Bone Mass Calculator
Most people who search for their bone mass want one of two different numbers: a rough estimate of how much their skeleton weighs, or a way to tell whether their bone density is slipping between scans. This bone mass calculator does both. The estimate mode works out bone mass from your sex, weight and height using the Boer lean body mass equation. The tracker mode turns two bone density readings into a percentage loss, which is the figure clinicians actually watch over time.
Both results are estimates, not measurements. A formula cannot see inside your bones, and nothing here diagnoses osteopenia or osteoporosis. What it can do is give you a sensible starting number, show you exactly how that number was produced, and tell you plainly when a real DEXA scan is the right next step.
This calculator estimates. It does not diagnose any condition, and a percentage from two scans is only meaningful when both readings came from the same site on comparable equipment. Bring scan reports, not calculator printouts, to a medical appointment.
Quick Answer
Key takeaways
- The estimate runs on the Boer equation, which needs kilograms and centimetres. The calculator converts your pounds and inches first. Skipping that conversion is the single most common bone mass error online, and it cuts the answer nearly in half.
- Bone mass here is a fixed share of lean mass: 15% for men, 13% for women. Two people with the same lean mass get the same bone estimate, whatever their age, because age is not in the equation.
- The status bands come from bone mass as a share of body weight: Normal is 10 to 13% for men and 8 to 10.5% for women.
- The tracker mode answers a different question from the estimate mode. An estimate guesses your skeleton's weight today; the tracker measures change between two real scan readings.
- Quick Answer
- How the two modes divide the work
- The Boer equation and the bone fraction, step by step
- Worked example: the pre-filled man, plus a second case
- Reading the status bands without over-reading them
- Bone mass, bone density and lean mass are three different numbers
- When an estimate is not enough: the DEXA line
- What competing calculators miss
- Frequently Asked Questions
- Add This Calculator to Your Website
How the two modes divide the work
Use the estimate mode when you have never had a scan and want a ballpark. Use the tracker when you already have two DEXA readings and want the change between them in one number.
In estimate mode you pick your sex, enter weight in pounds, height in inches and age, then press Calculate. You get estimated bone mass in pounds, bone mass as a percentage of body weight, estimated lean body mass, and a status label. In tracker mode you enter the earlier and current bone mineral density values in g/cm², taken from your scan reports, and you get the percentage change plus a plain-language note about its size. The two modes share no inputs, because they share no data: one works from a tape measure and a scale, the other from a scanner.
One honest disclosure, because most pages hide it: the age field does not change the estimate. The Boer equation has no age term. Age is collected because it matters clinically (bone density typically peaks in the late twenties and declines after that, faster for women after menopause), and because readers expect to enter it, but a 30-year-old and a 60-year-old with the same sex, weight and height receive the same estimate here. Treat that as a known limit of formula estimates, not a bug.
The Boer equation and the bone fraction, step by step
The estimate is built in three steps: convert units, estimate lean body mass with the Boer equation, then take the bone share of that lean mass.
Convert to metric. Weight in pounds is divided by 2.20462 to get kilograms. Height in inches is multiplied by 2.54 to get centimetres. The Boer coefficients only work in these units.
Estimate lean body mass. Men: 0.407 x weight (kg) + 0.267 x height (cm) - 19.2. Women: 0.252 x weight (kg) + 0.473 x height (cm) - 48.3. The result, in kilograms, is converted back to pounds.
Take the bone share. Bone mass is 15% of lean body mass for men and 13% for women, the fractions body-composition scales use. Bone percentage is then bone mass divided by total body weight, times 100.
The Boer equation comes from Boer (1984), Estimated lean body mass as an index for normalization of body fluid volumes in humans, published in the American Journal of Physiology. It stays in clinical use because its linear form behaves sensibly across ordinary adult body sizes, unlike the older James equation, which bends downward at high body mass. The same height and weight inputs drive a different body estimate on the body surface area calculator, which sizes the skin surface for dosing rather than the lean tissue underneath it.
Worked example: the pre-filled man, plus a second case
The calculator is pre-filled with a 30-year-old man, 170 lbs, 70 inches. Run the steps by hand and you land exactly where the tool lands:
| Step | Value |
|---|---|
| Weight converted (170 / 2.20462) | 77.11 kg |
| Height converted (70 x 2.54) | 177.8 cm |
| Lean mass (0.407 x 77.11 + 0.267 x 177.8 - 19.2) | 59.66 kg, or 131.5 lbs |
| Bone mass (0.15 x 131.5) | 19.7 lbs |
| Bone percentage (19.7 / 170 x 100) | 11.6% |
| Status (men: Normal at 10 to 13%) | Normal |
A second case shows the women's equation. A woman of 140 lbs and 65 inches converts to 63.50 kg and 165.1 cm. Lean mass is 0.252 x 63.50 + 0.473 x 165.1 - 48.3 = 45.79 kg, or 101.0 lbs. Bone mass is 0.13 x 101.0 = 13.1 lbs, which is 9.4% of body weight: Normal on the women's band. Both sets of figures are what the calculator returns for those inputs, not rounded teaching numbers.
Reading the status bands without over-reading them
The status label compares your bone percentage with the bands body-composition devices commonly report. It describes where an estimate falls, nothing more.
| Bone % of body weight | Men | Women |
|---|---|---|
| Below the band | Under 10% Below Average | Under 8% Below Average |
| Inside the band | 10 to 13% Normal | 8 to 10.5% Normal |
| Above the band | Over 13% Above Average | Over 10.5% Above Average |
Two cautions belong with that table. First, the percentage moves when body weight moves, even if your skeleton does not change: gain fat and the same bones become a smaller share of you, which can drag the label down without any bone being lost. Second, a Below Average label from a formula is a prompt to ask about a real scan, not a finding. Diagnosis runs on measured density and fracture history. The National Institute of Arthritis and Musculoskeletal and Skin Diseases explains what bone mineral density numbers mean, including the T-scores and Z-scores a DEXA report actually uses, none of which a weight-and-height formula can produce.
