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Body fat calculator
Body fat percentage is the share of your weight that is fat. This calculator estimates it from a tape measure with the equations the U.S. Navy published in 1984: neck and waist for men, neck, waist and hips for women. It shows the result with the method’s error, because one tape reading is an estimate, not a measurement.
Calculate your body fat
Neck just below the larynx. Waist at the navel for men, at its narrowest for women. Hips at their widest. Tape flat on the skin, not pulled tight.
Body fat, Navy tape method
17.4%
Likely between 13.9 and 21.0%: against underwater weighing the equation is good to about 3.5 points either way (Hodgdon and Beckett, 1984).
Your numbers
| Fat mass | 31.4 lb |
|---|---|
| Fat-free mass | 148.6 lb |
| FFMI | 21.3 |
Next to published figures
| You | 17.4% |
|---|---|
| Adults at a normal BMI (Kyle et al., 2003) | 13.4 to 21.7% |
| Lean, by the cut-or-bulk check’s rule of thumb | under 15% |
| High, by the same rule of thumb | 20% or more |
Against DXA, this method read 2.5 to 2.6 points low in 430 male Marines (Potter et al., 2022). Treat one reading as a rough figure and watch the trend: same tape, same sites, same time of day.
Next: the FFMI calculator sets your fat-free mass against your height, and the cut or bulk check uses body fat to say where to start.
Show the math
- Waist minus neck: 48.3 cm.
- Body density (Hodgdon and Beckett, 1984): 1.0324 − 0.19077 × log10(48.3) + 0.15456 × log10(177.8) = 1.0590 g/cc.
- Body fat (Siri, 1961): 495 ÷ 1.0590 − 450 = 17.4%.
- Fat mass and fat-free mass: 81.6 kg × 17.4% = 14.2 kg, leaving 67.4 kg of fat-free mass.
For adults 19 and over. Not for pregnancy, or for anyone with a past or present eating disorder. General information, not medical advice.
How the Navy tape method works
The method predicts body density from two or three circumferences and your height, then converts density to body fat. Hodgdon and Beckett built the equations at the Naval Health Research Center in 1984 against underwater weighing (Hodgdon and Beckett, 1984a; Hodgdon and Beckett, 1984b), and the last step is Siri’s equation (Siri, 1961). All lengths are in cm.
- Men. Density = 1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height).
- Women. Density = 1.29579 − 0.35004 × log10(waist + hips − neck) + 0.22100 × log10(height).
- Both. Body fat % = 495 ÷ density − 450.
A man of 5 ft 10 in (178 cm) with a 15 in neck and a 34 in waist comes out at 17.4%. At 82 kg (180 lb) that is 14.2 kg of fat and 67.4 kg of fat-free mass. A woman of 5 ft 4 in (163 cm) with a 12.5 in neck, a 28 in waist and 38 in hips comes out at 27.0%.
Where to measure
Measure on bare skin, standing relaxed, with the tape level and flat but not pulled tight. Take each reading twice and use the average.
- Neck. Just below the larynx, the tape sloping slightly down toward the front.
- Waist, men. Level with the navel.
- Waist, women. At the narrowest point of the torso.
- Hips, women only. Around the widest part of the buttocks.
The men’s waist here is not the waist the cut or bulk check asks for. That one is taken midway between the bottom of the ribs and the top of the hips. Use each tool’s own site, or the numbers will not mean what the equations expect.
Small errors matter. At the man’s readings above, one more inch on the waist moves the result from 17.4% to 19.3%, and one more inch on the neck moves it to 15.5%.
How accurate is it?
Good to about 3.5 body fat points either way for men and 3.7 for women. That is each equation’s standard error against underwater weighing, with correlations of 0.90 and 0.85 (Hodgdon and Beckett, 1984a; Hodgdon and Beckett, 1984b). For the man above, the 17.4% is best read as somewhere between 13.9 and 21.0%.
Against DXA, the method leans one way for each sex. In 430 male and 179 female Marines aged 18 to 57, the tape read 2.5 to 2.6 points lower than DXA in men and 1.3 to 2.3 points higher in women (Potter et al., 2022). So a man’s tape result is more likely a little low than a little high, and a woman’s the reverse.
- Trust the trend. Between experienced observers the estimate repeats to within about 1 body fat point (Potter et al., 2022), far tighter than its agreement with a scan. A steady fall in your readings means something even when the body fat figure itself is off.
- Distrust the extremes. The equation takes waist minus neck, so a small waist with a thick neck reads very low: a man of 5 ft 10 in with a 30 in waist and a 17 in neck comes out at 4.0%. A result like that says more about the method than about you.
Body fat by waist and neck
For men, body fat rises about 1.9 points for each inch on the waist and falls about 2.0 for each inch on the neck, at the readings above. The tables hold height fixed; for yours, use the calculator.
