🐷 Body Fat Calculator

01. Two numbers — your weight and lean body mass — and you're done

There are only two fields to fill in. The lean body mass reading straight off your scale is all you need, with no measuring tape involved.

02. No estimation formula, so the figure reflects what you measured

Nothing is inferred from your height or age. The result is derived from the lean body mass you actually measured, so no estimation error creeps in.

03. The result updates the moment you change a number

Every edit recalculates the percentage, which makes it easy to nudge the figures around while you look for a target.

01. Basic Usage

1. Enter your weight (kg)
2. Enter your lean body mass (kg)
3. Your body fat percentage appears as you type

02. If You Don't Know Your Lean Body Mass

1. Check whether your body composition analyzer or InBody reading already lists lean body mass
2. If it does not, subtract your fat mass from your total weight
3. If you have no way to measure it, use the BMI calculator instead, which needs only height and weight

Q. What formula does this use?

A. (Weight − Lean Body Mass) ÷ Weight × 100. Because it uses your measured lean body mass directly, it avoids the error introduced by estimation formulas based on build or sex. This differs from methods that estimate from neck and waist circumference.

Q. Why is there no result when lean body mass equals or exceeds weight?

A. Such input would produce a body fat percentage of 0% or below, so no result is shown. Check your body composition reading and enter a value lower than your weight.

Q. What input range is accepted?

A. Both weight and lean body mass accept 5kg to 700kg. Values outside this range show an error message and produce no result. Decimals are accepted.

Q. Can I enter pounds (lbs)?

A. Only kilograms are supported. If your measurements are in pounds, convert them first using 1 lbs = 0.453592 kg.

Q. Are my entries saved?

A. No. Reloading the page clears the fields. Use a separate note or app if you want to track values over time.

Q. What is Lean Body Mass (LBM)?

A. The weight of everything in your body except fat—muscles, bones, organs, and water.

Q. How do I measure lean body mass?

A. Body composition analyzers (like InBody) measure this. They're commonly available at gyms and health facilities. Advanced home scales can also measure it.

Q. What's a healthy body fat percentage?

A. For men, 10-20% is standard; for women, 20-30%. Athletes may have lower values.

Q. What's the difference between BMI and body fat percentage?

A. BMI only uses height and weight, not distinguishing between muscle and fat. Body fat percentage shows actual fat proportion, enabling more accurate body composition assessment.

Q. How can I increase lean body mass?

A. Strength training and adequate protein intake are effective. Increasing muscle mass raises lean body mass and boosts basal metabolism.

01. Same Weight, Different Composition

Body fat percentage can vary greatly at the same weight. For example, at 70kg with 63kg lean body mass, body fat is 10%, but with 56kg lean body mass, it's 20%. The scale reads the same for both people, yet their physiques and health profiles differ entirely. This is exactly what chasing body weight alone hides from view.

02. Fat Is Not Merely Excess

Bodybuilders may drop below 5% body fat, but this is temporary for competitions. Some body fat is essential for healthy living. Fat isn't just 'excess'—it plays crucial roles in hormone production and temperature regulation. Absorbing and storing the fat-soluble vitamins A, D, E, and K also depends on it.

03. This Calculation Is Not an Estimate

This tool treats the difference between body weight and lean body mass as fat mass, then expresses it as a share of body weight — the very definition of body fat percentage. Because it is not a formula estimating from height, age, sex, or waist circumference, there is no estimation error to speak of. If the two figures you enter are correct, so is the result. The flip side is that you must already know your lean body mass from another source.

04. Where to Find Lean Body Mass

Most home body-composition scales display lean body mass alongside body fat percentage. Even without that readout, subtracting fat mass from body weight gives you the figure. More precise methods include hydrostatic weighing, air displacement plethysmography (the BOD POD), and DEXA (dual-energy X-ray absorptiometry). DEXA can separate bone, fat, and lean tissue, which is why research settings treat it as the reference.

05. How Body-Composition Scales Work

Home scales use bioelectrical impedance analysis (BIA), passing a weak current through the body and measuring resistance. It exploits the fact that fat conducts poorly while water-rich muscle conducts well. What the device actually measures, however, is resistance; converting that into a body fat percentage requires an estimation formula. Those formulas differ by manufacturer, so changing devices changes the number.

06. Readings Drift by Time of Day

Because BIA depends on body water, results shift between morning and evening on the same day. Readings tend to run high right after waking, when you are relatively dehydrated, and low after a bath or exercise. Meals, alcohol, and sweating move the figure too. If you are tracking progress, the rule is to measure under identical conditions every time — for instance, right after waking and using the bathroom. A series of comparable readings tells you far more than any single measurement.

07. Essential Fat Sets a Floor

The fat required simply to stay alive is called essential fat, roughly 3 percent of body weight in men and about 12 percent in women. The gap exists because women carry additional fat tied to reproductive function around the breasts, pelvis, and thighs. When a woman's body fat falls too low, menstruation can stop; the linked pattern of amenorrhea, osteoporosis, and disordered eating is known as the female athlete triad. Any sensible floor has to differ by sex.

08. Subcutaneous Versus Visceral Fat

Body fat percentage tells you the total amount of fat, but not where it sits. From a health-risk standpoint, visceral fat matters more than subcutaneous fat. Visceral fat releases fatty acids into the portal vein, which feeds directly into the liver, so it more readily affects blood lipids and glucose regulation. Two people with identical percentages can face different risks if one carries it concentrated around the abdomen.

09. Why Protecting Lean Mass Matters

In weight loss, what you lose matters as much as how much. Rapid dieting strips muscle along with fat, pulling lean body mass down with it. Since lean mass drives most of your basal metabolic rate, losing it lowers the energy you burn at rest. That is one reason the same diet starts producing plateaus and rebound weight gain. Recording body weight and lean body mass side by side reveals whether the loss was actually fat.

10. Athletes Differ by Sport

Lower is not automatically better; each sport has its own useful range. Marathon runners stay lean because lighter is faster, while in open-water swimming and sumo, fat contributes buoyancy and mass. Sports demanding strength relative to body weight, such as gymnastics and figure skating, push the figure down; sports built on absorbing collisions, such as American football linemen, push it up. Whether a number is good depends on what the body is for.