How to Take the Measurements

The formula comes from studies that measured people at set sites, so the same sites are used here. Keep the tape against the skin without pressing in. Measure your waist after breathing out normally, and read the tape to the nearest 0.5 cm.

• Neck. Measure just below the voice box, with the tape sloping slightly down to the front.
• Waist, men. Measure at the level of the navel.
• Waist, women. Measure at the narrowest part of the abdomen, about midway between the bottom of the breastbone and the navel.
• Hips, women. Measure around the part of the buttocks that sticks out the most.

For women, the waist site here sits higher than the health check for waist size, which measures halfway between the lowest rib and the top of the hip bone, roughly in line with the belly button. For men, the two sites sit close together, but the formula was built on the navel. The risk cut-offs of 80 cm for women and 94 cm for men belong to that health check (healthdirect) and say nothing about this percentage. To learn more, read what visceral fat is and why it matters.

How the Calculation Works

The formula first estimates body density from your measurements in centimetres. A second formula, from Siri (1961), turns density into a percentage. Weight and age did not enter the final formula in the Navy studies. The calculator uses your age only to pick a guide range.

• Women: density = 1.29579 - 0.35004 x log10(waist + hips - neck) + 0.22100 x log10(height)
• Men: density = 1.0324 - 0.19077 x log10(waist - neck) + 0.15456 x log10(height)
• Everyone: body fat % = (495 / density) - 450

Two worked examples show the arithmetic:

Body Fat Ranges by Age and Sex

The chart in the calculator shows these ranges, which match a healthy BMI.

The ranges come from one study of white and African American adults, and its authors called them provisional. Ranges for Asian adults in the same study sat higher. For the full picture, read ideal body fat percentage by age and sex.

How Far to Trust the Estimate

A tape measure formula has limits:

• Margin of error. The studies report a standard error of about 3.5 percentage points for men and 3.7 for women, so your true figure could sit several points either side of the result, and sometimes further. Checks on separate groups gave about 2.7 points for men and 4.0 to 4.4 for women.
• Who was studied. The formulas were developed with 602 male US Navy personnel aged 18 to 56 and 214 female personnel aged 18 to 44, not the Australian public. Body fat was checked against underwater weighing.
• Pregnancy. Waist measurements do not apply in pregnancy (healthdirect), so this estimate is not a guide at that time.
• Different methods. The formula and the guide ranges rest on different ways of measuring body fat, so the comparison is a rough guide only.
• DXA scans. A DXA scan, a form of X-ray used mainly in medicine and research, can measure body fat accurately (Better Health Channel), and it is not cheap (University of Sydney).

BMI is a separate check that uses your height and weight. Use the BMI calculator and healthy BMI range to see it, and read does muscle weigh more than fat for how muscle changes the picture.

What to Do With Your Result

One number does not describe your health. Too much or too little body fat can increase the risk of illness, and where your body stores fat matters more than how much there is when assessing disease risk (Better Health Channel). It helps to look at the estimate alongside your waist, your wider health and your history. For more on fat around the middle, read what the evidence says about belly fat. If you measure again later, using the same sites keeps the numbers comparable.

If body fat is something you want to look at, Australia's guidelines on healthy eating and physical activity are a starting point:

• Healthy eating. Build meals from the five food groups, and limit foods and drinks with saturated fat, added salt, added sugars and alcohol. For the energy side, read what a calorie deficit is and how to work out yours, or use the calorie deficit calculator and the basal metabolic rate (BMR) calculator.
• Physical activity. Australia's guidelines for adults suggest 30 minutes or more of moderate to vigorous physical activity on most days, plus muscle-strengthening activities on 2 or more days a week. For ideas, read how many steps a day to lose weight and best exercises for belly fat.

Losing as little as 5% of your body weight can bring health benefits, such as a lower risk of heart disease or type 2 diabetes (healthdirect). Outcomes vary between individuals. To work out that figure, read how to calculate your weight loss percentage. For a step by step plan, see how to lose weight: a realistic guide. A GP or nurse practitioner can give advice on your own situation.

Frequently Asked Questions

How can I calculate my body fat percentage from my measurements?

You can measure your height, neck and waist, plus your hips if you are a woman, then enter them in the calculator above. It uses the US Navy formula, which needs only a tape measure and takes centimetres. Using the measuring sites on this page matters, because the formula was built on them.

How accurate is a body fat calculator?

A tape measure calculator gives an estimate only, and its margin of error is several percentage points against underwater weighing. Careful measuring matters, because a small tape error changes the result. In the worked examples above, 1 cm more on the waist moves the estimate by about 0.5 points for the woman and 0.7 points for the man.

How accurate are body fat scales?

Their accuracy is questionable. Researchers who tested smart scales found they massively over-estimated or under-estimated fat and muscle mass, according to a University of Sydney academic writing in The Conversation. A reading from home scales is best seen as a rough estimate. A tape measure gives you a second estimate to compare it with.

Can I work out my body fat from height and weight alone?

Not directly. Height and weight give you BMI, which is a guide to weight for height, and BMI cannot tell fat from muscle. This calculator uses your height, neck and waist instead, plus your hips if you are a woman. The two checks answer different questions, so you can use both.

Is the calculation different for women and men?

Yes. The Navy researchers built a separate formula for each. The formula for women adds hips and uses a different waist site, and the guide ranges for women sit higher than those for men at every age. Please choose the option that suits you, and ask a GP or nurse practitioner if you are unsure which ranges apply to you.

References

• Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men from body circumferences and height. Naval Health Research Center, Report 84-11, 1984. https://web.archive.org/web/20230706125208/https://apps.dtic.mil/sti/pdfs/ADA143890.pdf
• Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy women from body circumferences and height. Naval Health Research Center, Report 84-29, 1984. https://web.archive.org/web/20250202071332/https://apps.dtic.mil/sti/tr/pdf/ADA146456.pdf
• 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;72(3):694-701. doi:10.1093/ajcn/72.3.694. https://web.archive.org/web/20190324111411/https://academic.oup.com/ajcn/article/72/3/694/4729363
• healthdirect. Body mass index (BMI) and waist circumference. https://www.healthdirect.gov.au/procedures/health-screenings/body-mass-index-bmi-and-waist-circumference
• Better Health Channel (Victorian Government). Body mass index (BMI). https://www.betterhealth.vic.gov.au/health/healthyliving/body-mass-index-bmi
• The Conversation (Dr Nick Fuller, University of Sydney). 3 signs your diet is causing too much muscle loss, and what to do about it (2024). https://theconversation.com/3-signs-your-diet-is-causing-too-much-muscle-loss-and-what-to-do-about-it-223865
• Eat for Health (NHMRC). Australian dietary guidelines 1 to 5. https://www.eatforhealth.gov.au/guidelines/australian-dietary-guidelines-1-5
• Australian Government Department of Health. Physical activity and exercise guidelines for adults (18 to 64 years). https://www.health.gov.au/topics/physical-activity-and-exercise/physical-activity-and-exercise-guidelines-for-all-australians/for-adults-18-to-64-years

This page is general information only and does not replace individual medical advice. Please speak with a registered Australian healthcare practitioner about your own circumstances.