Body fat calculator
Body fat calculator: the US Navy tape method, explained.
- Fat mass
- 11.9 kg
- Lean mass
- 58.1 kg
- Range, age 20–39
- Healthy (8–19%)
- Typical error
- ± 3.5 points
- BMI
- 22.9
For adults 18 and over. An estimate, not a measurement or medical advice: tape and BMI methods carry an error of several percentage points. Not for use in pregnancy; if you have a medical condition that affects your weight, ask your doctor.
This body fat calculator estimates your body fat percentage from waist, neck and, for women, hip measurements with the US Navy equations, or roughly from your BMI. It shows your fat and lean mass and where the result sits in published healthy ranges, including a set for Asian adults.
- Free, no sign-up
- Centimetres or inches
- Runs in your browser; nothing is saved
How do I calculate my body fat percentage at home?
Measure your waist and neck, and your hips if you are a woman, with a tape measure, then enter them with your height. The US Navy equations turn those into a body fat percentage, with a typical error of about 3.5 points against underwater weighing. Without a tape, a BMI-based formula gives a rougher estimate.
- US Navy equations (Hodgdon and Beckett 1984), in metric and imperial versions
- A BMI-based fallback (Deurenberg 1991), labelled rough
- Fat mass and lean mass in kilograms or pounds
- Healthy ranges by sex and age, with a separate set for Asian adults
How it works
How does this body fat calculator work?
You measure your neck and waist, plus your hips if you are a woman, and enter them with your height, weight, age and sex. The calculator applies the US Navy equations, then works out your fat and lean mass and shows where the result sits in healthy ranges for your age.
Measure your neck
Stand relaxed and wrap the tape just below the Adam’s apple, sloping slightly down towards the front, as in the Navy studies. Keep the tape against the skin without pressing in, and read it as precisely as your tape allows.
- The Navy studies recorded each measurement to the nearest millimetre
- Measure two or three times and use the average
Measure your waist
Men measure around the abdomen at the level of the navel. Women measure the natural waist, the narrowest point between the bottom of the breastbone and the navel. Stand relaxed, keep the tape level, and read it at the end of a normal breath out.
- Men: at the navel
- Women: the narrowest point above the navel
Women: measure your hips
Women also measure around the hips at the level where the buttocks stick out most, with the tape level. The women’s equation adds waist and hip and subtracts the neck: that combination predicted body fat best in the Navy’s study of women.
- The men’s equation uses waist minus neck
- Both equations also use height
Read the result
The calculator applies the Navy equation for your units, then splits your weight into fat mass and lean mass. It shows where the result falls in Gallagher’s healthy ranges for your sex and age, using the set for white and African American adults or the set for Asian adults.
- Typical error: about 3.5 points for men and 3.7 for women
- Measure at the same time of day, in the same way, each time
Formulas
What are the US Navy body fat formulas?
The original Navy equations predict body density from the logarithms of circumferences and height in centimetres, and Siri’s equation turns density into percent fat. For the Department of Defense they were refitted to give percent fat directly from inches. The versions give almost the same answer, so each is used with its own units.
D = 1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)D = 1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)BF = 495 ÷ D − 450BF = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387BF = 1.20 × BMI + 0.23 × age − 10.8 × S − 5.4FM = W × BF ÷ 100; LM = W − FM- D: body density in g/ml; BF: body fat in percent
- Metric: circumferences and height in cm; imperial: in inches
- log10: the base-10 logarithm
- BMI: weight in kg ÷ (height in m)²; S: 1 for men, 0 for women; age in years
- W: body weight; FM: fat mass; LM: lean (fat-free) mass
Healthy ranges
What is a healthy body fat percentage?
Gallagher and colleagues noted that no accepted ranges existed, and proposed provisional ones by matching body fat to the BMI cut-offs of 18.5, 25 and 30. For white and African American adults aged 20 to 39, the healthy range is 8 to 19% for men and 21 to 32% for women. Asian ranges start higher.
| Sex, age and sample | Below healthy | Healthy | Overweight | Obese |
|---|---|---|---|---|
| Men 20–39, white or African American | Under 8% | 8–19% | 20–24% | 25% or more |
| Men 40–59, white or African American | Under 11% | 11–21% | 22–27% | 28% or more |
| Men 60–79, white or African American | Under 13% | 13–24% | 25–29% | 30% or more |
| Women 20–39, white or African American | Under 21% | 21–32% | 33–38% | 39% or more |
| Women 40–59, white or African American | Under 23% | 23–33% | 34–39% | 40% or more |
| Women 60–79, white or African American | Under 24% | 24–35% | 36–41% | 42% or more |
| Men 20–39, Asian | Under 13% | 13–22% | 23–27% | 28% or more |
| Men 40–59, Asian | Under 13% | 13–23% | 24–28% | 29% or more |
| Men 60–79, Asian | Under 14% | 14–23% | 24–28% | 29% or more |
| Women 20–39, Asian | Under 25% | 25–34% | 35–39% | 40% or more |
| Women 40–59, Asian | Under 25% | 25–34% | 35–40% | 41% or more |
| Women 60–79, Asian | Under 25% | 25–35% | 36–40% | 41% or more |
Source: Gallagher et al. (2000), Tables 4 and 5: body fat predicted at BMI 18.5, 25 and 30, rounded to whole percent. The Asian sample was Japanese adults. The authors called the ranges provisional.
Worked example
What does a worked example look like?
Take a man 175 cm tall with an 85 cm waist and a 38 cm neck. The Navy equation gives a density of 1.0324 − 0.19077 × log10(47) + 0.15456 × log10(175) = 1.0601, and Siri’s equation 495 ÷ 1.0601 − 450 = 16.9% body fat. At 70 kg that is 11.9 kg of fat.
