How accurate is the LBM calculator without body fat percentage?

When using the Boer formula (without body fat % input), accuracy is moderate — roughly ±3–5 kg compared to DEXA scan measurements. The formula works best for adults with average body composition. If you are significantly over- or under-weight, or have very high muscle mass, the estimate may be less accurate. Entering your measured body fat percentage (from a skinfold test, BIA scale, or our Body Fat Calculator) gives a more precise result.

Lean Body Mass Calculator

Q: What is lean body mass?

Lean body mass (LBM) — also called fat-free mass — is the total weight of everything in your body except fat. This includes muscle, bone, organs, skin, and water. LBM is a key metric for tracking fitness progress because it distinguishes whether weight changes are due to fat loss, muscle gain, or both. Most fitness goals — including strength, endurance, and metabolic health — are more closely tied to LBM than to total body weight.

Q: What is the Boer formula for lean body mass?

The Boer formula (1984) estimates lean body mass from weight and height: for men, LBM = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2; for women, LBM = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3. It is widely used in clinical pharmacology for medication dosing and is considered one of the more accurate anthropometric LBM formulas, particularly for adults with average body composition.

Q: Why does lean body mass matter for protein intake?

Protein recommendations for active individuals are based on lean body mass rather than total body weight because fat tissue has minimal protein turnover. Research supports 1.6–2.2 g of protein per kilogram of LBM per day for muscle maintenance and growth. This means a 90 kg person with 30% body fat (LBM ≈ 63 kg) needs approximately 100–140 g of protein per day — less than if the calculation were based on total body weight.

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

Lean body mass includes all non-fat tissue: muscle, bone, organs, skin, and body water. Muscle mass is a subset of LBM — specifically the skeletal muscle tissue used for movement. Muscle typically represents about 35–45% of total body weight in active adults. You cannot calculate muscle mass alone without advanced methods like DEXA or MRI, but LBM is a useful proxy for tracking muscle-building progress over time.

Calculate your lean body mass (fat-free mass) and fat mass. Use the Boer formula default or enter your known body fat percentage for a more precise result.

Formula: Boer (1984) — estimates LBM from weight and height. If you enter your body fat percentage below, that value overrides the Boer formula for greater precision.

Sex

Male

Female

Weight

Height

Body Fat % (optional — overrides Boer formula)

Use the Body Fat Calculator to find your body fat %.

What Is Lean Body Mass?

Lean body mass (LBM) — also called fat-free mass (FFM) — is the total weight of your body minus all fat tissue. It includes muscle, bone, connective tissue, organs, skin, and water. For a 70 kg man with 20% body fat, LBM would be 56 kg, with the remaining 14 kg being fat.

LBM is one of the most meaningful metrics in fitness and health. It underpins your resting metabolic rate (muscle is metabolically active), determines your protein requirements, and is the core of what changes when you "get lean." Tracking LBM over time is far more informative than tracking scale weight alone.

How the Boer Formula Works

This calculator uses the Boer formula (1984), which estimates LBM from body weight and height. The formulas are:

Men: LBM = 0.407 × weight (kg) + 0.267 × height (cm) − 19.2
Women: LBM = 0.252 × weight (kg) + 0.473 × height (cm) − 48.3

The Boer formula is widely used in clinical pharmacology (for calculating drug doses based on LBM) and is considered one of the more accurate anthropometric formulas for adults with average body composition. Its typical accuracy is ±3–5 kg compared to gold-standard DEXA scanning.

If you enter your measured body fat percentage, the calculator uses the direct method instead: LBM = weight × (1 − body fat% ÷ 100). This is more precise because it incorporates your actual body composition data.

Lean Body Mass and Protein Requirements

Protein recommendations for active individuals should be calculated from LBM, not total weight. Fat tissue requires very little protein — so using total weight overestimates protein needs for overweight individuals and may underestimate them for very lean athletes.

Goal	Protein per kg LBM	Example (60 kg LBM)
Maintenance	1.4–1.6 g/kg	84–96 g/day
Muscle building	1.6–2.2 g/kg	96–132 g/day
Fat loss (preserve muscle)	2.0–2.4 g/kg	120–144 g/day

Use the Protein Calculator to calculate your personalised protein targets, and the TDEE Calculator for your daily calorie needs.

Tracking Body Composition Progress

The most common mistake in tracking fitness progress is focusing only on the scale. Your LBM can increase while your fat decreases — leading to no change (or even an increase) in total weight, even when you are making excellent progress. This is why tracking LBM and fat mass separately gives a far more accurate picture.

Re-test every 4–6 weeks using the same method and conditions (morning, before eating, same time of day). Small week-to-week fluctuations are normal; look for consistent trends over a 6–12 week period. For a comprehensive view of your body composition, read the Body Composition Guide.

Scientific References: Boer P. (1984). Estimated lean body mass as an index for normalization of body fluid volumes in humans. American Journal of Physiology. 247(4 Pt 2):F632–636. — Morton RW, et al. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine. 52(6):376–384.

Medical Disclaimer: The results from this calculator are for informational and educational purposes only. LBM estimates are based on population-level formulas and may not reflect your individual body composition. Do not use these results as a substitute for clinical assessment or professional medical advice. Consult a qualified healthcare provider or registered dietitian before making significant changes to your nutrition or training programme.

Last reviewed: August 2026 · Boer formula: Boer P. (1984). Am J Physiol.

Frequently Asked Questions

What is lean body mass?

Lean body mass (LBM) is the total weight of everything in your body except fat — muscle, bone, organs, skin, and water. It is the metabolically active portion of your body that drives your resting calorie burn and determines your protein needs. Tracking LBM over time is more informative than tracking total body weight because it separates fat loss from muscle gain.

What is the Boer formula for lean body mass?

The Boer formula (1984) estimates LBM from weight and height: males = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2; females = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3. It is widely used in clinical pharmacology and is one of the more accurate anthropometric LBM formulas for adults with average body composition, with accuracy of approximately ±3–5 kg vs DEXA.

How accurate is this LBM calculator?

Using the Boer formula alone, accuracy is approximately ±3–5 kg compared to DEXA scanning. The formula works best for adults with average body composition. Entering your measured body fat % (from a skinfold test, BIA scale, or the Body Fat Calculator) overrides the formula and gives a more precise result based on your actual composition.

Why does lean body mass matter for protein intake?

Protein requirements are driven by muscle tissue, not fat. Using LBM to calculate protein targets gives a more accurate result — especially for people who are significantly over- or under-weight. Research supports 1.6–2.2 g of protein per kg of LBM per day for muscle maintenance and growth during resistance training.

How can I increase my lean body mass?

Lean body mass increases primarily through resistance training and adequate protein intake. Prioritise compound lifts (squats, deadlifts, rows, bench press) with progressive overload. Eat 1.6–2.2 g of protein per kg of LBM per day, ensure sufficient sleep (7–9 hours), and maintain a small calorie surplus (200–300 kcal above maintenance) if muscle gain is the goal.

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

Lean body mass includes all non-fat tissue — muscle, bone, organs, skin, and water. Muscle mass (specifically skeletal muscle) is a subset of LBM. Skeletal muscle typically represents about 35–45% of total body weight in active adults. You cannot isolate muscle mass from LBM without advanced testing (DEXA or MRI), but LBM is a practical proxy for tracking muscle-building progress over time.