Dr. David Taylor, MD, PhD · Last reviewed April 30, 2026

Lean Body Mass Calculator

Estimate your lean body mass with the Boer, James, and Hume formulas side-by-side — or use your own body-fat reading. Includes a Lean Mass Index chip versus population norms, a daily protein target, an optional fat-loss math panel, and a clinician-ready PDF log.

Lean Body Mass Calculator

Optional: target weight (for fat-loss math)
Lean body mass · Boer
135.6 lb
61.5 kg
Lean mass index
19.5 kg/m²
Average
Daily protein · active
109–135 g

Within the average range for your sex and age (Schutz 2002 norms). Lean mass index normalizes LBM to height, so it's a fairer comparison across body sizes than raw LBM.

Compare across methods

Educational reference only. Lean body mass formulas estimate within ±3–5 lbs of true LBM for most adults; outliers include very lean and very heavy populations, and all formulas underestimate LBM in trained athletes. For a precise measurement, a DEXA scan, Bod Pod, or hydrostatic weighing is the clinical standard. Talk to your clinician or a registered dietitian before starting a new nutrition or training program.

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How to use this calculator

  1. Enter your weight, height, sex, and age. Imperial or metric — toggle the unit on each input. Age affects the Lean Mass Index norms (the "Below / Average / Above average" chip), not the underlying LBM math.
  2. Pick a method. Boer is the clinical default and what we'd recommend for almost everyone. James and Hume are alternates that are useful for cross-checking — Hume tends to run lowest, James tends to run highest. Body fat % is the most accurate when you have a real reading from a DEXA scan, Bod Pod, or a smart scale.
  3. Read the three result panels. The big number is your LBM in your chosen method. The Lean Mass Index chip puts that number in context against the Schutz 2002 reference percentiles for your sex and age. The protein band turns LBM into a daily protein target (toggle Maintenance / Active / Cut depending on your goal).
  4. Optional: enter a target weight to see how much fat you'd need to lose to reach it while preserving lean mass. Useful for setting realistic cuts before a competition, a vacation, or a check-in with a coach.
  5. Save the reading to your log. Optional — entries stay on your device. After a few weeks, export the PDF for a coach, a trainer, or a clinician. Pair the trend with a daily reading from a smart bathroom scale to track lean mass and fat mass together.

Why this calculator is different from other lean body mass tools

Almost every lean body mass calculator online does one of three things: (a) ships a single formula and gives you one number, (b) requires a body-fat % reading you may not have, or (c) is a thin upsell for a supplement-store. None of them put the LBM number in context against population norms, none of them connect it to a daily protein target, and none of them save anything across visits. Here's what this tool does differently:

  • Four methods, side-by-side. Boer (default — what most clinicians use), James, Hume, and a body-fat-% method when you have a reading. The comparison row shows all four LBM values at once, so you can see how much they disagree (Hume runs ~5 lbs lower than Boer for many adults — that's a meaningful difference if you're setting a protein target).
  • Lean Mass Index against Schutz 2002 norms. Every result includes a colored chip — Below average / Average / Above average / Very high — based on percentile data from a 2,986-adult Caucasian reference cohort. Knowing your LMI is "above the 90th percentile for your sex and age" is more useful than a raw LBM number that doesn't account for height.
  • Daily protein target derived from LBM. Not from total body weight, not a one-size-fits-all "150 g protein/day" line. The Maintenance / Active / Cut bands map to ISSN Position Stand recommendations and Helms 2014 deficit research. Tap the band that matches your goal.
  • Fat-loss target panel. Enter a target weight and the tool calculates exactly how many pounds of fat you'd need to lose to get there — assuming you preserve all current LBM. This is the math most cuts get wrong.
  • Tracking log + clinician-ready PDF. Save dated readings across weeks or months, export a one-page chronological PDF with weight, LBM in both units, LMI, and method. Most calculators reset on every refresh.
  • Embeddable widget, free. Personal trainers, RDs, gym coaches, and nutrition educators can copy a one-line snippet and host the same interactive calculator on their site with attribution baked in.
  • Reviewed by a named clinician. Most LBM calculators are anonymous fitness widgets. This one is reviewed by Dr. David Taylor, MD, PhD, with cited sources for every formula.

How this calculator works (the math)

The four methods behind this tool come from peer-reviewed sources used in clinical practice for half a century. They differ in what they assume about how lean mass scales with weight and height, but for most adults they agree to within 5 pounds. Below are the canonical equations, in standard metric form.

Boer (1984) — clinical default

The Boer formula is the most-cited LBM equation in pharmacology and anesthesia, where LBM-based dosing matters for water-soluble drugs:

  • Men: LBM = 0.407 × W (kg) + 0.267 × H (cm) − 19.2
  • Women: LBM = 0.252 × W (kg) + 0.473 × H (cm) − 48.3

Source: Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in man. Am J Physiol 247: F632–F635 (1984).