Bone mass, bone density and lean mass are three different numbers
Bone mass is the total weight of the skeleton. Bone density is how much mineral sits in a given area of bone, reported in g/cm². Lean body mass is everything you weigh that is not fat: muscle, organs, water and bone together.
Confusing the first two causes most of the anxiety around this topic. A person can carry a normal weight of bone with low density inside it, because density is about packing, not size. That is why clinicians track density for fracture risk and why the tracker mode on this page takes density readings rather than weights. It is also why a smart scale's bone mass readout and a DEXA report can disagree without either being broken: they are reporting different quantities, one estimated from lean mass and one measured by X-ray absorption.
Where lean mass earns its keep is as the working tissue figure: it drives resting calorie burn and scales protein needs better than total weight does. Weight-bearing exercise is the lifestyle lever most often tied to both lean mass and bone health, and the BMI walking calculator prices the walking side of that equation, how much walking a weight goal actually takes.
When an estimate is not enough: the DEXA line
A DEXA scan is the clinical standard because it measures bone mineral density directly at the hip and spine. An online estimate is a screen you run at home; a scan is evidence a doctor can act on.
Between scans, the habits with real evidence behind them are unglamorous: enough calcium and vitamin D, regular weight-bearing and resistance exercise, not smoking, and moderate alcohol. The tracker mode exists for the interval between those scans: enter the two readings honestly, note the percentage, and take anything in the moderate or substantial range to your clinician instead of trying to interpret it alone.
What competing calculators miss
Search this topic and most of what ranks is a lean body mass calculator wearing a bone label, or a body-composition article with no working tool at all. Three gaps show up again and again.
Miss 1: the unit conversion. The Boer equation is metric. Pages that feed pounds and inches straight into its coefficients return lean mass figures roughly half the true size, and bone mass inherits the error. This calculator converts first (pounds to kilograms, inches to centimetres), computes, then converts back, and the worked example above shows every conversion so you can check it.
Miss 2: a tracker for people who already have scans. Estimator-only pages give a first number and stop. Anyone monitoring treatment or age-related loss needs the change between two density readings, which is a different calculation entirely. The tracker mode here does it, with the change bands the tool reports stated openly: under 10% mild, 10 to 25% moderate, 25% and over substantial.
Miss 3: the age disclosure. Nearly every bone tool asks for your age, implying it shapes the result. In this equation it does not, and this page says so next to the field itself. An estimate that hides its own limits invites more trust than it has earned.
Frequently Asked Questions
On this calculator's bands, a Normal result is bone mass of 10 to 13% of body weight for men and 8 to 10.5% for women. The worked example man lands at 11.6%, and a 140 lb, 65 inch woman lands at 9.4%. Absolute pounds vary with frame size, so the percentage and the trend over time say more than any single weight figure.
No. This calculator estimates bone mass from sex, weight and height. A DEXA scan directly measures bone mineral density and is the clinical standard used to diagnose osteopenia and osteoporosis. Use the estimate as a rough screen and the scan as the answer when the result matters.
Because readers expect it and because age matters clinically, but the Boer lean mass equation behind the estimate has no age term, so the age field does not change the number. Bone density typically peaks in the late twenties and then declines, faster for women after menopause, which is context a clinician uses even though the formula does not.
Bone mass is the total weight of your skeleton, in pounds or kilograms. Bone density is how tightly minerals are packed into a given area of bone, measured in g/cm², and it is the number doctors track for fracture risk. You can have a normal bone mass with low density, which is why the tracker mode on this page works from density readings.
Screening is commonly recommended for women at 65 and older, and for younger postmenopausal women at increased risk. Men are usually tested later or when risk factors appear, such as a fracture after 50, long-term corticosteroid use, or a family history of osteoporosis. People already being monitored often repeat scans every one to two years. Follow your doctor's schedule rather than a calculator's.
Significant loss is hard to fully reverse, but it can often be slowed or halted. Weight-bearing exercise, enough calcium and vitamin D, quitting smoking and limiting alcohol all help, and doctors may prescribe medication such as bisphosphonates when loss is severe. A tracker result in the moderate or substantial range is a reason to have that conversation promptly.
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References
- Boer P, "Estimated lean body mass as an index for normalization of body fluid volumes in humans," American Journal of Physiology, 1984: the original Boer equation this calculator uses for lean body mass. PubMed: Boer (1984), Estimated Lean Body Mass. Accessed October 2026.
- National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), "Bone Mineral Density Tests: What the Numbers Mean": how BMD results, T-scores and Z-scores are read, and who should be tested. NIAMS: Bone Mineral Density Tests. Accessed October 2026.
- National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), "Osteoporosis": causes, risk factors and prevention for low bone mass and osteoporosis. NIAMS: Osteoporosis Overview. Accessed October 2026.
- US Preventive Services Task Force, "Osteoporosis to Prevent Fractures: Screening" clinician summary: who screening is recommended for, and where the evidence is insufficient. USPSTF: Osteoporosis Screening Summary. Accessed October 2026.
- National Institute on Aging, "Osteoporosis": bone loss with aging, fall and fracture prevention, and treatment options for older adults. National Institute on Aging: Osteoporosis. Accessed October 2026.
- Mayo Clinic Press, "Understanding osteoporosis vs. osteopenia": the difference between low bone mass and osteoporosis, and how T-scores separate them. Mayo Clinic Press: Osteoporosis vs. Osteopenia. Accessed October 2026.