Free calculator
Body Fat Calculator (US Navy Method)
Written by the GymStreak coaching teamUpdated
Just below the Adam's apple, tape sloping slightly down at the front.
Level with your navel, standing relaxed, without pulling your stomach in.
Adds your fat mass and lean mass.
The short answer
You can estimate your body fat percentage with a tape measure using the US Navy method: it plugs your height, neck and waist (plus hips for women) into equations developed by Hodgdon and Beckett in 1984. For example, a man who is 180 cm tall with a 38 cm neck and a 90 cm waist comes out at about 19.8% body fat. Expect the estimate to be a few percentage points off a lab scan, so use it to track change over time.
01 / How it works
How the body fat calculator works
Most body fat sits around the trunk, so a bigger waist relative to your neck and height usually means more fat. In the early 1980s researchers at the US Naval Health Research Center measured sailors' circumferences, compared them with body fat measured by underwater weighing, and turned the relationship into two equations: one for men using the waist and neck, and one for women that adds the hips. For decades they were the standard US military tape test.
Enter your sex, height and measurements in centimetres or inches. Inches are converted to centimetres first and everything runs through the metric version of the equations, so both units give the same answer. Add your body weight if you want to see how many kilograms or pounds of that are fat and how many are lean mass (muscle, bone, organs and water).
The result is placed in the body fat categories published by the American Council on Exercise (ACE). How you measure matters more than anything else: a 1 cm error at the waist moves the result by roughly half to three-quarters of a percentage point, so measure the same way every time.
02 / Formula
The body fat formulas
US Navy body fat equation (men), centimetres
%BF = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
- waist = abdomen at navel level, in cm
- neck = just below the larynx, in cm
- height in cm
- log10 = base-10 logarithm
The "495 ÷ … − 450" part is the Siri equation, which turns an estimated body density into a body fat percentage. This is the version the calculator runs.
Source: Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men from body circumferences and height. Naval Health Research Center Report No. 84-11; 1984.
US Navy body fat equation (women), centimetres
%BF = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
- waist = narrowest point of the natural waist, in cm
- hip = widest point of the buttocks, in cm
- neck and height as for men
Source: Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy women from body circumferences and height. Naval Health Research Center Report No. 84-29; 1984.
The same equations in inches (US military form)
Men: %BF = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76 Women: %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
- all measurements in inches
This is how the equations appear in US Army regulation AR 600-9. It gives almost the same answer as the centimetre form (usually within a few tenths of a percent), so the calculator converts inches to centimetres rather than switching formula.
03 / Worked example
Worked examples
A man: 180 cm, neck 38 cm, waist 90 cm, 80 kg
He measures his neck just below the Adam's apple and his waist level with his navel.
- 1waist − neck = 90 − 38 = 52 cm
- 2log10(52) = 1.7160 · log10(180) = 2.2553
- 31.0324 − 0.19077 × 1.7160 + 0.15456 × 2.2553 = 1.0536
- 4%BF = 495 ÷ 1.0536 − 450 = 19.8%
- 5Fat mass = 80 × 0.198 = 15.8 kg · Lean mass = 64.2 kg
About 19.8% body fat, in ACE's "average" range for men (18–24%). If his waist dropped to 85 cm with everything else the same, the estimate would fall to about 16.1%.
A woman: 165 cm, neck 32 cm, waist 72 cm, hips 98 cm
She measures her waist at its narrowest point and her hips at the widest part of the buttocks.
- 1waist + hip − neck = 72 + 98 − 32 = 138 cm
- 2log10(138) = 2.1399 · log10(165) = 2.2175
- 31.29579 − 0.35004 × 2.1399 + 0.22100 × 2.2175 = 1.0368
- 4%BF = 495 ÷ 1.0368 − 450 = 27.4%
About 27.4% body fat, in ACE's "average" range for women (25–31%).
The inch form: 5 ft 10 in, neck 15 in, waist 34 in (man)
The same method with measurements taken in inches.
- 1Height = 70 in · waist − neck = 34 − 15 = 19 in
- 286.010 × log10(19) = 86.010 × 1.2788 = 109.99
- 370.041 × log10(70) = 70.041 × 1.8451 = 129.23
- 4%BF = 109.99 − 129.23 + 36.76 = 17.5%
About 17.5%. Converting to centimetres and using the metric form gives 17.4%, which is what the calculator shows.
04 / Reference
Body fat charts and tables
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25% and above | 32% and above |
Women carry more essential fat than men, which is why every band is higher. These are general categories, not medical cut-offs.
Source: American Council on Exercise (ACE). Percent body fat categories.
| Measurement | Where | Tips |
|---|---|---|
| Neck | Just below the larynx (Adam's apple) | Tape sloping slightly down to the front; do not flare the neck |
| Waist (men) | Around the abdomen, level with the navel | Stand relaxed; do not pull your stomach in |
| Waist (women) | Narrowest point of the natural waist | Usually about halfway between navel and breastbone |
| Hips (women) | Widest part of the buttocks | Feet together, tape level all the way round |
| Height | Barefoot, standing tall against a wall | Measure once; it does not change |
Measure in the morning before eating, with the tape snug but not pressing into the skin, and take the average of two or three readings.
