How do I use lean body mass to calculate protein intake?

Research supports 1.6–2.2g of protein per kg of lean body mass (not total body weight) for muscle retention and growth. For example, if your LBM is 60kg, you need 96–132g of protein per day. Using LBM rather than total weight is more accurate because fat tissue requires little protein.

What is the difference between lean body mass and muscle mass?

Lean body mass includes all non-fat tissue: skeletal muscle, smooth muscle, water, bones, organs, and glycogen. Muscle mass refers specifically to skeletal muscle only. LBM is always higher than muscle mass alone. Skeletal muscle typically accounts for about 40–50% of total LBM.

Lean Body Mass Calculator

Q: What is lean body mass?

Lean body mass (LBM) is the weight of everything in your body except fat — including muscles, bones, organs, blood, and water. It is also called fat-free mass (FFM). Knowing your LBM helps calculate accurate protein intake targets, medication dosing, and athletic performance metrics.

Q: Which LBM formula is most accurate?

The Boer formula is widely considered the most accurate for adults of average build. The Janmahasatian formula is preferred for obese individuals. The average of multiple formulas gives the most reliable estimate for most people. DEXA scanning remains the gold standard.

Q: How can I increase my lean body mass?

The most effective ways to increase LBM are: progressive resistance training (3–5x per week), adequate protein intake (1.6–2.2g per kg LBM), a slight calorie surplus (200–300 kcal above maintenance), sufficient sleep (7–9 hours), and managing stress to reduce cortisol-driven muscle breakdown.

Calculate your lean body mass (LBM) using 5 validated scientific formulas — Boer, James, Hume, Peters, and Janmahasatian. Get your fat-free mass, body composition breakdown, daily protein targets, and personalised fitness insights.

5Scientific Formulas

LBMFat-Free Mass

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Our free lean body mass (LBM) calculator uses five scientifically validated formulas — Boer, James, Hume, Peters, and Janmahasatian — to give you the most accurate estimate of your fat-free mass. Knowing your lean body mass is essential for calculating precise daily protein targets (1.6–2.2g per kg LBM), setting realistic fat loss goals, adjusting calorie needs, and tracking muscle-building progress. Whether you are an athlete, bodybuilder, or just starting your fitness journey, this free LBM calculator works entirely in your browser — no sign-up, no API, completely private.

Lean Body Mass Calculator

Enter your measurements — select formulas — get instant LBM results with body composition breakdown

Measurement Units

Biological Sex

Height Stand straight, no shoes

Please enter a valid height (100–250 cm)

Weight Morning, before eating

Please enter a valid weight (30–300 kg)

Age

yrs

Please enter a valid age (15–100)

Body Fat % Optional

If known — enables exact fat/lean split. Use our Body Fat Calculator first.

Select Formulas to Include (select all for the best average estimate)

Boer (1984)

Best overall accuracy for adults. Widely used in clinical settings. ✦ Recommended

James (1976)

Classic formula, slightly overestimates in obese individuals. Good for average builds.

Hume (1966)

Uses weight and height. Simple and reliable for normal weight individuals.

Peters (2001)

Optimised for children and adolescents (2–14 yrs). Good for younger users.

Janmahasatian (2005)

Best for overweight and obese individuals. Corrects for excess fat mass.

Activity Level For nutrition targets

—

kg LBM

Lean Body Mass

Your Lean Body Mass

Your lean body mass includes muscle, bone, organs, blood, and water — everything except fat.

—

Lean Mass

—% of body weight

—

Fat Mass (Est.)

—% of body weight

—

Skeletal Muscle (Est.)

~45% of LBM

—

FFMI

Fat-Free Mass Index

Body Composition Breakdown

Muscle

Other

Fat

Skeletal Muscle

Other Lean Tissue

Fat Mass

Formula Comparison — All Selected Methods

Formula	LBM	Fat Mass (Est.)	LBM %	vs Average	Best for

Daily Protein Target

— g/day

Based on 1.6–2.2g protein per kg LBM. This range supports muscle retention and growth based on current sports nutrition research.

Estimated TDEE

— kcal/day

Total Daily Energy Expenditure estimated using Katch-McArdle formula based on lean mass and your activity level. More accurate than BMR-based methods.

Fat Loss Target Calories

— kcal/day

A 300–500 kcal daily deficit below your TDEE supports 0.3–0.5kg of fat loss per week while preserving lean muscle mass.

Muscle Gain Target Calories

— kcal/day

A modest 200–300 kcal surplus above your TDEE provides enough energy for muscle protein synthesis without excessive fat gain.

How to Use the Lean Body Mass Calculator

Enter Your Measurements

Input your height, weight, and age. Optionally add your known body fat percentage for a more precise body composition breakdown. Select your activity level for personalised nutrition targets.

Choose Your Formulas

Select one or more of the 5 validated formulas. For best results, use all 5 — the average gives the most reliable estimate. The Boer formula is most accurate for average adults; Janmahasatian is best for overweight individuals.

Read Your Results

Get your LBM, fat mass, skeletal muscle estimate, FFMI, body composition bar, daily protein targets, TDEE, calorie targets for fat loss or muscle gain, and personalised tips.

Frequently Asked Questions

What is lean body mass (LBM)?

Lean body mass is the weight of everything in your body except fat tissue — including skeletal muscle, smooth muscle, cardiac muscle, bones, organs, blood, skin, and water. It is also called fat-free mass (FFM). Knowing your LBM is more useful than total body weight for setting protein targets, calculating accurate calorie needs (via Katch-McArdle), and tracking body composition changes over time.

Which LBM formula is most accurate?

The Boer formula (1984) is considered the most accurate for adults of average body composition, as it was developed from a large dataset of adults. The Janmahasatian formula (2005) is preferred for overweight or obese individuals because it accounts for excess fat mass. Using the average of multiple formulas reduces individual formula bias and gives the most reliable result. DEXA scanning remains the clinical gold standard.

How do I use LBM to calculate protein intake?

Current sports nutrition research supports 1.6–2.2g of protein per kg of lean body mass per day for maintaining or building muscle. Using LBM rather than total body weight is more accurate because fat tissue has minimal protein turnover. For example: if your LBM is 65kg, you need approximately 104–143g of protein daily. Higher end of the range is recommended during calorie restriction or intense training.

What is FFMI and what are good scores?

FFMI (Fat-Free Mass Index) is calculated as LBM ÷ height² (m). It measures muscularity independent of height. For men: below 18 = below average, 18–20 = average, 20–22 = above average, 22–25 = very muscular, 25+ = exceptional (rare without performance enhancement). For women: 14–16 = average, 16–18 = above average, 18–20 = athletic, 20+ = exceptional.

How can I increase my lean body mass?

The most evidence-based approach: (1) Progressive resistance training 3–5x per week focusing on compound movements (squat, deadlift, press, row). (2) Eat 1.6–2.2g protein per kg LBM daily. (3) Maintain a modest calorie surplus of 200–300 kcal. (4) Sleep 7–9 hours — growth hormone peaks during deep sleep. (5) Manage stress to reduce cortisol-driven muscle catabolism. Expect 0.5–1kg of lean mass gain per month in optimal conditions.

Lean Body Mass Calculator

Lean Body Mass Calculator

Your Lean Body Mass

Daily Protein Target

Estimated TDEE

Fat Loss Target Calories

Muscle Gain Target Calories

How to Use the Lean Body Mass Calculator

Enter Your Measurements

Choose Your Formulas

Read Your Results

Frequently Asked Questions

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