Free body fat calculator using the U.S. Navy tape method: how to measure, how to read your result without chasing extremes, and how it compares with DXA and smart scales.
Key takeaways
- The tape-measure method agreed with DXA scans with intraclass correlations of 0.83 in women and 0.72 in men; waist size affected accuracy.[1]
- Foot-to-foot impedance scales agreed less well with lab methods for individuals than hand-and-foot devices.[2]
- There is no single agreed healthy body fat range; body fat at the same BMI differs with sex, age and ethnic group.[3]
- BMI cannot separate fat from muscle, which is why a body fat estimate or a waist measure adds useful context.[5]
In short: This body fat calculator estimates your body fat percentage from your height and a few tape measurements, using the U.S. Navy method. All you need is a soft tape measure. It is a useful way to watch your trend over time, but it is an estimate: in a study against DXA scans, it agreed reasonably well overall and was less precise for some people, especially men and people with larger waists.
Body fat calculator (U.S. Navy method)
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Educational estimate, not medical advice. Talk with a healthcare professional before changing how you eat, move or take medicines.
How this works
The U.S. Navy method (Hodgdon and Beckett, 1984) estimates body fat from circumferences and height, using logarithms of waist minus neck (men) or waist plus hip minus neck (women).
Men: 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450. Women: 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450 (all in cm).
Reference ranges are the American Council on Exercise general categories. Essential fat (about 2-5% for men, 10-13% for women) is a minimum for health, not a target.
Limits
- Usually within a few percentage points of lab methods, but can be further off for very lean, very muscular or larger bodies.
- Measure the same way each time; the trend tells you more than one number.
- Lower is not always better: very low body fat harms hormones, bones and health.
Sources
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center reports 84-11 and 84-29, 1984
- American Council on Exercise: body fat percentage categories
How to measure for a reliable result
- Use a flexible, non-stretch tape. Keep it snug on the skin without pressing in, and level all the way around.
- Stand relaxed, feet together, and breathe out normally before you read the waist number. Do not pull your stomach in.
- Measure at the spots described under each box, at the same time of day (morning works well), before exercise.
- Take each measurement two or three times and use the average. If you can, ask someone to help with the neck and hips.
Reading your result without chasing extremes
The calculator places your result in general fitness categories. Treat them as wide bands, not targets. There is no officially agreed “healthy” body fat range: researchers who tried to build one from BMI guidelines found that the body fat that goes with a given BMI depends on sex, age and ethnic group. That is why the calculator uses separate bands for women and men.
Very low body fat is not a health goal: the lowest band is a minimum, not something to aim for. If you find yourself fixating on a number, it may help to talk with someone; our guide to body image is a kind place to start.
How accurate is it compared with DXA and smart scales?
DXA scans and other lab methods are the reference, but they cost money and are not available to most people. Home methods trade some accuracy for convenience:
- Tape measure (this calculator). In 76 active-duty service members, the circumference method agreed with DXA with an intraclass correlation of 0.83 for women and 0.72 for men; waist size and sex both affected accuracy.
- Bioelectrical impedance. An eight-point (hand and foot) device agreed more closely with DXA in the same study. A German comparison found that simple foot-to-foot bathroom-scale devices agreed less well for individuals than devices with hand and foot electrodes, though they did better for group averages.
| Item | Women | Men |
|---|---|---|
| Tape measure (this method) | 0.83 | 0.72 |
| Eight-point impedance device | 0.93 | 0.89 |
One study in active-duty service members; waist size and sex also affected how close the tape-measure estimate came.
Source: Combest TM et al., Military Medicine 2017 (checked on October 6, 2026)
Whatever you use, stick with one method and compare like with like. Our guide to smart scales explains what different scales measure.
Why your weight and body fat can move differently
If you start strength training, the scale may move slowly while your waist and body fat drop, because you are adding some muscle as you lose fat. The American College of Sports Medicine notes that resistance training does not add much to weight loss on its own but may increase lean mass and fat loss. That is a good outcome, and it is one reason to track a tape measurement or body fat estimate alongside your weight rather than the scale alone.
Who this calculator is for
The equations were developed from measurements of U.S. Navy men and women, so they are meant for adults. They are not designed for children and teens, whose bodies are still changing; a pediatrician can explain growth and body composition for young people. During pregnancy, waist and hip measurements change for reasons that have nothing to do with fat, so the result does not apply.