James (1976) — alternate, runs slightly higher

The James equation comes from a UK obesity-research report and uses a quadratic correction for body composition. It tends to read 2–4 pounds higher than Boer at typical adult body sizes:

  • Men: LBM = 1.10 × W (kg) − 128 × (W/Hcm)²
  • Women: LBM = 1.07 × W (kg) − 148 × (W/Hcm)²

Hume (1966) — original, runs slightly lower

The Hume equation is the original simple-regression LBM formula and tends to read a few pounds lower than Boer:

  • Men: LBM = 0.32810 × W + 0.33929 × H − 29.5336
  • Women: LBM = 0.29569 × W + 0.41813 × H − 43.2933

Source: Hume R. Prediction of lean body mass from height and weight. J Clin Pathol 19(4): 389–391 (1966).

Body fat % — most accurate when you have the reading

If you've had a DEXA scan, a Bod Pod, hydrostatic weighing, or a recent smart-scale reading, the formula is exact rather than estimated:

LBM = body weight × (1 − body fat % / 100)

A man at 180 lb and 18% body fat has a lean body mass of 180 × 0.82 = 147.6 lb. Smart-scale body-fat readings drift, so use the average of 5–7 morning readings rather than a single number for the most reliable estimate.

Lean Mass Index (LMI)

Just like BMI normalizes weight to height², LMI normalizes lean body mass:

LMI (kg/m²) = LBM (kg) / [height (m)]²

Population norms are from Schutz et al. 2002 (Eur J Clin Nutr 56: 973–982), which published 10th, 50th, and 90th percentile LMI values for Caucasian adults aged 18–98 in a sample of 2,986 men and women. Knowing your LMI is "above the 90th percentile for women age 35–54" is far more interpretable than knowing it's 17.2 kg/m².

Three real-world examples

180-lb man at 18% body fat — formula vs scale-measured

Marcus is 5'10" (70 in), weighs 180 lb, and his smart scale reads 18% body fat. Using Boer, the tool estimates his LBM at 135.6 lb. Using the body-fat method with his scale reading, his LBM is 147.6 lb — a 12-pound spread. The truth is probably in between: home smart scales overestimate LBM by 5–10 lb in lean men, while Boer slightly underestimates LBM in men with higher-than-average muscle mass. For Marcus, splitting the difference (~141 lb LBM) and using that to set a protein target of ~140 g/day on training days is a reasonable middle ground.

Mid-life woman tracking lean mass during a cut

Eleanor is 5'4" (64 in), 145 lb, age 42. Her LBM by Boer is 99.6 lb and her LMI is 17.1 kg/m² — above the 90th percentile for women her age (Schutz 2002 reference: 17.0). She wants to drop 10 lb of fat for a wedding. The fat-loss panel shows: target weight 135 lb means 10 lb of fat to lose, ending at ~26% body fat. To preserve her current LBM through that cut, the tool suggests the Cut protein band at 100–120 g/day, plus continued resistance training. She logs her weight and LBM weekly through the cut and exports a PDF for her trainer at the 8-week mark — the trend (LBM steady, weight down) confirms she's losing fat, not muscle. Pair the daily weigh-in with the right body-fat scale and the trend gets even cleaner.

Athlete: when the formulas underestimate

James plays college rugby, is 6'1" (73 in), weighs 220 lb, and his recent DEXA puts his body fat at 12%. The body-fat method gives him 193.6 lb of LBM, while Boer reads 156.4 lb — a 37-pound underestimate. This is why every formula has the disclaimer "underestimates LBM in trained athletes": the regressions were built on average sedentary populations. For an athlete with a real DEXA reading, always use the body-fat method. For sport-nutrition planning, his daily protein target at 1.0 g/lb of LBM (DEXA) is ~194 g — roughly 50 g per meal across four meals. For recovery between sessions, an electrolyte powder and a massage gun for soft-tissue work both pull their weight at his training volume.

What a "good" LBM looks like (LMI percentile reference)

From Schutz et al. 2002 — 2,986 Caucasian adults, ages 18–98:

  • Men 18–34: 10th percentile 17.4, median 18.9, 90th percentile 20.4 kg/m²
  • Men 35–54: 10th 17.6, median 19.0, 90th 20.5 kg/m²
  • Men 55–74: 10th 16.8, median 18.2, 90th 19.7 kg/m²
  • Women 18–34: 10th 13.9, median 15.4, 90th 16.9 kg/m²
  • Women 35–54: 10th 14.1, median 15.5, 90th 17.0 kg/m²
  • Women 55–74: 10th 13.7, median 15.0, 90th 16.4 kg/m²

Two clinical interpretations matter most. First, declining LMI in older adults is a marker of sarcopenia — the age-related muscle loss that increases fall risk and reduces independence. Even if your weight is stable as you age, holding LMI steady requires resistance training plus enough protein to keep up with declining synthesis efficiency. Second, LMI below the 10th percentile in younger adults often correlates with under-eating, low resistance-training stimulus, or both — and the most reliable way to move it up is a structured strength program with progressive overload and adequate calories.