Source: US Army. AR 600-9, The Army Body Composition Program. 2013. Appendix B (circumference measurement).
05 / Training
How to use your body fat estimate
- Track the trend, not one reading. Re-measure every two to four weeks at the same time of day. If your waist is going down while your strength holds, you are losing fat.
- To lose fat, eat a little less and keep lifting. Set a calorie target with the TDEE calculator and a protein target with the macro calculator. How to eat and work out for healthy, sustainable fat loss covers the basics.
- Build muscle with compound lifts. More lean mass at the same weight lowers your body fat percentage. Start with barbell squats, the barbell deadlift, bent over rows and pushups.
- You cannot choose where the fat comes off. Ab exercises do not burn belly fat on their own; see stubborn fat: what's the deal?.
- Wondering how lean is healthy? Very low body fat has real costs. Read what's a healthy body fat percentage, and what happens when you're too lean.
06 / Limitations
Limitations and safety
A tape estimate is not a lab measurement. In a 2022 study of 430 male US Marines, the Navy tape equation read on average about 2.5 percentage points lower than a DXA scan, and individual results varied by several points either way. Compare your readings with each other, not with a scan or a smart scale that uses a different method.
The equations were developed in military personnel. They can be less accurate for people with unusual body shapes, for example a very thick, muscular neck (which pulls the estimate down) or, for men, fat carried mainly on the hips and thighs, which the men's equation does not measure.
Small measuring errors add up. In the worked example, a waist reading 1 cm too large adds about 0.7 of a point. Measure carefully, and the same way each time.
This calculator gives an estimate for general fitness education. It is not medical advice and does not diagnose anything. If you have a health condition, are pregnant, or are new to hard exercise, check with a doctor first.
07 / FAQ
Frequently asked questions
How accurate is the US Navy body fat calculator?
It is a reasonable estimate, not a precise measurement. Compared with DXA scans, the tape method is often a few percentage points out for an individual; one 2022 study of male Marines found it read about 2.5 points low on average. It is most useful for tracking your own change over time with consistent measuring.
How do I measure my waist for the Navy body fat method?
Men measure around the abdomen level with the navel. Women measure the natural waist at its narrowest point, usually about halfway between the navel and the breastbone, plus the hips at the widest part of the buttocks. Stand relaxed, do not pull your stomach in, and keep the tape level and snug.
What body fat percentage is considered lean?
In the American Council on Exercise categories, 14–17% for men and 21–24% for women is the "fitness" range, and 6–13% for men and 14–20% for women is typical of athletes. Below that you move towards the essential-fat range (2–5% for men, 10–13% for women).
What is an average body fat percentage?
ACE lists 18–24% as average for men and 25–31% for women. It classes 25% or more for men and 32% or more for women as obese.
Can I use inches instead of centimetres?
Yes. Switch the units to inches and enter your height in feet and inches. The calculator converts everything to centimetres and uses the metric Navy equations, which give almost the same answer as the inch version the US military publishes.
Why is my waist required to be bigger than my neck?
The equations use the logarithm of waist minus neck (or waist plus hips minus neck for women), which only works when that number is positive. If your waist reads smaller than your neck, one of the measurements is almost certainly wrong or in the wrong unit.
Is this the same as the Army body fat calculator?
No. This page uses the classic US Navy neck-and-waist method. Since July 2026 the US Army has used a waist-to-height ratio instead of a tape body fat test; use the Army body fat calculator for that standard.
How often should I measure my body fat?
Every two to four weeks is plenty. Body fat changes slowly, and measuring more often mostly picks up day-to-day noise from food, water and measuring technique.
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.
- US Army. Army Regulation 600-9, The Army Body Composition Program. 28 June 2013. Appendix B.
- Potter AW, Tharion WJ, Holden LD, Pazmino A, Looney DP, Friedl KE. Circumference-based predictions of body fat revisited: preliminary results from a US Marine Corps body composition survey. Front Physiol. 2022;13:868627.
- American Council on Exercise (ACE). Percent body fat categories.
- US Army. Army Body Composition Program frequently asked questions (Army Directive 2026-06). 2026.
Related tools
- Army Body Fat CalculatorCheck the Army’s current body composition standard: waist-to-height ratio under 0.55, which replaced the tape test in July 2026.
- BMI CalculatorWork out your body mass index in kg/cm or lb/ft, see your category and the healthy-weight range for your height.
- TDEE CalculatorEstimate the calories you burn per day, then get a target for losing, keeping or gaining weight.
From the blog
Exercises to try
- Barbell SquatsBeginner compound barbell exercise for the quadriceps, also working the glutes.
- Barbell DeadliftIntermediate compound barbell exercise for the hamstrings, also working the glutes, abs and calves.
- Bent Over RowsBeginner compound barbell exercise for the middle back, also working the lats, shoulders and lower back.
- PushupsBeginner compound bodyweight exercise for the chest, also working the triceps and shoulders.
- PlankBeginner compound bodyweight exercise for the abs, also working the quadriceps.
Change the number with a plan
GymStreak builds workouts around your goal, logs every set in kg or lb, and lets you log meals from a photo or a quick description, so fat loss has a daily plan behind it.
