Women's Health
Women’s Body Fat Calculator
This calculator estimates your body fat percentage from four tape measurements: height, neck, natural waist and hips. It uses the US Navy's equation for women, developed in the 1980s by comparing tape measurements with underwater weighing. You can enter centimetres or inches, and add your age and weight if you'd like more context.
Your result is an estimate with a margin of about 4 percentage points either way. You'll see where it falls on the American Council on Exercise (ACE) chart, how it compares with age-based reference levels from a 2000 study, and, if you add your weight, roughly how much of you is fat and how much is lean mass. It can't diagnose anything, and there is no single "normal" body fat number that suits everyone.
Your measurements
Without shoes, standing straight with your back against a wall.
Your natural waist: the narrowest point, usually about halfway between your belly button and the bottom of your breastbone. Measure after a normal breath out.
Around the fullest part of your bottom, with the tape level all the way round.
Just below your voice box, looking straight ahead with relaxed shoulders. Keep the tape as level as you can.
Optional. Adds age-based reference levels. It does not change your result.
Optional. Used only to split your weight into fat mass and lean mass.
Estimated body fat
28.9%
Acceptable range (25–31%)
This is within the range ACE lists as acceptable.
Likely range: about 25% to 33%. The equation's standard error is 3.7 percentage points (IOM 1998), so read your result as a band, not an exact figure.
How the US Navy body fat method works for women
The US Navy method estimates body fat from the size of a few body parts rather than from a scan. For women it uses four numbers: height, neck, natural waist and hips. It adds the waist and hip measurements, subtracts the neck, and puts that figure and your height into an equation that predicts body density. A standard formula (the Siri equation) then turns density into a body fat percentage.
The women's equation comes from a 1984 Naval Health Research Center report by Hodgdon and Beckett. The researchers measured Navy women with a tape and also weighed them underwater, the reference method of the time, and built an equation from the tape measurements that predicted the underwater result. A 1998 Institute of Medicine report lists the equation with a correlation of 0.85 and a standard error of 3.7 percentage points.
Why the hips? The US military's Human Performance Resources Center (HPRC) explains that the women's standards reflect typical female fat distribution, covering pear and hourglass shapes with narrower waists as well as apple shapes with larger waists.
The method was designed as a quick field method for military body composition checks. That makes it handy at home: all you need is a flexible tape measure. It also means the result is an estimate of the kind a group screening uses, not a lab measurement.
How to measure your neck, waist and hips
Small changes in where the tape sits matter: with the default numbers, a waist 2 cm larger moves the result up by about 1 percentage point. So it's worth following one routine every time. These steps follow the US Navy's measuring guide.
- Use a flexible tape that doesn't stretch. Wear light clothing or measure on bare skin.
- Stand up straight, feet together, arms relaxed at your sides, looking straight ahead.
- Neck: place the tape just below your voice box (larynx), not over it. Look straight ahead with your shoulders down and relaxed, and keep the tape as level as you can.
- Natural waist: find the narrowest part of your middle, usually about halfway between your belly button and the bottom of your breastbone. Measure at the end of a normal, relaxed breath out. Don't pull your stomach in.
- Hips: measure around the fullest part of your bottom, with the tape level all the way round.
- Height: stand without shoes, straight but not stiff, looking directly ahead.
- Snug, not tight: the tape should touch your skin all the way round without pressing in.
- Repeat: take each measurement twice, going round neck, waist and hips in turn. If two readings differ by more than about 2.5 cm (1 inch), take a third and average the two closest.
The Navy's guide also rounds each measurement to the nearest half inch, rounding the neck up and the waist and hips down, before looking up a table. This calculator uses your exact numbers, so its answer can differ from an official Navy table by about a point.
Pick a consistent time, such as first thing in the morning before eating, so changes you see later reflect your body rather than your breakfast.
What your body fat percentage means
There is no single agreed "normal" body fat percentage. Harvard Health says plainly that there is no agreed-upon normal range for body fat, just as there is no ideal body weight. So this calculator shows two different references and explains where each comes from.