- His lean mass is 70 − 11.9 = 58.1 kg; at 30 he is in the healthy range for his age, 8–19%
- The same man measured in inches gets 17.0% from the imperial equation, 0.1 points more
- A woman 165 cm tall with a 75 cm waist, 100 cm hips and a 33 cm neck: density 1.0325, body fat 29.4%
- The BMI route for the man at 30: 1.20 × 22.86 + 0.23 × 30 − 10.8 − 5.4 = 18.1%
Asian and Indian adults
Do the results apply to Asian and Indian people?
With care. At the same BMI, the Asian groups studied, including Singaporean Indians, carried about 3 to 5 percentage points more body fat than white people. A WHO expert consultation found many Asian people at high risk of diabetes and heart disease below BMI 25, and an Indian consensus set lower normal BMI limits.
- The BMI formula comes from a Dutch study, so for Asian and Indian users it likely reads low
- Gallagher’s Asian ranges come from Japanese adults; that paper has no Indian set
- In a 1999 Defense Department review, race had no meaningful effect on the Navy equations’ predictions
- WHO suggested extra public health action points at BMI 23, 27.5, 32.5 and 37.5 for Asian populations
Accuracy
How accurate is the US Navy method?
In the original studies the equations predicted underwater-weighing results with a standard error of 3.5 points for 602 men and 3.7 points for women. Checked on other groups, the errors were 2.7 points for men and 4.0 to 4.4 points for women. Your taping adds error of its own, so measure carefully.
- The equations come from US Navy personnel; Gallagher’s ranges from adults in the UK, US and Japan
- The BMI formula’s error is larger, 4.1 points, and it slightly overestimates body fat in obesity
- BMI cannot tell muscle from fat, so it misreads very muscular people
- Gallagher found differences between methods and even machines, so compare results from one method
Using it
How should I use my body fat result?
Use it as a starting point and follow the trend. Measure the same way every few weeks, at the same time of day, and see whether your waist and the estimate move the way you expect. One reading can be off because of how the tape sat, so judge by several readings over time.
- Your body fat figure lets the TDEE calculator use the Katch-McArdle equation
- Lean mass is what some protein advice for lean athletes is based on
- Recalculate after a real change in weight or waist
Limits
Who should not use this body fat calculator?
It is for adults. Do not rely on it if you are under 18 or pregnant, or if you have a medical condition that changes your weight or shape. The ranges cover ages 20 to 79 only. For a medical assessment of body fat, ask your doctor about a measured method such as DXA.
- Under 18: the Deurenberg study found children need a different formula
- Pregnancy changes waist and hip measurements, so the tape method does not apply
- Below 20 or from 80, the calculator gives the estimate without a range
For coaches
How do coaches track body fat with their clients?
Track the tape measurements themselves, and use an estimate like this one as context. In Trainaq the intake form and weekly check-ins can ask for weight, waist, hip, neck and body fat among nine measurements, in metric or imperial units, and the progress view shows the latest of each.
- The intake sets each client’s starting measurements
- Each check-in adds weight and any measurements you ask for
- You see the weight trend and latest measurements in Trainaq Coach and on the web
Sources
Sources
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men from body circumferences and height. Report No. 84-11. San Diego: Naval Health Research Center; 1984.
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy women from body circumferences and height. Report No. 84-29. San Diego: Naval Health Research Center; 1984.
- Hodgdon JA, Friedl K. Development of the DoD body composition estimation equations. Technical Document No. 99-2B. San Diego: Naval Health Research Center; 1999.
- Deurenberg P, Weststrate JA, Seidell JC. Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. Br J Nutr. 1991;65(2):105–114.
- Gallagher D, Heymsfield SB, Heo M, 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.
- WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet. 2004;363(9403):157–163.
- Deurenberg P, Deurenberg-Yap M, Guricci S. Asians are different from Caucasians and from each other in their body mass index/body fat per cent relationship. Obes Rev. 2002;3(3):141–146.
- Misra A, Chowbey P, Makkar BM, et al. Consensus statement for diagnosis of obesity, abdominal obesity and the metabolic syndrome for Asian Indians and recommendations for physical activity, medical and surgical management. J Assoc Physicians India. 2009;57:163–170.
FAQ
Body fat calculator FAQ
Why does my smart scale give a different body fat number?
Each method estimates body fat in its own way and carries its own error. Most smart scales use a small electrical current through your body, the tape method uses your shape, and the BMI route uses only weight and height. Gallagher’s team found differences between methods and machines, so compare readings from one method.
Is the tape method better than BMI for estimating body fat?
Usually, yes. In their own studies the Navy equations had a smaller standard error than the BMI formula, about 3.5 points against 4.1, and they use your waist instead of weight alone. BMI cannot separate muscle from fat, so very muscular people get a misleadingly high estimate from it.
Do women use the same formula as men?
No. Women have their own Navy equation, which adds hip circumference to the waist before subtracting the neck, the combination that predicted body fat best in the Navy’s study of women. Healthy ranges differ too: in Gallagher’s tables, women’s ranges sit about 11 to 14 points higher than men’s of the same age.
What is lean body mass?
Lean body mass, or fat-free mass, is everything in your body that is not fat: muscle, bone, organs and water. The calculator finds it by subtracting your fat mass from your weight. The Katch-McArdle equation in the TDEE calculator uses it, and some protein advice for lean athletes is set per kilogram of it.
How often should I measure my body fat?
Every few weeks is enough for most people, because the estimate moves slowly and one reading can be off by how the tape sat. Measure at the same time of day, in the same conditions and with the same tape, then look at the trend across several readings instead of any single number.
