Lean Body Mass Calculator

Estimate your Lean Body Mass

If you are an active person, you’ve likely heard a few things about muscle mass. Even if you’re not that active, you probably have that friend who’s always working out to put on some lean muscle. What most people are really referring when they use these terms is their lean body mass, or lean mass. By deciphering your lean mass from your fat mass, you can get a better idea of what’s really going underneath your skin.

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Lean body mass
What is lean body mass?

Lean body mass (LBM) refers to the part of your body that is made of fat-free mass, as opposed to fat mass. More specifically, lean body mass can tell you the weight of your bones, blood, organs, muscles, and body water. By considering the difference between your total weight and lean mass, you can also illustrate what portion of your body contains fat.

For example, a 27-year-old female, weighing 105lbs and measuring 5ft2, would have an approximate LBM of 84lbs. Subtracting that from her total weight can tell you that she has about 21lb of fat (105lb total mass – 84lb fat-free mass = 21lb fat mass) or 20% body fat. (21lb fat mass ÷ 105lb total mass x 100 = 20%).

So the next time a friend tells you they’ve made 5 pounds of lean gains, what they are trying to say is they increased their lean mass by five pounds (hopefully). Unless they tested their body composition, there’s no way to relate what caused the change in weight. When it comes to weight gain, there can be many factors at play.

Why is lean body mass significant?

Lean body mass is a person's body weight minus their fat mass. The weight of your organs and bones won’t change much over time, at least not significantly. That means most fluctuations in your lean mass will be due to your muscle tone and body water. However, that’s not always the case with weight gain.

Sometimes, weight gain can be due to variations in your health or lifestyle, such as improper nutrition, hormonal changes, and starting certain medications. In these scenarios the body stores energy instead of using it, despite your best efforts. Measuring your lean mass can help you understand what’s going on beneath the surface – whether a change in your weight is due to water retention, fat storage, or muscle tone.

In addition, finding out your LBM can help you identify your unique nutritional needs. If your goal is to lose weight, but not muscle, you’ll have to make sure your nutrition is on point. First, you’ll have to figure out the number of calories you should be consuming (start here, or here). Then you’ll need your LBM to find what portion your daily calories should go towards protein.

Studies have shown that it is optimal to get 30%-35% of your total energy from protein when you’re on a calorie deficit diet. When you convert that percentage of protein into grams, it equates to about 1.2 to 2.3 grams of protein per kilogram of LBM. Here's another study on the matter. When there is enough protein in your diet, the body can prevent muscle breakdown and stimulate muscle growth from the ingested amino acids.

How do you measure lean body mass?

There are numerous ways you can test your lean body mass that will vary in cost and accuracy. Methods that are less expensive (and less accurate) require callipers, a handheld myography device, or a measuring tape. Tests that are more costly, but still not wholly accurate, consist of DEXA scans, underwater density testing, and bioimpedance scales.

Skinfold test. You can purchase callipers online for a few dollars to take skinfold measurements. You'll test some areas of your body to get an average measurement of your subcutaneous fat. When you invert your body fat percentage, you can estimate your LBM.

Bio Impedance Analysis (BIA). There are many different BIA devices you can use to test your LBM. Accessories range from expensive stand-alone machines that you can find at a health facility to handheld alternatives you can buy online on a budget.

These devices move weak electrical currents through your body figure out your body composition. As the harmless pulse moves through the skin, fat, and muscle, it experiences varying resistance from the different tissues (more on this later). The device estimates your body fat and lean mass based on the amount of electric resistance. Higher resistance = higher fat content in tissues.

Electrical Myography. A handheld myography device also sends harmless currents between electrodes to gauge your lean mass. With this type of device you’ll measure various areas of your body by pressing a paddle on skin that’s moistened with water. The device will give you individual readings so you can see which areas of your body contain a higher (or lower) percentage of body fat and lean mass.

Dual-energy x-ray absorptiometry (DEXA). Dexa scans primarily measure the density and mineral content of bodily tissues. However, these scans can also provide notably accurate readings of body composition. The technology can estimate body fat percentage and measure amounts of visceral adipose tissue (VAT). Since VAT is thought to be a primary contributor to obesity-related health risks, this can be a valuable distinction to make.

