Body fat calculator
Measure your neck, waist and height (plus hip for women) to estimate your body fat with the US Navy method. It is an estimate, not a lab result.
Filled in with example values. Replace them with yours.
Standing straight, without shoes.
Just below the larynx, tape sloping slightly down to the front.
At the navel, relaxed, breathing out. Do not pull your stomach in.
Around the widest point of the buttocks, feet together.
Adds fat mass and lean mass to the result.
Estimated body fat
ACE category: Fitness
- Fat mass
- 12.6 kg
- Lean mass
- 65.4 kg
Circumference methods are typically within a few percentage points of lab methods. For one person the error can be larger, so watch the trend more than a single reading.
Work out your calorie needs →| Category | Body fat |
|---|---|
| Essential fat | 2–5 % |
| Athletes | 6–13 % |
| Fitness | 14–17 % |
| Average | 18–24 % |
| Obese | 25+ % |
These ranges describe, they do not diagnose or set a goal. A healthy level depends on age, sport and build.
How the calculator works
The calculator uses the US Navy method, developed by Hodgdon and Beckett at the Naval Health Research Center in 1984. It estimates body fat from three tape measurements and your height, with one equation for men and one for women. In centimeters:
Men: body fat % = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
Women: body fat % = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
The equations were fitted by comparing the circumferences of service members with their body density from underwater weighing. The result is a statistical relationship: people with a larger waist relative to their neck and height tend to carry more fat. If you enter inches, the calculator converts them to centimeters first. For the example above (180 cm, neck 38 cm, waist 85 cm) the equation gives 16.1 %.
Why circumferences at all? A tape costs very little and works anywhere. Lab methods measure more directly, but they need a machine, an appointment and money. The Navy method trades some accuracy for something you can repeat at home.
How to measure
Good measurements matter more than any other part of this page. A one-centimeter slip at the waist moves the result by roughly half a point or more, so take your time.
- Use a flexible tape that does not stretch, on bare skin or over thin clothing.
- Measure at the same time of day, ideally in the morning before eating, with a relaxed body.
- Neck: just below the larynx (the Adam’s apple), the tape sloping slightly down toward the front. Keep your shoulders down and do not flare your neck.
- Waist: for men at the navel, for women at the narrowest point of the torso (at the navel if there is no clear narrowing). Stand relaxed, breathe out normally and do not pull your stomach in.
- Hip (women): around the widest point of the buttocks, feet together.
- Snug, not tight: the tape lies flat against the skin without pressing in.
- Measure three times for each site and enter the average. If two readings differ by more than a centimeter, measure again.
How accurate is it?
The Navy equations were built to be within a few percentage points of underwater weighing, and tape methods are typically within a few percentage points of lab methods. That is good enough to place yourself in a range, but it is not exact.
For a single person the error can be larger. In one small study of 23 male R.O.T.C. cadets, the Army’s circumference equation (a related tape method) generally gave lower body fat than DXA, and 13 of the 23 results fell outside a zone of agreement of 2 to 4 points of body fat (Mitchell 2017). The equation also fits some body types worse than others: very muscular people, or people who store fat unusually, can be over- or under-estimated.
How does it compare with other methods you may have at hand?
- DXA scan: a low-dose X-ray scan, commonly used as a reference in studies. More direct, but it also has its own error and you need an appointment.
- Skinfold calipers: accurate in trained hands, unreliable if the person measuring changes or lacks practice.
- Smart scales and other impedance devices: convenient, but the reading moves with hydration, a recent meal and the time of day.
None of them is perfect. What helps most is consistency: the same method, the same time of day, and a trend over weeks.
