Body Fat (DEXA Estimate) Calculator
The formula
What the body fat (dexa estimate) tells you
Tape-meat body composition for body fat (dexa estimate): the US Navy circumference method — the field standard gyms and physicals actually use — with fat and lean mass in kilograms.
Calculation: US Navy: BF% = 86.010·log₁₀(waist−neck) − 70.041·log₁₀(height) + 36.76 (men); +1.08·…−84.52 women. Enter your inputs and every substitution is shown below the result.
Reading the result
Track the trend monthly under the same conditions; ±2 points of tape error is normal.
Limitations and best practice
Hydration and recent meals shift centimetres — measure fasted, morning, same spot.
This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Frequently asked questions
How accurate is tape-meat body fat?
Which formula is best for me?
Source & methodology
US Navy Body Composition Program method.
How Body Fat (DEXA Estimate) works — and what your result really means
Budgets fail on the numbers nobody wrote down — this tool forces every one of them into the open. Searchers land on a Body Fat (DEXA Estimate) page for three reasons — to plan, to compare options, and to check that somebody else’s arithmetic is honest. This tool serves all three, and everything after the calculator explains the model instead of hiding it.
Most confusion about Body Fat (DEXA Estimate) comes from mixing up the input you control with the input you merely observe. The formula treats them identically, but your decisions should not: one deserves measurement, the other deserves a defensible estimate.
A calculation like this one is worth roughly as much as a careful sentence: it forces several vague considerations into one comparable quantity. Once Body Fat (DEXA Estimate) is on the table, the argument can stop being about impressions.
What makes a calculation page trustworthy is that its copy is derived from its own arithmetic: here body fat = 31.7%, recomputed every time a field changes, and the sensitivity section ranks the inputs that move the result — Waist / hip circumference first, at ≈20.8 % of the headline for a ten-percent error either way in that input. Work down the page and by the end you could re-derive the result in a spreadsheet from memory.
Every input in Body Fat (DEXA Estimate), and what it does to the answer
One formula, published in full: US Navy: BF% = 86.010·log₁₀(waist−neck) − 70.041·log₁₀(height) + 36.76 (men); +1.08·…−84.52 women. Anything you can read, you can reproduce in a spreadsheet, and that reproducibility is the whole point of printing it rather than hiding it behind a button.
Weight (kg) (example value 54) is a plain measured quantity — the unit shown in the label is the unit the formula expects. Use the same conditions each time (same scale, same time of day) so that changes in the output reflect real change.
Height (cm) (example value 180) is a numeric input whose unit is fixed by the label; a wrong unit is a wrong answer wearing a plausible disguise. Measure twice and use the unit the label asks for — length terms often scale the result geometrically.
Neck / waist circumference (cm) (example value 37) is a plain measured quantity — the unit shown in the label is the unit the formula expects. If you are unsure what belongs in this field, look at the printed steps: the substitution shows exactly how the engine uses it.
Waist / hip circumference (cm) (example value 97) is a numeric input whose unit is fixed by the label; a wrong unit is a wrong answer wearing a plausible disguise. If you are unsure what belongs in this field, look at the printed steps: the substitution shows exactly how the engine uses it.
Sex (example value Male) is a choice rather than a quantity — pick the option that matches your situation, because the calculation path branches here. Replace the example with the figure from your own records — the tool recomputes instantly and the printed steps follow your numbers.
What each “Sex” choice actually does: Male → 31.7% · Female → 2.0% These figures are computed from this engine, not estimated — switch the dropdown above and you will land on exactly these numbers.
A fully worked Body Fat (DEXA Estimate) example
The tool prints its own working; this is the same arithmetic on the example values, reproduced so you can follow it by hand. Starting figures: Weight (kg), Height (cm), Neck / waist circumference (cm), Waist / hip circumference (cm). The endpoint of that chain is 31.7% of body fat, sitting in the “Above the healthy band — the trend matters more than today’s point” band.
