Ultimate Lean Body Mass Calculator: Boer, James, Hume & Peters Formulas
Lean Body Mass Calculator: Estimate Your LBM Using 4 Proven Formulas
Updated February 2026
Lean body mass (LBM) is your total body weight minus all stored fat—essentially what you'd weigh if you had zero body fat. It includes muscle, bones, organs, water, and essential fat. Use the calculator below to estimate your LBM instantly using four clinically validated formulas, then learn how to apply your results to nutrition, training, and health goals.
What Is Lean Body Mass?
Lean body mass represents everything in your body that isn't storage fat: skeletal muscle, organs, bones, blood, skin, and connective tissue. It also includes essential fat—the small amount your body needs for basic cellular functions (roughly 3% of body weight in men, 10–12% in women).
Understanding your LBM helps you:
- Set precise protein targets – Most recommendations are based on lean mass, not total weight
- Track real progress – Know whether scale changes come from muscle gain, fat loss, or both
- Calculate accurate calorie needs – Lean tissue drives your metabolism
- Inform medical dosing – Some medications are prescribed based on lean body weight
Quick tip: While these formulas provide useful estimates, a DEXA scan measures your actual lean mass directly—no guesswork required.
How the LBM Formulas Work
Each formula below estimates lean body mass using height and weight, with sex-specific coefficients. The calculator displays results from all four so you can compare.
| Formula | Men | Women | Original Purpose |
|---|---|---|---|
| Boer (1984) | 0.407 × W + 0.267 × H − 19.2 | 0.252 × W + 0.473 × H − 48.3 | Normalize body fluid volumes for drug dosing (Boer 1984) |
| James (1976) | 1.10 × W − 128 × (W/H)² | 1.07 × W − 148 × (W/H)² | Body-size descriptor in obesity research (James 1976) |
| Hume (1966) | 0.32810 × W + 0.33929 × H − 29.5336 | 0.29569 × W + 0.41813 × H − 43.2933 | Creatinine-clearance calculations (Hume 1966) |
| Peters (2011) | 3.8 × 0.0215 × W^0.6469 × H^0.7236 | Same (sex-independent) | Pediatric drug dosing for children ≤14 years (Peters 2011) |
W = weight in kg; H = height in cm (James uses meters for the squared ratio)
The calculator handles all unit conversions automatically—enter your measurements in pounds/inches or kg/cm, and it does the math.
Why Do Formulas Give Different Results?
- Different study populations – Hume's data came from adults with kidney disease; Peters studied children; Boer focused on healthy adults.
- Different mathematical approaches – Boer and Hume use linear equations; James introduces a squared weight-to-height ratio that behaves differently at extreme body sizes.
- Different validation methods – Sample sizes, regression techniques, and reference methods varied across studies.
For most healthy adults, Boer tends to be the most widely used clinically. However, if you want true precision, a DEXA body composition scan gives you a direct measurement rather than an estimate.
How to Calculate LBM If You Know Your Body Fat Percentage
If you already have an accurate body-fat reading (from a DEXA scan, for example), you can calculate LBM directly:
LBM = Total Body Weight × (1 − Body Fat %)
Example: A 180 lb person at 18% body fat:
LBM = 180 × (1 − 0.18) = 180 × 0.82 = 147.6 lb
This method is more accurate than height-weight formulas when you have reliable body-fat data. Learn more in our guide to body composition vs. weight.
Methods for Measuring Lean Body Mass
1. DEXA (Dual-Energy X-Ray Absorptiometry) — Gold Standard
- Accuracy: ± 1% error rate (systematic review)
- What it measures: Lean mass, fat mass, bone density, and visceral fat in one 10-minute scan
- Radiation: About the same as eating four bananas—see our radiation explainer
DEXA is the benchmark method used in research and clinical practice. Compare DEXA to other methods or find a scan near you.
2. Bioelectrical Impedance Analysis (BIA)
- Quick and affordable (many smart scales use BIA)
- Accuracy concern: Can over- or under-estimate LBM by ± 8–19 lb (± 3.5–8.6 kg) compared with DEXA (Nature 2022)
- Results vary with hydration, meal timing, and skin temperature
3. Hydrostatic (Underwater) Weighing
- Accurate when performed correctly
- Requires full submersion and complete exhalation
- Less accessible and uncomfortable for many people
4. Skinfold Calipers
- Inexpensive and portable
- Accuracy depends heavily on technician skill—typical error is ± 3–5% body fat (NSCA review)
What to Do With Your Lean Body Mass Number
Set Protein and Calorie Targets
Protein recommendations are often expressed per pound of lean mass, not total body weight. A common evidence-based starting point is 0.7–1.0 g of protein per pound of LBM (ISSN position stand).
| Your LBM | Daily Protein Target |
|---|---|
| 120 lb | 84–120 g |
| 140 lb | 98–140 g |
| 160 lb | 112–160 g |
| 180 lb | 126–180 g |
For detailed guidance, see The Protein Primer or learn how much protein prevents muscle loss.