The ACE chart. The American Council on Exercise publishes body fat norms that many fitness professionals use:
| Your result | ACE description for women |
|---|---|
| 10–13% | Essential fat |
| 14–20% | Athletes |
| 21–24% | Fitness |
| 25–31% | Acceptable |
| 32% and above | Above acceptable (ACE's chart calls this obesity) |
ACE prints whole numbers with gaps between rows, for example "Acceptable 25–31%" and "Obesity >32%". This calculator treats each row as running up to the start of the next, so 31.9% counts as acceptable and 32.0% or more as above acceptable. Your result is rounded to one decimal place first, and the label always matches the number you see.
Age-based levels (optional). A 2000 study by Gallagher and colleagues, published in the American Journal of Clinical Nutrition, measured body fat with a detailed lab method in 1,626 adults and worked out which body fat levels matched the standard BMI cut-offs. For women it found:
| Age | Body fat linked to BMI 18.5 | BMI 25 | BMI 30 |
|---|---|---|---|
| 20–39 | 21% | 33% | 39% |
| 40–59 | 23% | 34% | 40% |
| 60–79 | 24% | 36% | 42% |
The authors called these provisional healthy ranges. They come from white and African American adults; Asian participants had more body fat at the same BMI, so these levels may read low for Asian women. The table doesn't cover women under 20 or over 79, so no age row appears for those ages.
Another recent view. A study published in 2024, using US national survey data, linked body fat to metabolic syndrome. In women it found no cases below 30% body fat and proposed 36% as the equivalent of "overweight" and 42% as "obesity". That study used DXA scans, which read differently from a tape estimate, so treat these as context rather than a target.
How accurate is a tape-measure body fat estimate?
The equation's standard error is 3.7 percentage points. In plain words, if your result is 29%, your true level is more likely to be somewhere around 25% to 33% than exactly 29%. That's why the calculator shows a "likely range" of about 4 points either side. It is not a guaranteed range: some people will be further out.
The 3.7-point figure comes from the original Navy group. Outside that group, accuracy can be lower:
- Middle-aged women. A 1995 study tested the equation in 62 women aged 40 to 60. On average it came close to underwater weighing (30.3% versus 29.5%), but individual results varied, and the authors advised caution when using it for one person.
- Strong glutes. HPRC notes that measuring around the widest part of the hips includes the gluteal muscles, so bigger glutes from strength training can lead to overestimating body fat.
- Very lean or very high results. In a 2022 study of US Marines, a waist-based tape method tended to overestimate lean people and underestimate people with more body fat when compared with DXA scans.
The most useful way to read your number is as a trend. If you measure the same way each time, a drop from 33% to 30% over a few months is more meaningful than whether a single reading says 30% or 31%.
If you need a precise figure, for example for a medical reason, ask a doctor about a DXA scan or another lab method. Harvard's Nutrition Source notes that DXA is accurate but is typically used in research settings.
Fat mass and lean mass
If you enter your weight, the calculator splits it into two parts:
- Fat mass = weight × body fat percentage ÷ 100.
- Lean mass = weight − fat mass. This is everything that isn't fat: muscle, bone, organs and water.
Worked example. A woman who weighs 70 kg with a result of 28.9% has about 70 × 0.289 = 20.2 kg of fat mass and 70 − 20.2 = 49.8 kg of lean mass.
These numbers inherit the same uncertainty as the percentage. A 4-point error on 70 kg is about 2.8 kg of fat, so read fat mass as "roughly 17 to 23 kg" rather than an exact figure.
Why bother? Weight alone can hide what's changing. If you start strength training, your weight might stay the same while your waist shrinks and your lean mass rises. Harvard Health notes that regular strength training can add muscle mass, which is healthy, and that staying at the same weight while your waist grows can point to fat gain or muscle loss. Tracking fat and lean mass together, with the same tape and the same routine, gives a fuller picture than the scale alone.
Body fat percentage vs BMI vs waist measures
| Measure | What it uses | What it's good for | Main limits |
|---|---|---|---|
| Body fat % (this calculator) | Height, neck, waist, hips | Estimating how much of your weight is fat | About ±4 points; depends on tape placement |
| BMI | Height and weight | Quick screening; widely used by doctors | Can't tell fat from muscle |
| Waist size | Waist only | Belly fat and heart and diabetes risk | Doesn't account for height or frame |
| Waist-to-height ratio | Waist and height | Simple risk screen for belly fat | Says nothing about total body fat |
| Waist-to-hip ratio | Waist and hips | Where you carry fat (apple vs pear) | A ratio, not a fat amount |
BMI's main limit is that it doesn't account for body composition. HPRC explains that people with the same BMI can have very different body fat depending on sex, race, age and fitness, and that BMI tends to label short, muscular people as overweight. HPRC also notes BMI is fairly accurate as a body fat guide at values over 30.