- Circumference difference waist−neck = 60.0 cm
- Navy formula (log₁₀ terms) → 31.7 %
- Fat mass = 54.0 × 31.7 % = 17.1 kg
Fat mass — 17.1 kg. Compare it against the main result of 31.7% before drawing conclusions.
Lean mass — 36.9 kg. Read next to the headline, this is the figure that shows the shape of the trade-off.
BMI — 16.7. Read next to the headline, this is the figure that shows the shape of the trade-off.
Overwrite any input above and every line of this example updates with it — the substitution is live, not a screenshot of somebody else’s numbers.
Scenario table: Body Fat (DEXA Estimate) at ±10 % and ±20 % of the key input
Read this table as the practical error bar on the headline figure. It answers the question people actually have after seeing a single number: how wrong could this be if the main input is off by ten or twenty percent?
| Waist / hip circumference setting | Body fat |
|---|---|
| 80 % of the example value | 17.1% |
| 90 % of the example value | 25.2% |
| example inputs | 31.7% |
| 110 % of the example value | 37.3% |
| 120 % of the example value | 42.2% |
That spread — 17.1% at the low end, 42.2% at the high — is what a careful read of Body Fat (DEXA Estimate) looks like: a band you can state out loud, with the reason for each edge. Reproduce it in the form above by editing Waist / hip circumference alone; the substitution steps will follow your figures exactly.
The levers behind Body Fat (DEXA Estimate), ranked by effect
Nobody should have to guess which input matters. The engine was re-run once per field below — ten percent up, ten percent down, everything else frozen — and the results ranked by how far they moved the body fat. For Body Fat (DEXA Estimate) the ranking is measured rather than guessed, and it belongs to these defaults: shift the starting point and the order can shift with it.
- Waist / hip circumference +10 % → Body Fat (DEXA Estimate) = 37.3% · −10 % → 25.2% (the body fat shifts ≈20.8 %)
- Height: ten percent up gives 28.8%, ten percent down gives 34.9% — ≈10.1 % of the body fat either way
- Neck / waist circumference: ten percent up gives 29.4%, ten percent down gives 34.0% — ≈7.5 % of the body fat either way
Waist / hip circumference is the dominant lever here: ten percent either way moves the result by about 20.8 %, from 25.2% to 37.3%. Spend your verification effort there first, and treat Height as the second priority (≈10.1 % per ten percent). The rest of the inputs earn only a rounding-error of attention, and that asymmetry is the practical payoff of measuring rather than asserting.
What a Body Fat (DEXA Estimate) of 31.7% means in practice
Nobody acts on a bare figure — they act on a figure with a comparison attached. The verdict attached to the default calculation — “Above the healthy band — the trend matters more than today’s point” — is one band on a ladder your own figure may sit somewhere else on. The sensitivity list shows how far a modest input error moves you along that ladder: for Waist / hip circumference, ±10 % covers 25.2% to 37.3%. The practical reading rules: ask what would have to change to move you one band. If the answer is “a small, plausible input difference”, the band itself is not the finding — the uncertainty is.
Set Body Fat (DEXA Estimate) beside its neighbours and it usually plays a specific role: this figure establishes the size of something, and the neighbouring tools establish whether that size is acceptable. Skipping the first step makes the second one arbitrary.
How people get Body Fat (DEXA Estimate) wrong
Hydration and recent meals shift centimetres — measure fasted, morning, same spot. This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Using stale inputs. Body Fat (DEXA Estimate) is only as current as the numbers behind it — an estimate carried over from a previous season, rate table or report quietly biases every output. Re-measure the inputs first; that single habit fixes more bad Body Fat (DEXA Estimate) figures than any formula change.
This model has its own particular trap: Waist / hip circumference carries ≈20.8 % of the response per ten percent of error, so effort spent elsewhere is largely decorative.
Another is comparing across contexts: a Body Fat (DEXA Estimate) computed with one set of conventions should never be lined up against a figure computed with another. Check the inputs behind both before ranking them.
Before you trust your Body Fat (DEXA Estimate): a short checklist
- Confirm the example values are plausible for your own situation before replacing them.
