瘦体重计算器

使用 Boer、James 与 Hume 公式估算去脂体重。

Lean body mass

Sex

Height

Weight

Boer

61.4kg

James

62.7kg

Hume

57.8kg

What lean body mass is

Lean body mass is your total body weight minus your stored fat. Everything else — skeletal muscle, smooth muscle, organs, bone, blood, lymph, the water inside all of it — counts as “lean.”

Why it matters:

Metabolism scales with LBM. Two people with identical body weights but different LBM will have different basal metabolic rates. The Katch-McArdle BMR formula uses LBM directly because it’s a stronger metabolic predictor than total weight.
Strength and performance scale with LBM. More specifically, with the muscle-mass subset of LBM. A larger LBM is a hard ceiling on how strong you can be.
Fat loss potential scales with LBM. A heavier-LBM person can run a larger absolute deficit while preserving muscle. A lower-LBM person needs to be more careful with deficit size.
Protein needs scale with LBM. Setting protein on g/kg LBM is more accurate than g/kg total weight, especially for very lean or very obese individuals.

The three formulas

All three are predictive equations from height and weight. They were each fit to different reference data sets, which is why they disagree slightly.

Boer (1984)

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 most-cited modern LBM formula. Boer was developed for use in pharmacology when dosing decisions depend on lean tissue. It is our default and tracks DXA-measured LBM closely for healthy adults.

James (1976)

Men:   LBM = 1.10 × weight(kg) − 128 × (weight(kg)² / height(cm)²)
Women: LBM = 1.07 × weight(kg) − 148 × (weight(kg)² / height(cm)²)

The James formula is older and uses a different functional form — it scales lean mass with weight directly and subtracts a quadratic body-mass-index-like correction. Tends to slightly underestimate at high BMIs.

Hume (1966)

Men:   LBM = 0.32810 × weight(kg) + 0.33929 × height(cm) − 29.5336
Women: LBM = 0.29569 × weight(kg) + 0.41813 × height(cm) − 43.2933

The oldest of the three. Originally developed from cadaver and balance studies. Tends to slightly underestimate LBM for women at the lighter weight end.

A worked example

A 30-year-old man, 80 kg, 180 cm:

Boer: 0.407 × 80 + 0.267 × 180 − 19.2 = 32.56 + 48.06 − 19.2 = 61.4 kg
James: 1.10 × 80 − 128 × (80² / 180²) = 88 − 128 × 0.1975 = 88 − 25.28 = 62.7 kg
Hume: 0.32810 × 80 + 0.33929 × 180 − 29.5336 = 26.25 + 61.07 − 29.53 = 57.8 kg
Average: 60.6 kg.

If this same man’s body fat is 20% (measured by tape or DXA), his measured LBM is 80 × 0.80 = 64 kg — slightly higher than all three formulas, which is typical for a moderately trained lifter.

A 28-year-old woman, 65 kg, 168 cm:

Boer: 0.252 × 65 + 0.473 × 168 − 48.3 = 16.38 + 79.46 − 48.3 = 47.5 kg
James: 1.07 × 65 − 148 × (65² / 168²) = 69.55 − 148 × 0.1497 = 69.55 − 22.16 = 47.4 kg
Hume: 0.29569 × 65 + 0.41813 × 168 − 43.2933 = 19.22 + 70.25 − 43.29 = 46.2 kg
Average: 47.0 kg.

Excellent agreement here — all three within 1.3 kg. This is typical for adults inside the formulas’ validation ranges (BMI 18–30 or so).

How to use this calculator

Toggle metric or imperial.
Enter age, sex, weight, and height.
The calculator returns all three formulas plus the average.
If you know your body fat percentage (from the body fat calculator, DXA, or skinfolds), the simple weight × (1 − BF/100) calculation is more accurate — use that instead.

When to use LBM vs. total body weight

Goal	Use total weight	Use LBM
Calorie target via TDEE	✓	(only if very obese)
Protein target	(acceptable)	✓ (more accurate)
Strength-to-weight comparison	✓	(rarely useful)
BMR via Katch-McArdle	—	✓
Tracking body recomposition	—	✓

Tracking LBM over time

LBM is the cleanest signal that body recomposition is working:

Cutting: LBM stable (±1 kg), total weight down → ideal scenario. You’re losing fat, keeping muscle.
Cutting: LBM down by more than 1 kg over 4 weeks → deficit is too aggressive, protein too low, or training stimulus has dropped. Adjust.
Bulking: LBM up, total weight up → working. Aim for at least 50% of weight gain to be LBM if you’re past your first year of training.
Bulking: LBM flat, total weight up → most of the gain is fat. Drop the surplus by 100–150 kcal.

To track LBM accurately over time, use the same method each time (same calculator, same body fat method, same time of day). Method-to-method noise is larger than the actual changes you’re trying to detect.

When the formulas miss

Very high body fat. James and Boer both tend to overestimate LBM for individuals over BMI 35.
Highly muscular athletes. All three underestimate by 3–8 kg for trained powerlifters, bodybuilders, and rugby forwards. Use a body-fat-based calculation in that case.
Older adults. Sarcopenia (age-related lean-mass loss) isn’t captured by the formulas, which use the same coefficients regardless of age.
Edema or significant fluid retention. “Lean” mass includes water, so retained fluid inflates the estimate. Re-measure once fluid status is normal.

常见问题

What is lean body mass exactly?

Lean body mass (LBM), also called fat-free mass, is everything in your body that **isn't** stored body fat — muscle, bone, organs, water, connective tissue. It's the number that scales metabolism, drives strength performance, and determines how much fat you can lose without losing muscle.

How is LBM different from "muscle mass"?

Muscle is a *subset* of LBM. A typical adult's LBM is about 50% skeletal muscle plus 50% bone, organs, and water. When people say "I want to gain muscle", they specifically mean increasing skeletal muscle mass, but LBM is what most calculators and formulas can actually measure.

Which formula should I use?

For most adults, the three formulas agree within 2 kg, so the average is fine. **Boer** is generally the most cited and is what we recommend as the default. **Hume** tends to underestimate slightly for women; **James** is the oldest and is included for comparison. If you have a body-fat percentage measurement, the simple `weight × (1 − BF%)` calculation is the most accurate.

Why does the calculator need both height and weight?

Height-and-weight formulas use both because LBM scales with both body size dimensions. A 90 kg, 200 cm individual has different LBM than a 90 kg, 165 cm individual at the same body fat percentage — the formulas implicitly account for that.

Can I use LBM to set a protein target?

Yes — and it's actually more accurate than using total body weight. Targeting **2.2 g per kg of LBM** is equivalent to about 1.6–1.8 g per kg of total weight for a typical lifter. For very obese individuals, body-weight-based protein targets overshoot; LBM-based targets are more sensible.

How does LBM change during a cut or bulk?

A well-run cut should preserve LBM (or nearly so) and lose fat. A well-run bulk should add LBM (along with some fat). The change in LBM over 4–8 weeks is the cleanest signal of whether your training and nutrition are working — much cleaner than total body weight.