Lean Body Mass Calculator

Calculate your lean body mass and body fat mass using the Boer formula. Free, instant, no signup.

How to use the Lean Body Mass Calculator

  1. Enter your values. Fill in the fields with your numbers.
  2. Calculate. Press Calculate to run the lean body mass calculator.
  3. Use the result. Copy the result or try a related tool next.

Why use our Lean Body Mass Calculator

Instant results. Enter your figures and the lean body mass calculator returns an answer in seconds.
Free & private. Runs in your browser — no signup, and nothing is sent to a server.
Accurate. Uses standard formulas so you can rely on the numbers.

Free to use — premium coming soon

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About the Lean Body Mass Calculator

The Lean Body Mass Calculator estimates how much of your total weight is made up of everything that is not fat: muscle, bone, organs, blood, skin, and the water held inside them. Lean body mass (LBM) typically accounts for roughly 60 to 90 percent of total body weight, with the rest being fat. Knowing your LBM gives you a far more useful picture of your body than the bathroom scale alone, because two people at the same weight can carry very different amounts of muscle and fat. This tool turns a few simple measurements into a fast, sex-specific estimate you can track over time.

Reach for this calculator when the number on the scale is not telling the whole story. It is especially handy during a fat-loss phase, where the goal is to lose fat while protecting muscle: if your weight drops but your estimated LBM holds steady, you are likely losing the right kind of weight. Strength athletes use it to confirm that bulking gains are lean rather than mostly fat. It also feeds into nutrition planning, since protein targets are often set per kilogram of lean mass (commonly cited at roughly 1.6 to 2.2 g/kg for active people) rather than per kilogram of total body weight.

Under the hood, this calculator uses the Boer formula, one of the most widely cited height and weight equations for estimating LBM. For men it computes LBM (kg) = 0.407 x weight(kg) + 0.267 x height(cm) - 19.2, and for women LBM (kg) = 0.252 x weight(kg) + 0.473 x height(cm) - 48.3. Because the equation is sex-specific, choosing the wrong option will skew the result, so enter your details carefully. If you already know your body-fat percentage from a more direct measurement, the more accurate route is LBM = weight x (1 - bodyfat% / 100).

Treat the output as a solid estimate, not a clinical measurement. Height and weight formulas like Boer were derived from study populations and can over- or under-estimate true LBM by several kilograms compared with a DEXA scan, particularly for people at the extremes of muscularity or body fat. For research-grade precision, DEXA, hydrostatic weighing, or air-displacement methods are the references. On privacy: every calculation here runs entirely in your browser. Your height, weight, age, and sex are never uploaded, stored, or shared, so you can check your numbers as often as you like without leaving a trace.

Frequently asked questions

What formula does this calculator use?

It uses the Boer formula, a widely cited height and weight equation. For men, LBM (kg) = 0.407 x weight(kg) + 0.267 x height(cm) - 19.2; for women, LBM (kg) = 0.252 x weight(kg) + 0.473 x height(cm) - 48.3. If you know your body-fat percentage, LBM = weight x (1 - bodyfat%/100) is more accurate.

How accurate is a lean body mass estimate from height and weight?

It is a close estimate, not an exact figure. Formulas like Boer can differ from a DEXA scan by several kilograms (studies note roughly plus or minus 3.5 to 8.6 kg), with the largest errors for very muscular or very high body-fat individuals. For precise results, use DEXA, hydrostatic weighing, or air-displacement plethysmography.

Is lean body mass the same as muscle mass?

No. Muscle is the largest part of lean body mass, but LBM also includes bone, organs, blood, skin, and body water. Skeletal muscle alone is typically a smaller subset of your total lean mass, so a rising LBM reflects more than just muscle gain.

Why does the calculator ask for my sex?

Men and women carry different proportions of muscle, bone, and essential fat, so the Boer formula uses separate equations for each. Selecting the wrong sex applies the wrong coefficients and constant, which can shift your result by several kilograms.

What is a healthy lean body mass percentage?

Lean mass commonly makes up about 68 to 90 percent of total body weight, with the remainder being fat. There is no single ideal number, since it varies with sex, age, height, and training. Tracking the trend over time is more useful than chasing one target value.

From our blog

How the Army One-Site Tape Test Works and How to Estimate Your Score

By the Super Simple Digital Tools Team · Updated June 2026

The Army Body Composition Program exists to keep soldiers within a healthy body composition range, and in 2024 it moved to a simpler way of measuring it. Where the old method required taping multiple sites and applying log-based equations, the current one-site test asks for just your body weight and the circumference of your abdomen. That change makes the assessment faster, more consistent between graders, and easy to replicate at home, which is exactly what this calculator does.

The process starts with a screening, not a tape. Each soldier is first checked against a height and weight table for their age and sex. If you fall at or under the maximum screening weight for your height, you meet the standard and no tape test is needed. Only when you exceed that weight does the abdominal measurement come into play to determine your body fat percentage, so knowing your number in advance tells you whether the tape will ever come out.

Taking the measurement correctly matters more than people expect. Use a flexible tape that does not stretch, remove belts and bulky clothing, and stand tall with feet about hip-width apart. Place the tape at the level of your navel, keep it horizontal all the way around, and snug it against the skin without compressing the tissue. Read it at the end of a relaxed breath out. Because a single reading can be off, the Army takes three and averages them to the nearest half inch.

Once you have weight and abdomen in hand, the formula does the rest. Men and women use different equations because body fat distributes differently, but both depend only on those two inputs. Plug your averaged abdomen measurement and current weight into the calculator and it returns an estimated percentage. The tool then compares that figure to the maximum allowed for your age group, giving you a clear pass or work-needed signal rather than just a raw number.

Treat the output as a planning tool. Trends matter more than any one reading: track your estimate every couple of weeks as you train, and you will see how abdominal measurement responds to changes in diet and conditioning. When an official assessment is on the calendar, measure under the same conditions each time so your home estimates stay comparable, and remember that your unit's graded result is the one that counts on the record.

  • Average three abdomen readings to the nearest half inch, just as a grader would, instead of trusting a single measurement.
  • Measure at the navel at the end of a relaxed exhale, and never suck in or push your stomach out.
  • Compare your weight to the height and weight screening table first; if you are under it, the tape test may not apply at all.
  • Re-check your estimate at the same time of day and in similar conditions so progress between sessions is genuinely comparable.

Read the full guide →

Tool by the Super Simple Digital Tools Team. Reviewed by our editorial team. Free to use, no signup required.

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