Lean Body Mass Calculator

Why should you measure lean body mass?

If you're looking at how to build lean muscles, it can be very useful to know your lean body mass. It’s a great indicator of overall health, adding some much-needed detail to more conventional measures of weight like BMI. It can help you to decide on your health and fitness goals- if you’re looking to lose weight, build muscle or maintain a healthy body composition, it will be the measure by which you plan a great deal.


But what is it, and how is lean body mass calculated? Let’s take a look.


What is lean body mass?

Lean body mass is your overall weight minus your weight from body fat. Basically, if you subtract the weight that comes from fat (your body fat percentage) from your total weight, you will have your lean body mass.

Knowing this can help those looking to lose weight maintain their weight loss purely from fat. If you can keep your lean body mass stable whilst bringing your overall weight down, you will know that you’re only losing fat- not muscle or bone density, as is often the case.


Alternatively, those looking to put on weight in the form of muscle will want to build their lean mass at the same rate as their overall weight. This will show them that, although they are gaining total weight, they are not putting on any extra body fat.


To find out your lean body mass, you often need to know your body fat percentage, though we will run through some methods below in which this isn’t the case. Some of the methods of lean body mass calculation are more accurate than others, whilst some are more accessible, though we will run through these all shortly.


How is lean body mass calculated?

There are two main ways in which lean body mass is calculated. There is often a trade-off between accessibility and accuracy, with the most accurate methods being beyond many people.


1. Using your weight and height

This is arguably the most accessible, crudest way of finding out your lean body mass. There is a simple formula you can use for which you will only need your weight and height. Use the equations below, with all weights in kg and all heights in cm.


  • For men: Lean body mass = (0.32810 × W) + (0.33929 × H) − 29.5336
  • For women: Lean body mass = (0.29569 × W) + (0.41813 × H) − 43.2933

It should be noted that this will be quite inaccurate but may work well as a rule of thumb or best guess in the first instance.


For an easier version of this, you can always choose an online calculator for lean body mass like the one below.


2. Using your body fat percentage

You can also use your body fat percentage to work out your lean body mass, as mentioned above. Divide your percent body fat by 100 to make it a decimal. Then multiply this number by your total weight.


For example, if you weigh 80kg and have learned that your body fat percentage is 15%, multiply 80 x 0.15. This is your fat mass in kilograms (800 x 0.15 = 12kg). Then simply subtract this from your total weight to get your lean body mass. Here, we are looking at 80 - 12 = 68kg of lean body mass.


The tricky part here is finding out your body fat percentage. The techniques below will all enable you to do so but the trade-off mentioned above comes into play: generally, the more accurate the method, the less accessible it is to most people.


Methods of finding out your body fat percentage include:


Skinfold assessment

Use skin fold calipers on a range of points on your body. You will pinch the skin and measure the thickness, then simply put these numbers into a conversion table or calculator for lean body mass.

Many personal trainers at your local gym will be well-practiced in this technique. It’s not the most accurate method but is easy and relatively reliable and consistent.


Bioelectrical impedance scale

Again, your local gym may offer this facility. A bioelectrical scale is a set of scales with electrodes that you stand on, and/or grip in your hands, as they send a gentle electrical current through your body. As muscle and fat conduct electricity differently, they will tell you everything you need to know. They are safe, though not always accurate (other factors, like hydration, can sometimes skew readings).


Hydrostatic weighing

This is where we get very accurate and very inaccessible. Hydrostatic weighing involves a comparison between your weight on land to your weight while completely submerged in water. A technician can then calculate your body fat percentage.


As before, it’s very reliable: however, it involves large amounts of specialist kit, will not be available at your local gym, and can cost a fair amount.

Lean Body Mass Calculator

Body Fat Percentage

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