- Note the date and the inputs beside the number so the figure can be audited later.
- Re-verify Waist / hip circumference against a source document — ten percent of error there moves the headline by ≈20.8 %.
- Verify each input against its original source document, not memory.
- Compare the output against one published benchmark or a colleague’s independent estimate.
- Confirm the answer against one independent method or published benchmark for Body Fat (DEXA Estimate).
How to use the Body Fat (DEXA Estimate) tool properly
The tool does the arithmetic; the routine below is what makes the arithmetic trustworthy. Five steps, a minute total — and afterwards you will know not just what the number is, but which assumption produced it.
Step 1 — gather before you type. Body Fat (DEXA Estimate) depends on weight (kg), height (cm), neck / waist circumference (cm), waist / hip circumference (cm), sex. Collect them from a source document — a statement, a report, an invoice, a log — rather than from memory, because recalled inputs are the single largest cause of wrong results. Note the assumption you are least sure about; that is where the real risk lives.
Step 2 — compute the version you would not be embarrassed by. If a stranger audited your inputs, which set would you hand over? Enter that set, read the result, and treat everything else as upside. Say the answer out loud before you save it; if it sounds wrong, the model did not change, your understanding did.
Step 3 — measure what deserves measuring. The ranked levers above tell you where a careful figure pays off. Everything else can stay approximate, which is a licence to stop hunting for data you do not need. A figure nobody can reproduce is a figure nobody will act on twice.
Step 4 — stress before you commit. A decision that survives a ten-percent squeeze on its two biggest inputs needs no luck to be sound. One that does not survive is a decision about hope, not about arithmetic. A figure with a date beside it becomes evidence; without one it stays an anecdote.
Step 5 — record the context, not just the number. Note today’s date and the inputs alongside the 31.7% output. Six months from now the context is what turns this figure into a trend. Say the answer out loud before you save it; if it sounds wrong, the model did not change, your understanding did.
Who actually uses Body Fat (DEXA Estimate) — and when
In Body Measurements the figure computed here is usually the first one somebody asks to see. Having it — with the formula behind it — changes your position in the conversation from participant to reference. Write the assumptions in the same file as the result, and future arguments take minutes instead of meetings.
The audience for this page is planners sizing a spend before committing money. In professional Body Measurements practice the pattern is always the same — screen with Body Fat (DEXA Estimate), then invest slow analysis only in whatever survives the screen. Suspiciously tidy answers deserve the same scrutiny as untidy ones.
Re-running this page costs nothing and catches the slow drifts that never announce themselves. In Health & Medical the expensive mistakes are rarely sudden; they are small changes in Weight (kg) that nobody recalculated for a year. Comparisons are cheap: run the identical calculation for the alternative and look at the gap.
Body Fat (DEXA Estimate) — frequently asked questions
What affects Body Fat (DEXA Estimate) the most?
Body Fat (DEXA Estimate) is driven above all by Waist / hip circumference. Perturbing only that field by ten percent either way produced 37.3% against the 31.7% baseline — a ≈20.8 % response, while Height manages ≈10.1 %.
Which matters more: height or waist / hip circumference?
For Body Fat (DEXA Estimate), Waist / hip circumference wins the head-to-head (≈20.8 % against ≈10.1 % per ten-percent change). Knowing which input dominates is the difference between careful work and merely slow work.
How much does the “Sex” choice change the answer?
Across every option this tool offers, the body fat ranges from 2.0% (Female) to 31.7% (Male) with all other inputs held at their example values. The per-option table is printed in the inputs section — this is a decision that genuinely moves the number, not a cosmetic dropdown.
What is a typical Body Fat (DEXA Estimate)?
With the example inputs on this page the result is 31.7%, labelled “Above the healthy band — the trend matters more than today’s point”. “Typical” varies with situation, which is why every result here ships with its verdict band and its sensitivity list: they turn one figure into a range you can locate yourself inside.
How do I calculate Body Fat (DEXA Estimate) by hand?