Daily protein targets, explained

The protein band on the result card uses three evidence-based ranges expressed per pound of LBM:

  • Maintenance — 0.7–0.8 g per lb LBM. Baseline turnover and general health for sedentary or lightly active adults. For a 140-lb LBM, that's 98–112 g/day.
  • Active / strength — 0.8–1.0 g per lb LBM. The range supported by the 2017 ISSN Position Stand on Protein and Exercise for adults doing resistance or endurance training. For a 140-lb LBM: 112–140 g/day.
  • Cut / lean preservation — 1.0–1.2 g per lb LBM. The range supported by Helms et al. 2014 for resistance-trained athletes in a calorie deficit. Higher protein in a cut preserves lean mass; lower protein during the same deficit costs LBM you spent years building.

These bands assume reasonably distributed intake across 3–5 meals — most muscle-protein synthesis research finds diminishing returns past ~40 g of protein in a single meal, so spread it out.

Frequently asked questions

Which formula is the most accurate?

For an adult of average build, Boer is the most widely cited and is what we'd default to. The body-fat-% method is more accurate if you have a reliable reading from DEXA, Bod Pod, or hydrostatic weighing. Smart-scale BIA readings drift and tend to overestimate LBM in lean people — average 5–7 morning readings if you're using one. None of the formulas are accurate for trained athletes (they all underestimate), pregnant women, or people with significant edema.

What is a good lean body mass for a woman?

It depends on your height, age, and activity level. The clearer answer comes from Lean Mass Index, not raw LBM. For women aged 35–54, the 50th percentile LMI is about 15.5 kg/m² — so a 5'4" (1.63 m) woman in that range would have an LMI×height² ≈ 41 kg = 90 lb of lean body mass. If you're above that for your height-age category you're above population average; if you're below, the most reliable lever is a structured strength program plus adequate protein.

How is lean body mass different from fat-free mass?

They're often used interchangeably and the difference is small. Lean body mass includes the small amount of essential fat inside organs (about 2–3% in men, 5–12% in women); fat-free mass excludes all fat. For practical purposes in a fitness or nutrition context, treat them as the same thing.

How do I calculate lean body mass in kg?

Switch the weight and height units to kg and cm using the toggles next to the inputs. The result then displays kilograms first with pounds as the secondary number. The underlying Boer / James / Hume formulas are all in metric internally — the imperial input is just converted before the math.

Can I embed this tool on my own site?

Yes — copy the embed snippet at the bottom of this page. The embedded version is a stripped-down variant designed for personal trainers, registered dietitians, gym websites, and nutrition educators. Required attribution is built in. There's no fee, no signup, no analytics attached.

Three categories cover most needs once tracking lean mass becomes a habit. Each links to the full review with current top picks, prices, and pros/cons:

  • Best Bathroom Scales — a smart scale with bioelectrical impedance gives you a daily body-fat reading you can plug straight into the body-fat-% method here. The trend is what matters; one reading can be off, seven readings averaged usually aren't.
  • Best Collagen Supplements — type I and III collagen support tendons, ligaments, and skin alongside whichever lean-mass goal you're pursuing. Especially relevant in midlife when connective-tissue turnover slows.
  • Best Electrolyte Powders — sodium and potassium replacement matters at training volumes high enough to move LBM upward. Plain water alone leaves performance on the table.

Sources & methodology

  • Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in man. Am J Physiol 247: F632–F635 (1984) — Boer formula.
  • James W. Research on obesity: a report of the DHSS/MRC group. HM Stationery Office, 1976 — James formula.
  • Hume R. Prediction of lean body mass from height and weight. J Clin Pathol 19(4): 389–391 (1966) — Hume formula.
  • Schutz Y, Kyle UU, Pichard C. Fat-free mass index and fat mass index percentiles in Caucasians aged 18-98 y. Eur J Clin Nutr 56: 973–982 (2002) — LMI population norms.
  • Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition Position Stand: Protein and exercise. JISSN 14:20 (2017) — protein band recommendations.
  • Helms ER, Zinn C, Rowlands DS, Brown SR. A systematic review of dietary protein during caloric restriction in resistance trained lean athletes. Int J Sport Nutr Exerc Metab 24(2): 127–138 (2014) — cut-band protein recommendation.

This tool is reviewed every 6 months for citation currency. About Dr. Taylor · Last reviewed April 30, 2026.

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Free for personal trainers, registered dietitians, gym websites, nutrition educators, and personal blogs. Required attribution is included in the snippet. No fee, no signup, no analytics attached to the embed. 

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