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Health & Body
Lean Body Mass Calculator — Boer Formula (LBM & Body Fat Mass)
See how much of your weight is muscle, bone and organs versus fat — in plain pounds
Your lean body mass (LBM) is everything your body is made of except fat: muscle, bone, organs, water and connective tissue. Subtract it from your scale weight and what's left is your body fat mass. Knowing the split matters more than the scale number alone — two people can weigh the same 180 lb yet have very different amounts of muscle and fat.
This calculator uses the Boer formula, one of the most widely cited equations for estimating LBM from just your sex, height and weight. The formula runs in metric, so we convert your pounds to kilograms and your feet-and-inches to centimeters behind the scenes, then convert the answer back to pounds for you.
The Boer formula: • Men: LBM (kg) = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2 • Women: LBM (kg) = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3
Worked example. A man who is 5 ft 10 in (70 in) and weighs 180 lb: 180 lb = 81.65 kg, and 70 in = 177.8 cm. LBM = 0.407 × 81.65 + 0.267 × 177.8 − 19.2 = 33.23 + 47.47 − 19.2 = 61.5 kg ≈ 135.6 lb. His body fat mass is 180 − 135.6 = 44.4 lb, or about 24.7% body fat.
The common mistake: confusing lean body mass with muscle mass. LBM includes muscle, but also bone, organs and roughly 5–6 lb of essential fat that lives inside the lean compartment in some models — so LBM is always larger than skeletal muscle alone. Another slip is using the wrong sex toggle; the men's and women's equations give noticeably different answers, so pick the one that matches your body.
The Boer formula is an estimate built on population averages. It can't see your actual muscle-to-bone ratio, your hydration, or where you carry fat, so a very lean athlete or a heavily-built lifter may sit outside the typical range. For a true reading you'd need a DEXA scan, hydrostatic weighing, or a Bod Pod.
Informational only — this is not medical advice. Use the number as a rough baseline to track changes over time, not as a diagnosis. For body-composition goals or health concerns, talk with a doctor or a registered dietitian.
📖 See also: Body Fat Percentage: How to Measure It at Home
Calculator
Fill in the fields and click "Calculate" for instant results.
📰 Formula
• Convert: weight(kg) = weight(lb) × 0.45359237 • Convert: height(cm) = (feet × 12 + inches) × 2.54 • Men: LBM(kg) = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2 • Women: LBM(kg) = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3 • Lean mass(lb) = LBM(kg) ÷ 0.45359237 • Body fat mass(lb) = total weight(lb) − lean mass(lb) • Body fat % = body fat mass ÷ total weight × 100
📰 Formula
• Convert: weight(kg) = weight(lb) × 0.45359237 • Convert: height(cm) = (feet × 12 + inches) × 2.54 • Men: LBM(kg) = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2 • Women: LBM(kg) = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3 • Lean mass(lb) = LBM(kg) ÷ 0.45359237 • Body fat mass(lb) = total weight(lb) − lean mass(lb) • Body fat % = body fat mass ÷ total weight × 100
🧪 Worked examples
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Example 2
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Example 3
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Example 4
⚠️ Common mistakes
- Treating lean body mass as pure muscle — LBM also includes bone, organs and water, so it's always larger.
- Selecting the wrong sex; the men's and women's Boer equations give different results.
- Entering height as inches only (e.g. 70) in the feet box instead of splitting 5 ft 10 in.
- Expecting clinical precision — Boer is a population estimate, not a DEXA-level measurement.
💡 Tips
- Track the trend, not a single reading — LBM holding steady while the scale drops means you're losing fat, not muscle.
- Many coaches set protein at about 0.7–1.0 g per pound of lean body mass; this gives you that base number.
- If you lift seriously or are very lean, treat the result as a floor — Boer tends to under- or over-shoot at the extremes.
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❓ Frequently asked questions
What is lean body mass?
Lean body mass is your total body weight minus your fat mass. It includes muscle, bone, organs, body water and connective tissue — everything that isn't stored fat.
Is lean body mass the same as muscle mass?
No. Muscle is part of your lean body mass, but LBM also counts bone, organs and water. Your skeletal muscle is always less than your total lean body mass.
What is the Boer formula?
It's a population-based equation that estimates LBM from sex, height and weight. Men: LBM = 0.407×kg + 0.267×cm − 19.2. Women: LBM = 0.252×kg + 0.473×cm − 48.3.
How accurate is this lean body mass calculator?
It's a solid ballpark for average adults, usually within a few pounds of a scan. Very muscular, very lean, or very heavy people can fall outside the range, since the formula only sees height, weight and sex.
How do I find my body fat mass and body fat percentage?
Body fat mass = total weight − lean body mass. Body fat percentage = fat mass ÷ total weight × 100. This calculator shows both automatically once you enter your numbers.
What is a healthy lean body mass percentage?
There's no single target — it depends on your goals and body type. Many active men sit around 80–88% lean (12–20% fat) and many active women around 72–82% lean (18–28% fat), but ranges vary widely.
Why do men and women use different formulas?
Women naturally carry more essential fat and have a different muscle-to-fat distribution, so the Boer equation uses separate coefficients for each sex to stay accurate.
Can I use lean body mass to set my protein intake?
Yes — scaling protein to LBM avoids over-counting stored fat. A common range is 0.7–1.0 grams of protein per pound of lean body mass, though needs vary by activity and goals.
Is a lean body mass estimate a substitute for a body scan?
No. For a precise reading, use DEXA, hydrostatic weighing or a Bod Pod. This formula is informational only and is not a medical diagnosis or treatment advice.