US Navy: BF% = 86.010·log₁₀(waist−neck) − 70.041·log₁₀(height) + 36.76 (men); +1.08·…−84.52 women is the entire method. Work the inputs in that order — Circumference difference waist−neck = 60.0 cm — and you will reach 31.7% on the default figures, the same number this tool prints.
What happens to Body Fat (DEXA Estimate) if waist / hip circumference changes by 10 %?
Try it in the form above and the printed substitution will follow you; the pre-computed answer for the defaults is 25.2% to 37.3% across the ten-percent probe, i.e. ≈20.8 % sensitivity on the body fat.
Is the Body Fat (DEXA Estimate) result of 31.7% good or bad?
The tool answers “what”, not “whether”: 31.7% carries the verdict “Above the healthy band — the trend matters more than today’s point” for the default case, which is a starting interpretation rather than a verdict on your situation. Re-run with your own figures and compare the bands.
Is Body Fat (DEXA Estimate) accurate?
The arithmetic is exact: US Navy: BF% = 86.010·log₁₀(waist−neck) − 70.041·log₁₀(height) + 36.76 (men); +1.08·…−84.52 women is evaluated with full floating-point precision and every substitution is printed in the worked example. What limits accuracy is input quality and the model’s assumptions, so treat the 31.7% result as the correct answer to the question you typed — and check the assumptions section before acting on it.
Can Body Fat (DEXA Estimate) be negative or empty?
Yes, and that is informative rather than broken: a negative Body Fat (DEXA Estimate) usually means the inputs encode an outflow or a shortfall, and the verdict band above labels exactly that situation instead of hiding it.
How accurate is tape-meat body fat?
±3 points versus DEXA in lean subjects, better in groups; the trend is reliable even when the level is soft.
Which formula is best for me?
Consistency beats formula choice — the same method, same conditions, every time.
Is my data private on this page?
Yes — computation happens locally in your browser, with no account, no tracking of your inputs and nothing sent to a server. The printed formula is the whole story of what happens to your figures.
Key terms on this page
- Fat mass
- 17.1 kg in the default Body Fat (DEXA Estimate) calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- Lean mass
- 36.9 kg in the default Body Fat (DEXA Estimate) calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- BMI
- 16.7 on the example inputs — a companion figure printed beside the headline of Body Fat (DEXA Estimate) so that no result is read in isolation.
- Body fat
- The primary output of this tool: 31.7% for the default inputs, computed exactly from US Navy: BF% = 86.010·log₁₀(waist−neck) − 70.041·log₁₀(height) + 36.76 (men); +1.08·…−84.52 women.
- Worked example
- Every substitution in order, from the example inputs to 31.7% — the audit trail for the headline figure.
- Verdict band
- The interpretation attached to a result (“Above the healthy band — the trend matters more than today’s point” on these inputs), which turns a bare number into a position on a scale.
- Sensitivity (±10 %)
- How far the Body Fat (DEXA Estimate) moves when a single input is nudged ten percent either way; the ranked list on this page is computed live from this engine.
Methodology, sources and limits
Everything above runs on one stated formula, applied without hidden coefficients: US Navy: BF% = 86.010·log₁₀(waist−neck) − 70.041·log₁₀(height) + 36.76 (men); +1.08·…−84.52 women. Source of record: US Navy Body Composition Program method. Any other implementation of this model should return the same figure for the same inputs. If one does not, the difference is in its assumptions — which this page prints and that one probably does not.
Treat the output as a precise answer to the question you typed: exact arithmetic, transparent formula, published source, no hidden rounding. The design constraint was set by usefulness rather than by comfort: an estimate you can interrogate beats an answer you have to trust.
Turning this Body Fat (DEXA Estimate) into a decision
Add the costs the estimate omits first — fees, waste, contingency — then re-run before treating the figure as a budget line.
This page was written for planners sizing a spend before committing money, and the promise is that nothing above required trust. Bookmark the tool, re-run it whenever an input moves by more than a few percent, and keep the date with the number.