.  The DEXA scan print out will 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 that is tells you 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.  A DEXA scan only takes a few minutes and is done while you lie on a table.

Another reliable method for measuring body fat and lean mass is hyrdostatic weighing.  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 get wet.  It also doesn’t give you as much information as the DEXA scan.

Withings / Nokia Body-Smart scale

Body – Smart Weight & BMI Wi-Fi Digital Scale

Somewhat less reliable, but widely available is Bioelectrical Impedance Analysis (BIA).  There are commercial ones that you can find at gyms and fitness facilities.  And 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 speed an electrical current moves through your body.  Body fat creates more resistance than lean body mass which slows the speed of the current.  Factors like your hydration level can mess up your reading.  For example, if you test yourself right after a vigorous workout, of after you have  been sweating, your body fat may read higher than at a different point in the day.

The Bod Pod uses a similar concept as hydrostatic weighing.  It determines body fat based on how much air is displaced when you sit in the pod.  A study published in 2015 showed the accuracy varied significantly based on whether a person was normal weight, under weight or overweight.  According to the study, people who had a healthy BMI showed more accurate numbers than people with less healthy BMIs.  Bod Pod’s are also not as widely available yet.

Finally, you can use the old school method of skinfold calipers, usually offered by trainers.  This method involves having your skin pinched and measured with calipers at various sites on the body.  Accuracy depends on the type of calipers and the skill of the trainer.

Whichever method you choose, knowing some of these key numbers will help you be accountable to yourself.  And if you don’t see the scale moving in the direction you want (down), it could be because you’re gaining muscle.  This can help you stay motivated.  All too often people give up because the scale isn’t budging when in reality, they are actually getting fitter.

Don’t give up for the wrong reasons!

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.