Body Fat Calculator

Take a 5'10" man (70 inches) with a 15-inch neck and a 34-inch waist. The body fat calculator plugs those tape measurements into the U.S. Navy equation: 86.010 × log₁₀(34 − 15) − 70.041 × log₁₀(70) + 36.76, which works out to about 17.5% body fat - right at the boundary between the "fitness" and "average" ranges. At 175 lb that's roughly 31 lb of fat mass and 144 lb of lean mass. The same waist on a shorter or taller person gives a different result, which is exactly why height is part of the formula.

The formula

The U.S. Navy circumference method uses sex-specific equations. All measurements are in inches:

Because the equation uses base-10 logarithms of the circumference difference, the waist must be larger than the neck (and for women, waist + hip must exceed the neck). The calculator converts metric inputs to inches automatically before applying the formula.

How to measure correctly

Measurement technique matters more than anything else for accuracy. Use a flexible cloth or vinyl tape, keep it level, and pull it snug without compressing the skin:

• Neck: just below the larynx, tape sloping slightly down toward the front.
• Waist (men): horizontally at the navel.
• Waist (women): at the narrowest point of the torso.
• Hips (women): at the widest point of the buttocks.
• Measure after a normal exhale, don't suck in, and take each measurement twice and average it.

Body fat vs BMI

BMI uses only height and weight, so it can't tell muscle from fat - a lean, muscular athlete and a sedentary person of the same weight get the same BMI. Body fat percentage measures composition directly, separating fat mass from lean mass (muscle, bone, organs and water). That makes it a better gauge of fitness progress, though BMI is still a fast screening tool. Compare both with our BMI Calculator.

What's a healthy number?

There's no single ideal figure. Essential fat is about 2-5% for men and 10-13% for women - the minimum the body needs. General fitness ranges run roughly 6-17% for men and 14-24% for women, and healthy ranges drift upward with age. Treat these as guidelines and watch your trend over time rather than chasing one number.

How to use this calculator

You only need a tape measure, a scale, and a few minutes. Work through the fields in order:

1. Pick your units: choose imperial (inches and pounds) or metric (centimeters and kilograms). The calculator converts metric to inches internally before applying the Navy formula.
2. Select your sex: men use neck and waist; women add a hip measurement. The equation is different for each, so this choice changes which fields appear.
3. Enter height: measure barefoot, standing straight against a wall. Height anchors the formula, so an inch off here shifts the result.
4. Measure your neck: just below the larynx, with the tape sloping slightly down toward the front.
5. Measure your waist (and hips for women): follow the landmarks in the section above, after a normal exhale.
6. Enter your weight: this isn't used for the percentage itself, but it lets the calculator convert your body fat percentage into estimated fat mass and lean mass in pounds or kilograms.

The result updates instantly. Read your body fat percentage and category at the top, then check the fat-mass and lean-mass breakdown below it.

A second worked example (women)

Take a 5'5" woman (65 inches) with a 13-inch neck, a 30-inch waist, and 40-inch hips. The women's equation is 163.205 × log₁₀(30 + 40 − 13) − 97.684 × log₁₀(65) − 78.387, which works out to about 31% body fat - just above the "average" range for women. At 140 lb that's roughly 44 lb of fat mass and 97 lb of lean mass. Notice that the women's formula adds the hip measurement and uses larger coefficients, because fat distribution differs by sex and the equations were fitted separately to male and female reference data.

Body fat categories at a glance

The American Council on Exercise popularized a widely cited set of descriptive ranges. They are general guidelines, not medical thresholds, and they shift with age:

• Essential fat: about 2-5% (men), 10-13% (women) - the minimum needed for normal physiological function.
• Athletes: roughly 6-13% (men), 14-20% (women).
• Fitness: roughly 14-17% (men), 21-24% (women).
• Average/acceptable: roughly 18-24% (men), 25-31% (women).
• Above the healthy range: roughly 25%+ (men), 32%+ (women), where excess body fat starts to carry higher health risk.

Your calculator result lands in one of these bands automatically. Use the band as context, but remember that a lean, very muscular person and an older adult can both sit in "average" for different reasons.

Why fat mass and lean mass matter

The percentage alone hides useful detail. Splitting your weight into fat mass and lean mass tells you whether a change on the scale is fat, muscle, or water. During a diet, the goal is usually to lose fat mass while preserving lean mass - if both drop sharply, you may be losing muscle and should reconsider your protein intake and training. During a bulk, rising lean mass with only modest fat gain is the sign of a well-managed surplus. Tracking these two numbers, rather than body weight alone, gives a far clearer picture of what your body composition is actually doing.

Who this calculator is for

This tool turns a few tape measurements into a usable body composition number, so it fits anyone who wants more insight than a bathroom scale gives. That includes:

• Dieters and weight-loss trackers who want to confirm that the pounds coming off are fat rather than muscle. Pair it with our Weight Loss Calculator to plan a realistic timeline.
• Lifters and recomposition athletes tracking whether a bulk or cut is going as planned, often alongside an FFMI Calculator to gauge muscularity.
• Runners and endurance athletes monitoring composition without obsessing over scale weight.
• Service members and recruits preparing for a fitness assessment - though the military uses its own protocol, covered by our Army Body Fat Calculator.
• Anyone curious about where they sit relative to general fitness ranges, with no gym membership or lab visit required.

