OneTaskBy Tim King · Updated
Lean Body Mass Calculator
Boer, James and Hume Formulas, Fat-Free Mass From Body Fat Percentage
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How the Lean Body Mass Calculator works
This lean body mass calculator estimates how much of your weight is everything except fat: muscle, bone, organs and water. It compares the Boer, James and Hume formulas from height and weight, or uses your body fat percentage directly if you know it, and adds your fat mass, fat-free mass index and what you would weigh at other body fat levels.
Lean body mass, or LBM, is the part of your body that burns most of your calories and does the work. It is used to dose some medicines and anaesthetics, set protein targets and track whether a diet is taking off fat or muscle. Two people at the same weight can differ in lean mass by 15 kg or more.
How the lean body mass calculator works
With a body fat percentage, the formula is simply LBM = weight × (1 − body fat ÷ 100). Without one, the Boer formula estimates it from height and weight: for men LBM = 0.407 × weight + 0.267 × height − 19.2, and for women 0.252 × weight + 0.473 × height − 48.3, in kg and cm. James and Hume are older equations shown for comparison. Fat-free mass index is LBM divided by height in metres squared.
First example. A man 180 cm tall weighing 80 kg has a Boer lean body mass of 0.407 × 80 + 0.267 × 180 − 19.2 = 61.4 kg, so about 18.6 kg of fat and an FFMI of 19.
Second example. A woman weighing 65 kg with 28% body fat has a lean body mass of 65 × 0.72 = 46.8 kg and 18.2 kg of fat.
How many kilograms of muscle can I gain? A fat-free mass index of about 25 is the natural limit for most men, and about 21 to 22 for women.
Estimated lean body mass in kg by weight for a 178 cm man and a 165 cm woman
| Body weight | Man, Boer | Man, Hume | Woman, Boer | Woman, Hume |
|---|---|---|---|---|
| 50 kg (110 lb) | 48.7 | 47.3 | 42.3 | 40.5 |
| 55 kg (121 lb) | 50.7 | 48.9 | 43.6 | 42.0 |
| 60 kg (132 lb) | 52.7 | 50.5 | 44.9 | 43.4 |
| 65 kg (143 lb) | 54.8 | 52.2 | 46.1 | 44.9 |
| 70 kg (154 lb) | 56.8 | 53.8 | 47.4 | 46.4 |
| 75 kg (165 lb) | 58.9 | 55.5 | 48.6 | 47.9 |
| 80 kg (176 lb) | 60.9 | 57.1 | 49.9 | 49.4 |
| 85 kg (187 lb) | 62.9 | 58.7 | 51.2 | 50.8 |
| 90 kg (198 lb) | 65.0 | 60.4 | 52.4 | 52.3 |
| 95 kg (209 lb) | 67.0 | 62.0 | 53.7 | 53.8 |
| 100 kg (220 lb) | 69.0 | 63.7 | 54.9 | 55.3 |
| 105 kg (231 lb) | 71.1 | 65.3 | 56.2 | 56.7 |
| 110 kg (243 lb) | 73.1 | 67.0 | 57.5 | 58.2 |
| 115 kg (254 lb) | 75.1 | 68.6 | 58.7 | 59.7 |
| 120 kg (265 lb) | 77.2 | 70.2 | 60.0 | 61.2 |
| 125 kg (276 lb) | 79.2 | 71.9 | 61.2 | 62.7 |
| 130 kg (287 lb) | 81.2 | 73.5 | 62.5 | 64.1 |
| 135 kg (298 lb) | 83.3 | 75.2 | 63.8 | 65.6 |
| 140 kg (309 lb) | 85.3 | 76.8 | 65.0 | 67.1 |
| 145 kg (320 lb) | 87.3 | 78.4 | 66.3 | 68.6 |
Tips and pitfalls
- Use body fat % when you have it. A measured body fat figure, even from a tape measure, beats the height-and-weight formulas, which assume average build.
- Formulas fail at the extremes. For very light or very heavy people the Boer and Hume equations drift, and the James formula can even fall as weight rises.
- Lean mass includes water. Day-to-day swings in hydration and stored carbohydrate shift lean mass by a kilogram or more, so compare readings taken under the same conditions.
- FFMI rewards muscle. Above about 20 for men or 17 for women shows more muscle than average.
FAQ
What is a good lean body mass?
There is no single target, because lean mass scales with height and frame. A more useful measure is fat-free mass index: an FFMI of 18 to 20 is typical for men and 15 to 17 for women, while trained lifters often reach 22 or more.
Is lean body mass the same as muscle mass?
No. Lean body mass includes everything that is not fat, so bones, organs, skin, blood and water are counted along with skeletal muscle. Skeletal muscle usually makes up only about 40 to 50% of lean mass in healthy adults.
Which lean body mass formula is most accurate?
For adults of average build, Boer usually lands closest to measured values and is the one most often used in medicine. Hume is similar. The James formula works for average weights but breaks down for very heavy people, so it is shown for comparison only.
Why does lean body mass matter for dosing drugs?
Many drugs spread mainly into lean tissue rather than fat, so dosing by total body weight can overdose people with a lot of body fat. Anaesthetists and oncologists often use lean body mass, usually from the Boer or James formula, to set safer doses.
How can I increase my lean body mass?
Lift weights or do other resistance training two to four times a week, eat about 1.6 g of protein per kilogram of body weight daily and get enough sleep. Beginners can often add 0.5 to 1 kg of lean mass a month in their first year of training.
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