Waist measures add something body fat percentage doesn't: where the fat sits. Harvard Health notes that a waist of 35 inches (about 89 cm) or more in women raises the risk of heart disease and type 2 diabetes. It suggests using more than one measure and tracking them over time instead of relying on one number. Our waist-to-hip ratio calculator works from the same tape measurements.
Body fat at different life stages
Periods. Very low body fat can be linked with missed periods. The NHS lists sudden weight loss, too much exercise and stress among the common causes of stopped or missed periods, along with being overweight. The International Olympic Committee's 2023 statement on relative energy deficiency in sport (REDs) links low energy availability to effects on health and performance, and includes guidelines for safe and careful body composition assessment in athletes. The NHS advises seeing a GP if you've missed your period 3 times in a row, whatever this calculator says.
PCOS. The NHS now calls this condition polyendocrine metabolic ovarian syndrome (PMOS). A 2021 review of imaging studies found that women with polycystic ovary syndrome tended to carry more abdominal fat than women of the same BMI without it. Results from MRI and CT scans, however, showed similar fat distribution, so the link isn't settled. A tape estimate can't diagnose PCOS or rule it out.
Pregnancy and after birth. This calculator isn't for use during pregnancy. The Navy's own guide exempts pregnant and postpartum Sailors from body composition assessment. After birth, the body's water balance takes time to settle: a 2022 review describes one study where standard body fat methods gave significant errors at 2 weeks after birth, and another where the pregnancy changes in body water were no longer seen by 3 months. Wait a few months before reading much into a result.
Menopause. The US SWAN study followed women through the menopause transition. At its start, the rate of fat gain doubled and lean mass began to decline, and these changes continued until about 2 years after the final period before levelling off. A large US survey using DXA found that women's median body fat percentage peaked at around age 65. So a gradual rise in midlife is common, and age-based reference levels (see the age table above) can help put your number in context.
What to do with your result
- Treat it as a starting point. Use the likely range, not just the single number.
- Track the trend. Measure every few weeks at the same time of day, with the same tape and the same routine.
- Look at your waist too. Body fat and waist size together tell you more than either alone.
- Don't aim for the lowest number. Body fat below ACE's essential range isn't a goal. Sudden weight loss and too much exercise are common causes of missed periods, and low energy availability can harm athletes' health and performance.
- Talk to a doctor if you're worried about your weight, your periods have changed, or you want a precise measurement such as a DXA scan.
- Skip it if it isn't helping. If tracking body numbers makes you anxious or feeds worries about eating, it's fine to stop and talk to someone you trust or a doctor.
Frequently asked questions
There's no single agreed healthy number. ACE lists 25–31% as acceptable and 21–24% as fitness for women. A 2000 study linked about 21–33% at ages 20–39, 23–34% at 40–59 and 24–36% at 60–79 to a healthy BMI. Your health also depends on where you carry fat, your activity and other factors.
It's a reasonable estimate, not a precise measurement. In the original Navy study its standard error was 3.7 percentage points, so a result of 29% usually means somewhere around 25% to 33%. Accuracy can be lower for some women, for example those with very muscular glutes or results at the extremes.
Because women often carry fat differently from men. HPRC says the women's tape standards are based on typical female fat distribution, covering pear and hourglass shapes with narrower waists as well as apple shapes with bigger waists. Including the hips lets the equation reflect those different shapes.
Measure your natural waist: the narrowest part of your middle, usually about halfway between your belly button and the bottom of your breastbone. Stand straight, breathe out normally, and keep the tape level and snug without pressing in. This differs from the belly-button measurement the Navy uses for men.
Use whichever matches your tape. The switch converts inches to centimetres exactly (1 inch is 2.54 cm) before the calculation, so you get the same result either way. Just make sure the switch matches how you measured. The calculator flags numbers that look like inches typed into the centimetre boxes.
Each method estimates body fat in a different way, and none of them is exact. Home scales use a small electric current, which Harvard's Nutrition Source notes can be affected by hydration and illness. A tape estimate depends on placement. Differences of several points between methods are common, so compare like with like.