What affects your body fat percentage

Body fat percentage is the share of your total weight that is fat tissue, and several factors push it up or down over time:

• Energy balance: a sustained calorie surplus stores fat; a deficit burns it. This is the single biggest lever, and the Calorie Calculator and TDEE Calculator help you find your numbers.
• Muscle mass: more lean tissue lowers the percentage at the same weight and raises your resting calorie burn, which you can estimate with the BMR Calculator.
• Sex: women carry more essential fat than men for reproductive and hormonal reasons, which is why the formula and healthy ranges differ.
• Age: muscle is gradually lost and fat gained from middle age onward unless training counteracts it.
• Genetics and hormones: they influence where fat is stored and how easily it is lost, though they do not override energy balance.
• Activity and diet quality: resistance training, adequate protein, sleep, and stress management all shift the fat-to-lean ratio over weeks and months.

Body fat distribution: where the fat sits matters

Two people with the same body fat percentage can carry very different health risk depending on where that fat is stored. Subcutaneous fat sits just under the skin and is relatively benign. Visceral fat wraps around the organs in the abdomen and is far more strongly linked to heart disease, type 2 diabetes, and metabolic syndrome. The Navy method cannot tell the two apart - it only estimates total body fat - so a normal percentage with a large waist still warrants attention. A complementary measure is the ratio of your waist to your hips, which targets central fat directly; our Waist-to-Hip Ratio Calculator flags the abdominal pattern that carries the most risk. Using both numbers together gives a fuller picture than either alone.

How body fat shifts with age and sex

Healthy body fat is not one number for everyone. Women naturally carry roughly 8-10 percentage points more essential and storage fat than men, which supports hormone production and reproduction; this is normal and healthy, not a sign of being less fit. With age, body fat tends to creep up at the same waist and neck measurements because muscle mass declines - a process called sarcopenia - while fat is preserved or gained. The Navy equations include no age term, so the calculator will not adjust for this on its own. The practical takeaway is to read the category bands as guidelines that drift upward by a few points per decade, and to weight your personal trend over time more heavily than a comparison against a 25-year-old's ideal. Resistance training and adequate protein are the most effective ways to slow the age-related shift, which is why our Protein Calculator and Macro Calculator pair naturally with body fat tracking.

Tips to lower your body fat percentage

Body fat percentage falls when you reduce fat mass, build or keep lean mass, or both. Evidence-backed levers:

• Sustain a modest calorie deficit: a deficit of roughly 300-500 calories a day supports steady fat loss without crashing your metabolism or muscle.
• Prioritize protein: adequate protein (commonly cited as around 0.7-1 g per pound of body weight for active people) helps preserve lean mass while you lose fat.
• Lift weights: resistance training maintains and builds muscle, which raises lean mass and improves the ratio even if your weight barely moves.
• Stay active daily: walking and general movement burn meaningful calories and are easier to sustain than extreme cardio.
• Sleep and manage stress: poor sleep and chronic stress raise appetite hormones and make fat loss harder.
• Be patient: a healthy rate of fat loss is roughly 0.5-1% of body weight per week; faster usually means losing muscle and water.

How it compares to other body-fat methods

The Navy tape method is one of several ways to estimate body composition, each trading accuracy for convenience:

• Navy circumference (this tool): free, fast, repeatable at home; typically within 3-4 points of lab methods when measured carefully.
• Skinfold calipers: pinch fat at several sites; accurate in trained hands but sensitive to technique.
• Bioelectrical impedance (BIA): the scales and handheld devices that send a small current; convenient but swayed by hydration, food, and time of day.
• DEXA scan: a clinical X-ray scan considered a gold standard; very accurate but costs money and requires a facility.
• Hydrostatic (underwater) weighing & Bod Pod: lab methods based on body density; highly accurate but rarely available to the public.

For everyday tracking, the convenience and repeatability of the tape method usually beat the marginally higher accuracy of methods you'll only use once.

Key terms explained

• Body fat percentage: the proportion of your total body weight that is fat tissue, expressed as a percent.
• Fat mass: the actual weight of fat in your body, in pounds or kilograms - your weight multiplied by the body fat percentage.
• Lean mass (fat-free mass): everything that is not fat - muscle, bone, organs, connective tissue, and water.
• Essential fat: the minimum body fat needed for normal physiological function, about 2-5% for men and 10-13% for women.
• Circumference method: any technique that estimates body fat from tape measurements of body parts rather than from density or imaging.
• Visceral vs subcutaneous fat: fat stored around the organs versus just under the skin; the former carries more health risk.

How this calculator compares to related tools

This page answers "what is my body fat percentage from tape measurements?" If your question is slightly different, a sister calculator fits better:

• For a quick height-and-weight screen, use the BMI Calculator; it is faster but cannot separate fat from muscle.
• To estimate the lean tissue behind your weight directly, use the Lean Body Mass Calculator.
• To gauge muscularity relative to height, use the FFMI Calculator.
• To check abdominal fat risk specifically, use the Waist-to-Hip Ratio Calculator.
• To replicate the military standard, use the Army Body Fat Calculator.
• To find a sensible goal weight, use the Ideal Weight Calculator.

Limitations and assumptions

This calculator is a screening estimate, not a clinical measurement. Keep these limits in mind:

• It assumes typical fat distribution. Very muscular, very lean, very tall, very short, pregnant, or heavily edematous bodies can read several points off.
• It does not distinguish visceral fat (around the organs) from subcutaneous fat, even though visceral fat carries more health risk.
• It applies no age adjustment, though body fat naturally rises with age at the same circumferences.
• The equations were derived primarily from adult military populations and may be less accurate outside that range.
• Results depend almost entirely on measuring technique - the same body measured loosely or in the wrong spot can produce noticeably different numbers.

Sources

• National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), NIH - Weight Management and body composition basics.
• Centers for Disease Control and Prevention (CDC) - Assessing Your Weight.
• National Heart, Lung, and Blood Institute (NHLBI), NIH - Assessing Your Health Risk.
• Hodgdon, J.A. & Beckett, M.B. (1984), Naval Health Research Center - the original derivation of the U.S. Navy circumference body fat equations.