Underwater density testing. Hydrostatic testing requires your body to be submerged in a tank of water. The amount of water displacement directly correlates with your fat mass and LBM.

Measuring tape. One of the simpler at home methods to measure your lean mass requires a measuring tape and a scale. You'll have to weigh yourself and then measure your height. You can input your measurements into various formulas to estimate your lean mass and fat mass. The calculator on this page is designed with Boer, James, and Hume methods for measuring LBM. However, since equations are developed by population averages, results should be used as an approximation only.

Which method is best?

The method of testing you select should reflect your priorities. If you are just curious about your body composition, you should start with skin fold tests and online calculators. As you become more invested in your wellness, you may want to try the BIA scale at your local health club or purchase a personal myography device you can use at home.

There are some instances where a professional body composition test could be of interest to you as well. When a doctor is a concerned about the effect your weight is having on your overall health, you’ll want to get a scan done before and after your weight loss efforts. Likewise, professional athletes or bodybuilders may also want a more exact measurement of their body composition to streamline their nutrition and training. There are even some pharmacology applications, such as dosing specific drug and anesthetics, where you'll want to know your LBM pretty precisely.

How accurate are LBM devices?

Of the testing methods already mentioned, professional scans and hydrostatic testing are the most precise, though not perfect. In fact, DEXAs and MRIs are the best way for an individual to find out their body composition. The alternative, BIA devices, can vary considerably in their accuracy. They have proven to deviate from actual levels of body fat and skeletal muscle by about 2-6% and 3kg, respectively (according to this study).

A meta-analysis done on electric resistivity provides evidence of some uncertainties regarding our ability to differentiate tissues through BIA. The study goes on to say that many tissues within the body are equally resistive, showing differences that are insignificant in many tissues . However, fat does display higher resistivity along with bone and skin. The resistance of fat tissue means that a current may be able to estimate your body fat percentage within a few points, but cannot entirely differentiate between organs and other bodily tissues – at this time.

How much lean body mass should I have?

Generally speaking, having higher LBM is healthier because of the role muscle tissue plays in metabolism. Muscle burns approximately 3.3 times more energy than a pound of fat, even when you are resting. Beyond that, your muscles provide you with the ability to move in all sorts of ways. Whether you like golfing, swimming, or cross fit, your muscles make it all possible.

There are three different types of muscle tissues within the body – skeletal, cardiac, and smooth muscle. Of these muscle tissues, skeletal muscle can grow with the proper nutrition and exercise. In fact, it's highly suggested to engage in some physical activity on a regular basis. Muscle tissue starts to degenerate after a person reaches 30 years old, especially when leading a sedentary lifestyle. The good news is that the degenerative condition of muscle tissue can be counter-acted through regular resistance training.

Using the calculator

The calculator is very straightforward to use - it has a questionnaire and a results section. You just need to add a few personal details to get an estimation of your lean body mass. Let’s review this information together.

Step 1. Before getting started, you should select the units of measurement you are comfortable with. You can choose between US units or metric units by selecting one of the tabs at the top of the calculator.

Step 2. On the first line of the calculator, please identify your age. You can use your keyboard or the arrow features to input this information easily.

Step 3. Next, you’ll have to select your gender, whether you are male or female.

Step 4. Then you’ll need to set your height and document your weight on the last two lines of the calculator.

Step 5. You can view your results in the table below the questionnaire. For more details on the formula used by this calculator, proceed to the next section.

Your results

This calculator is designed to calculate your lean body mass according to four different equations. Three of the formulas are tailored to adults, while one is made for children up to 14 years old.

Boer Formula
Male 0.407weight(kg) + 0.267height(cm) – 19.2
Female 0.252weight(kg) + 0.473height(cm) – 48.3
James Formula
Male 1.1weight(kg) – 128(weight(kg)/height(cm))
Female 1.07weight(kg) – 148(weight(kg)/height(cm))
Hume Formula
Male 0.32810weight(kg) + 0.33929height(cm) – 29.5336
Female 0.29569weight(kg) + 0.41813height(cm) – 43.2933
Peters Formula (for children up to 14 years old)
Children 3.8*[0.0215*(Weight in Kg^0.6469)*(Height in cm^0.7236)]