Your lean mass also drives your Basal Metabolic Rate (BMR)—more muscle means a higher resting metabolism. Use your LBM in a BMR or TDEE calculator for more accurate calorie targets than weight-based formulas provide.
Design Your Training Program
Muscle growth (hypertrophy) responds to training volume. Evidence-based guidelines recommend at least 10 weekly sets per muscle group to maximize gains (Schoenfeld 2016).
Knowing your starting lean mass helps you:
- Set realistic muscle-gain expectations (most natural lifters can add 1–2 lb of muscle per month when new to training)
- Track whether your program is actually building muscle or just changing the scale
- Identify muscle imbalances between limbs (DEXA shows left vs. right lean mass)
For workout guidance, see our body composition exercises guide.
Clinical Applications (Important Disclaimer)
Certain medications—especially anesthetics, chemotherapy agents, and contrast dyes—are dosed based on lean or adjusted body weight. While the formulas above are clinically validated, only licensed healthcare providers should use them for medical dosing decisions.
⚠️ This article provides educational information and is not a substitute for professional medical advice. Always consult your physician or pharmacist before adjusting any medication.
Track Your Progress Over Time
Online calculators give you a snapshot, but body recomposition is a journey. Periodic DEXA scans provide a verified benchmark so you can:
- Confirm whether scale changes are muscle, fat, or water
- See regional changes (are your legs gaining muscle even if arms aren't?)
- Monitor visceral fat for metabolic health
- Validate which formula tracks closest to your actual LBM
Most people see meaningful composition changes in 8–12 weeks of consistent training and nutrition. Scanning every 2–3 months lets you catch what's working—and what isn't—before you've wasted months on an ineffective approach.
Ready to see your real numbers? Book a DEXA scan and turn estimates into verified data.
Frequently Asked Questions
What's the difference between lean body mass, fat-free mass, and BodySpec's "lean mass"?
These terms are related but not identical:
| Term | What It Includes | What It Excludes |
|---|---|---|
| Fat-Free Mass (FFM) | Muscle, bone, organs, water | All body fat (including essential fat) |
| Formula-based LBM (this calculator) | FFM + essential fat | Storage/adipose fat only |
| BodySpec DEXA "Lean Mass" | Muscle, organs, water (lean soft tissue) | Bone mineral content AND all fat |
Because BodySpec's lean-mass figure excludes bone, while formula-based LBM includes bone and essential fat, your formula result will typically be higher than your DEXA lean mass by roughly 6–10%.
For a deeper dive, see What Is Lean Body Mass? and interpreting DEXA results.
How do I calculate lean body mass manually?
If you know your body-fat percentage:
LBM = Weight × (1 − Body Fat %)
If you only know height and weight (Boer formula for adults):
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
Are these formulas accurate for athletes or very muscular people?
Not perfectly. Height-weight formulas assume average body composition. Very muscular individuals may have their LBM underestimated because the equations don't account for above-average muscle mass. If you're a serious athlete or bodybuilder, a DEXA scan is strongly recommended for accurate measurement.
What is a "healthy" lean body mass?
Context matters significantly. LBM varies by sex, age, height, and fitness level. As a rough benchmark:
- Men: LBM typically ranges from 75–90% of total body weight
- Women: LBM typically ranges from 68–85% of total body weight
A 180 lb man at 15% body fat has 153 lb LBM—above average for sedentary adults but common for recreational lifters. For age- and sex-specific reference ranges, see What Is Lean Body Mass?.
How do I convert between pounds/kilograms and inches/centimeters?
- 1 kg = 2.205 lb (divide pounds by 2.205 to get kg)
- 1 inch = 2.54 cm (multiply inches by 2.54 to get cm)
The calculator widget includes unit toggles so you can enter data in your preferred system.
Can I increase my lean body mass?
Yes. The primary drivers are:
- Resistance training – Progressive overload builds muscle (training guide)
- Adequate protein – 0.7–1.0 g per pound of LBM supports muscle protein synthesis (protein primer)
- Caloric balance – A slight surplus supports muscle gain; a moderate deficit with high protein preserves muscle during fat loss (body recomposition guide)
- Recovery – Sleep and stress management affect hormone levels that regulate muscle growth
Takeaway
Estimating lean body mass is step one; verifying it with a DEXA scan and acting on the data is where real progress happens.
Use this calculator to get a starting estimate, then:
- Book a DEXA scan to see your actual lean mass, fat mass, and visceral fat
- Set protein targets based on your verified LBM
- Track progress over time—not just on the scale, but in your actual body composition
Your lean mass is the foundation of your metabolism, your strength, and your long-term health. Start measuring what matters.