Body fat percentage chart for men and women
The table beside the calculator shows the ranges for your sex. They are the categories of the American Council on Exercise (ACE):
- Essential fat: men 2–5 %, women 10–13 %
- Athletes: men 6–13 %, women 14–20 %
- Fitness: men 14–17 %, women 21–24 %
- Average: men 18–24 %, women 25–31 %
- Obese: men 25 % and above, women 32 % and above
What the number means
Essential fat is the minimum the body needs to work normally, and it is not a target. The categories are rough descriptions of groups of adults. They do not diagnose anything, and they say nothing about your fitness, your strength or your health on their own.
Women carry more essential fat than men, which is why their ranges sit higher. Body fat also tends to rise with age, and many athletes sit in different ranges for good reasons. Health is more than one number: sleep, activity, strength, blood values and how you feel all count.
Fat mass and lean mass
If you enter your body weight, the calculator splits it in two. Fat mass is your weight times the body fat percentage. Lean mass is the rest: muscle, bone, organs and water. A person at 78 kg and 16.1 % has about 12.6 kg of fat and 65.4 kg of lean mass.
The split is useful when the scale does not move. If your weight stays the same while your waist gets smaller, you may be losing fat and gaining muscle. Because the numbers come from an estimate, treat small changes of a kilogram with care.
Tracking the trend
Do not measure every day. Body fat changes slowly, day-to-day water shifts are larger than real change, and the error of a single reading is bigger than a week of progress. Every 2 to 4 weeks is a good rhythm. Use the same tape, the same spots and the same time of day, and write the numbers down.
If your waist shrinks and your strength holds or grows, you are on a good track, whatever the exact percentage says. If you are training for muscle, a rising weight with a stable waist is also a good sign.
Body measurements in Muscla
Muscla tracks your weight trend and your progress next to your workouts, so you can see how your body and your lifts change together. Use this calculator whenever you want a rough body fat estimate, and read it alongside your weight, your strength and how you feel.
Coming to the App Store. Free to start.
Questions
How accurate is the US Navy body fat method?
It is typically within a few percentage points of laboratory methods such as underwater weighing, which is good enough to see where you stand, but not to split hairs. For one person the error can be larger, and a study of 23 cadets found the related Army tape equation mostly underestimated body fat compared with DXA. Use it to follow your own trend.
Why is my neck measurement part of the formula?
The formula uses the difference between waist and neck as a stand-in for fat around the middle, because the neck reflects frame size and muscle in the upper body. Height sets the scale. It is a statistical shortcut built from measurements of many people, not a direct look at your fat.
Why do women need a hip measurement?
Women store fat differently, more around the hips. The original researchers fitted a separate equation for women that uses waist, hip, neck and height. That is why the hip field appears when you choose female.
How often should I measure?
Every 2 to 4 weeks is enough. Body fat changes slowly, and the measurement error is larger than a week of change. Measure at the same time of day, with the same tape, and compare like with like.
Is it better than a smart scale?
Neither is a lab method. Smart scales send a weak electrical current through the body, and their result moves with hydration, food and time of day. A tape measure does not depend on water, but it depends on how carefully you place it. Whichever you choose, use the same one every time.
What is a healthy body fat percentage?
It depends on age, sex, sport and build, and a single number cannot say whether you are healthy. The ACE ranges are a common reference for adults: they describe typical groups of people. If you are worried about your health, a doctor can look at more than body fat, such as blood pressure, blood values and fitness.
Sources
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men from body circumferences and height. Naval Health Research Center, San Diego, CA. Report No. 84-11. 1984.
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy women from body circumferences and height. Naval Health Research Center, San Diego, CA. Report No. 84-29. 1984.
- U.S. Department of Defense. DoD Instruction 1308.03: DoD Physical Fitness and Body Composition Program (circumference equations in inches).
- American Council on Exercise. What are the guidelines for percentage of body fat loss? ACE Ask the Expert. 2009.
- Mitchell KM, Pritchett RC, Gee DL, Pritchett KL. Comparison of circumference measures and height-weight tables with dual-energy X-ray absorptiometry assessment of body composition in R.O.T.C. cadets. Journal of Strength and Conditioning Research. 2017;31(9):2552-2556.