Body fat, BMI and waist: which to use?
Each answers a different question. BMI is a quick screen based on weight and height. Body fat percentage tells you how much of your weight is fat. Your waist, and the waist-to-height ratio, tell you about fat around the middle, the kind most linked with health risks; see our guide to visceral fat. Together they give a fuller picture than any one number.
What to do with your result
If you want to lower body fat, the aim is to lose fat while keeping muscle. That usually means a modest calorie deficit, enough protein (the protein calculator gives a range) and regular strength training. If your weight is fine but you would like more muscle and less fat, our guide to body recomposition explains how that works. Re-measure every four weeks or so: the trend tells you far more than a single reading.
Track your trend
- Same tape, same timeMeasure in the morning, before exercise, at the spots shown in the calculator.
- Average two or three readingsUse the mean of each measurement, ideally with a helper for neck and hips.
- Re-measure every four weeksCompare like with like: one method, one set of conditions.
- Read it with your waist and weightTogether they say more than any single number.
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- Would a DXA scan or another body composition test be useful for me?
- Given my age and health, what body fat range is reasonable to aim for?
- How can I lose fat while protecting muscle and bone?
- Is my waist size a concern for my heart or blood sugar?
Frequently asked questions
What is a healthy body fat percentage?
There is no single official range. Healthy levels differ for women and men and shift with age and ethnic background. The categories in the calculator are broad fitness bands, not targets; your clinician can help you interpret yours.
How accurate is the Navy body fat method?
It is a reasonable estimate for many people but less precise for some. In one study it agreed better with DXA scans in women than in men, and accuracy changed with waist size.
Is a smart scale more accurate than a tape measure?
Not necessarily. Foot-to-foot scales agreed less well with lab methods for individuals. Devices with hand and foot electrodes did better in studies. Whatever you choose, use it the same way each time.
How often should I measure my body fat?
Every four weeks or so is enough. Body fat changes slowly, and measuring too often mostly shows measurement noise.
Can I lose fat from one area by exercising it?
Not in a meaningful way. In a randomized study, six weeks of daily abdominal exercises strengthened the muscles but did not reduce belly fat. Our belly fat guide explains what does help.
References
- Combest TM, Howard RS, Andrews AM. Comparison of Circumference Body Composition Measurements and Eight-Point Bioelectrical Impedance Analysis to Dual Energy X-Ray Absorptiometry to Measure Body Fat Percentage. Military Medicine, 2017. doi:10.7205/MILMED-D-16-00344 · PMID 28810989 (accessed October 6, 2026) Other
- Bosy-Westphal A, Later W, Hitze B, et al.. Accuracy of bioelectrical impedance consumer devices for measurement of body composition in comparison to whole body magnetic resonance imaging and dual X-ray absorptiometry. Obesity Facts, 2008. doi:10.1159/000176061 · PMID 20054195 (accessed October 7, 2026) Other
- Gallagher D, Heymsfield SB, Heo M, Jebb SA, Murgatroyd PR, Sakamoto Y. Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index. American Journal of Clinical Nutrition, 2000. doi:10.1093/ajcn/72.3.694 · PMID 10966886 (accessed October 6, 2026) Other
- Vispute SS, Smith JD, LeCheminant JD, Hurley KS. The effect of abdominal exercise on abdominal fat. Journal of Strength and Conditioning Research, 2011. doi:10.1519/JSC.0b013e3181fb4a46 · PMID 21804427 (accessed October 7, 2026) Randomized trial
- About Body Mass Index (BMI). Centers for Disease Control and Prevention. (accessed October 7, 2026) Government page
- Overweight and obesity management (NG246): identifying and assessing overweight, obesity and central adiposity. National Institute for Health and Care Excellence (NICE), 2025. (accessed October 7, 2026) Guideline
- Donnelly JE, Blair SN, Jakicic JM, et al.. American College of Sports Medicine Position Stand: Appropriate physical activity intervention strategies for weight loss and prevention of weight regain for adults. Medicine & Science in Sports & Exercise, 2009. doi:10.1249/MSS.0b013e3181949333 · PMID 19127177 (accessed October 7, 2026) Society statement
Facts checked on October 6, 2026
Educational information, not medical advice. Talk with a qualified healthcare professional about your own situation. In an emergency call 911.