Not necessarily. On the ACE chart, 30% sits in the acceptable range (25–31%) for women. In the 2000 Gallagher study, 30% fell within the levels linked to a healthy BMI for women aged 20 to 79. A 2024 study found no metabolic syndrome cases below 30% body fat in women.
Essential fat is the minimum your body needs to work normally. ACE lists 10–13% as essential fat for women. Very low body fat isn't a goal: the NHS lists sudden weight loss and too much exercise among common causes of missed periods. If your result is very low, or you've missed periods, it's worth talking to a doctor.
Yes. Body fat usually rises with age, partly because muscle mass tends to fall. A large US survey using DXA scans found women's median body fat percentage peaked at around age 65. That's why age-based reference levels are a little higher for older women. Add your age to see them.
Multiply your weight by your body fat percentage and divide by 100 to get fat mass. Subtract that from your weight to get lean mass. For example, 70 kg at 28.9% is about 20.2 kg of fat and 49.8 kg of lean mass. Enter your weight and the calculator does this for you.
It answers a different question. BMI uses only height and weight, so it can't tell fat from muscle and may label muscular people as overweight. Body fat percentage estimates how much of your weight is fat but is less precise. Using both, with a waist measurement, gives a fuller picture than either alone.
It isn't designed for pregnancy, and the results won't be meaningful while you're pregnant. The US Navy exempts pregnant and postpartum women from its body fat checks. After birth, body water takes time to settle, so wait a few months, and ask your midwife or doctor if you have concerns. Try our Pregnancy Weight Gain Calculator to see a typical weight-gain range for your pregnancy.
Often, yes. The US SWAN study found that at the start of the menopause transition, the rate of fat gain doubled and lean mass started to fall, with changes continuing until about 2 years after the final period. A gradual midlife rise is common, and regular strength training can help build muscle. Try our Menopause Age Calculator to estimate when menopause may start for you.
It may affect where fat is stored. A 2021 review found women with polycystic ovary syndrome tended to carry more abdominal fat than women of the same BMI without it, though MRI and CT results were mixed. This calculator can't diagnose or rule out PCOS. Talk to a doctor if you have symptoms. Try our Waist-to-Hip Ratio Calculator to see how your fat is spread between waist and hips.
Military rules have been changing. The Navy's February 2025 guide used tape measurements as one step, with a 36% maximum for women. HPRC says that from January 1, 2026, the military uses waist-to-height ratio to assess body composition. If you're preparing for a service test, check your branch's current guidance.
Sources
- Institute of Medicine. Assessing Readiness in Military Women: The Relationship of Body Composition, Nutrition, and Health (1998), Appendix B, Table B-2.
- US Navy. Physical Readiness Program Guide 4: Body Composition Assessment (February 2025), archived copy.
- Human Performance Resources Center (HPRC), How the military measures body composition.
- American Council on Exercise, Percent Body Fat Calculator (body fat norms table), archived copy.
- Gallagher D, et al. Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index. Am J Clin Nutr 2000;72(3):694–701. (abstract and Table 4 read from an archived copy of the journal page)
- Bathalon GP, et al. Military body fat standards and equations applied to middle-aged women. Med Sci Sports Exerc 1995;27(7):1079–1085. (abstract only)
- Potter AW, et al. Defining overweight and obesity by percent body fat instead of body mass index. J Clin Endocrinol Metab (published online 2024).
- Potter AW, et al. Circumference-based predictions of body fat revisited: preliminary results from a US Marine Corps body composition survey. Front Physiol 2022.
- Kelly TL, Wilson KE, Heymsfield SB. Dual energy X-ray absorptiometry body composition reference values from NHANES. PLoS One 2009.
- Greendale GA, et al. Changes in body composition and weight during the menopause transition (SWAN). JCI Insight 2019.
- Imaging-based body fat distribution in polycystic ovary syndrome: a systematic review and meta-analysis. Front Endocrinol 2021.
- Beyond the BMI: validity and practicality of postpartum body composition assessment methods during lactation: a scoping review. Nutrients 2022.
- Mountjoy M, et al. 2023 International Olympic Committee's (IOC) consensus statement on relative energy deficiency in sport (REDs). Br J Sports Med 2023. (abstract only)
- Harvard Health Publishing, What is considered a healthy body fat percentage as you age?
- Harvard T.H. Chan School of Public Health, The Nutrition Source: Measuring body fat.
- NHS, Stopped or missed periods.