Men
| Waist | Neck 14 in | Neck 15 in | Neck 16 in | Neck 17 in |
|---|---|---|---|---|
| 28 in (71 cm) | 6.5 | 4.0 | - | - |
| 30 in (76 cm) | 11.2 | 8.9 | 6.5 | 4.0 |
| 32 in (81 cm) | 15.5 | 13.4 | 11.2 | 8.9 |
| 34 in (86 cm) | 19.3 | 17.4 | 15.5 | 13.4 |
| 36 in (91 cm) | 22.9 | 21.1 | 19.3 | 17.4 |
| 38 in (97 cm) | 26.1 | 24.5 | 22.9 | 21.1 |
| 40 in (102 cm) | 29.2 | 27.7 | 26.1 | 24.5 |
| 42 in (107 cm) | 32.1 | 30.6 | 29.2 | 27.7 |
| 44 in (112 cm) | 34.8 | 33.4 | 32.1 | 30.6 |
Women
| Waist | Hips 34 in | Hips 38 in | Hips 42 in | Hips 46 in |
|---|---|---|---|---|
| 24 in (61 cm) | 16.0 | 21.6 | 27.0 | 32.1 |
| 26 in (66 cm) | 18.8 | 24.4 | 29.6 | 34.6 |
| 28 in (71 cm) | 21.6 | 27.0 | 32.1 | 36.9 |
| 30 in (76 cm) | 24.4 | 29.6 | 34.6 | 39.3 |
| 32 in (81 cm) | 27.0 | 32.1 | 36.9 | 41.6 |
| 34 in (86 cm) | 29.6 | 34.6 | 39.3 | 43.8 |
| 36 in (91 cm) | 32.1 | 36.9 | 41.6 | 46.0 |
| 38 in (97 cm) | 34.6 | 39.3 | 43.8 | 48.2 |
| 40 in (102 cm) | 36.9 | 41.6 | 46.0 | 50.3 |
What is a normal body fat percentage?
Among adults whose BMI is in the normal range, body fat ran from 13.4 to 21.7% in men and from 24.6 to 33.2% in women, in a study of 5,635 Swiss adults measured by bioelectrical impedance (Kyle et al., 2003). No agreed scale sorts body fat into grades, and a tape reading will not line up exactly with figures taken another way.
For deciding what to do next, the cut or bulk check on this site treats under 15% for men and under 25% for women as lean, and 20% or 30% and over as high. Those lines are a rule of thumb, not a study result, and that page says so.
What to do with the number
- See how much muscle you carry. The FFMI calculator divides your fat-free mass by your height squared and sets it beside published figures.
- Check your maintenance calories. The maintenance calculator takes body fat for a second estimate from lean mass.
- Set protein on a cut. The cutting calculator uses lean mass for its protein range when you give it body fat.
- Decide whether to cut or bulk. The cut or bulk check starts from body fat or waist.
Questions
How accurate is the Navy body fat calculator?
Good to about 3.5 body fat points either way for men and 3.7 for women, measured against underwater weighing (Hodgdon and Beckett, 1984). Against DXA scans in Marines it read 2.5 to 2.6 points low in men and 1.3 to 2.3 points high in women (Potter et al., 2022). Use it to follow a trend, not to settle a single figure.
Where do you measure for the Navy body fat method?
Neck: just below the larynx, with the tape sloping slightly down toward the front. Waist, for men: level with the navel. Waist, for women: at its narrowest point. Hips, for women only: around the widest part of the buttocks. Keep the tape flat on the skin and level, and do not pull it tight.
What is a normal body fat percentage?
Among adults whose BMI is in the normal range, body fat ran from 13.4 to 21.7% in men and from 24.6 to 33.2% in women (Kyle et al., 2003). Those figures were measured by bioelectrical impedance, so a tape reading will not match them exactly.
Why does the calculator ask for my neck?
The equation takes your waist minus your neck, so a thicker neck at the same waist reads leaner. For a man of 5 ft 10 in with a 34 in waist, a 15 in neck gives 17.4% and a 16 in neck gives 15.5%. That is also why a small error in either reading moves the result.
Is a tape measure as good as a DXA scan?
No. In 609 Marines the tape and DXA disagreed by a few points on average, in opposite directions for men and women, and by more for some individuals (Potter et al., 2022). The tape costs nothing and, between experienced observers, repeats to within about 1 point, which makes it better for tracking change than for one exact number.
Who should not use this calculator?
It is built for adults 19 and over. It is not for pregnancy, and it is not a good idea for anyone with a past or present eating disorder or for anyone whom body measurements distress. It is general information, not medical advice, and no number here is a target.
Sources
- Hodgdon JA, Beckett MB (1984). Prediction of percent body fat for U.S. Navy men from body circumferences and height. Naval Health Research Center, San Diego, Report No. 84-11. apps.dtic.mil/sti/tr/pdf/ADA143890.pdf
- Hodgdon JA, Beckett MB (1984). Prediction of percent body fat for U.S. Navy women from body circumferences and height. Naval Health Research Center, San Diego, Report No. 84-29. apps.dtic.mil/sti/tr/pdf/ADA146456.pdf
- Kyle UG, Schutz Y, Dupertuis YM, Pichard C (2003). Body composition interpretation: contributions of the fat-free mass index and the body fat mass index. Nutrition 19(7-8):597-604. doi:10.1016/S0899-9007(03)00061-3
- Potter AW, Tharion WJ, Holden LD, et al. (2022). Circumference-based predictions of body fat revisited: preliminary results from a US Marine Corps body composition survey. Frontiers in Physiology 13:868627. doi:10.3389/fphys.2022.868627
- Siri WE (1961). Body composition from fluid spaces and density: analysis of methods. In: Techniques for Measuring Body Composition, National Academy of Sciences, pp. 223-244. Reprinted in Nutrition 9(5):480-491 (1993). pubmed.ncbi.nlm.nih.gov/8286893/
Each figure quoted from a study was checked against the paper, or its abstract where the full text could not be read. Found an error? Email founder@topsets.app and the page will be corrected and its date updated.