This body fat calculator uses the US Navy tape method, so a tape measure and two minutes are all you need. Your scale weight mixes muscle, fat, water and bone into one number. Body fat percentage splits that number into the part worth keeping and the part worth losing.
Take three measurements, or four if you are a woman, and the calculator handles the rest. It also gives you your fat mass, your lean mass and where you sit against standard fitness ranges.
How to Measure Yourself Properly
Bad measurements produce bad results. The tape does most of the work here, so take a minute over it.
Neck. Wrap the tape just below your larynx and let it slope very slightly down toward the front. Relax your shoulders and do not flex.
Waist for men. Measure at navel level with the tape parallel to the floor. Breathe out normally first and do not suck in.
Waist for women. Measure at the narrowest point of your torso, usually just above the navel.
Hips for women. Measure the widest part of your buttocks with your feet together.
Three habits improve accuracy more than anything else. Measure first thing in the morning before you eat or drink. Pull the tape snug so it sits flat without pressing into the skin. Take each measurement twice and use the average.
What Your Body Fat Percentage Means
Body fat ranges differ by sex because women carry more essential fat. That difference is biology, not fitness.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2 to 5% | 10 to 13% |
| Athletic | 6 to 13% | 14 to 20% |
| Fitness | 14 to 17% | 21 to 24% |
| Average | 18 to 24% | 25 to 31% |
| Above average | 25% and up | 32% and up |
Essential fat protects your organs and supports hormone production. Men who drop below 5 percent and women who drop below 13 percent usually pay for it with poor sleep, low energy and disrupted hormones. Lower is not automatically better.
The fitness band suits most people who want to look and feel healthy without organising their life around the gym. The athletic band takes real work to hold on to year round.
Body Fat Percentage Beats BMI for Most People
BMI divides your weight by your height squared and stops there. It cannot tell muscle from fat, so a lean rugby player and a sedentary office worker of the same weight get the same score.
The gap runs both ways. Plenty of adults sit in the normal BMI range while carrying 30 percent body fat, a pattern researchers call normal weight obesity. Their scale looks fine and their metabolic risk does not. Body fat percentage catches that. Our daily calorie calculator gives you the BMI figure too, so you can compare the two side by side.
The Formula Behind This Body Fat Calculator
Hodgdon and Beckett built these equations at the Naval Health Research Center in 1984, and the US military still uses the method for body composition screening. The equations predict body density from circumference measurements, then convert density to a fat percentage with the Siri equation.
Men need neck, waist and height. Women need neck, waist, hips and height, because fat distribution differs enough that one equation cannot cover both. Later Navy research confirmed the circumference approach as the best predictor of body fat among the field methods tested against hydrostatic weighing.
Age never enters the equation, which is one of its quirks. Two people with identical measurements get identical results at 25 and at 55, even though body composition typically shifts with age.
How Accurate Is the Tape Method
Expect to land within about 3 percentage points of a DEXA scan. That is close enough to be useful and loose enough that chasing decimal places wastes your time.
Accuracy drops at the extremes. Very muscular people with thick necks often score lower than they should, since a big neck reduces the waist minus neck figure. Very lean people and people carrying most of their fat on the legs rather than the middle can also read oddly.
The method earns its keep as a tracking tool. Measure the same way, at the same time of day, once a month. A drop from 26 percent to 23 percent over a season tells you something real even if the absolute numbers carry an error.
How to Lower Body Fat Without Losing Muscle
Fat loss and weight loss are not the same job. Aggressive dieting strips muscle alongside fat, which drops your metabolic rate and makes the weight easier to regain. Four things protect against that.
Keep the deficit modest. A shortfall of 300 to 500 calories a day suits most people. Work out your maintenance figure first with our daily calorie calculator, then subtract from there. The National Institute of Diabetes and Digestive and Kidney Diseases makes the same case for slow and steady loss.
Raise your protein. Protein needs climb during a deficit, not fall. Our protein intake calculator gives you a daily range in grams and in real food.
Lift something heavy twice a week. Resistance training gives your body a reason to hold on to muscle while you eat less. Cardio alone does not send that signal.
Protect your sleep. Short sleep raises appetite hormones and shifts weight loss toward muscle rather than fat. Our sleep calculator helps you pick a bedtime that fits whole cycles.
Who Should Not Rely on This Calculator
Researchers built the equations on healthy adults, so some groups get misleading results.
Pregnant and breastfeeding women. Body composition changes fast and the tape cannot follow it.
Children and teenagers under 18. Growth patterns need age adjusted charts instead.
People with fluid retention. Heart failure, kidney disease and some medications cause swelling that inflates the waist measurement.
People with loose skin after major weight loss. The tape reads that skin as fat.
Anyone with a history of disordered eating. Body fat tracking makes things worse for many people in this group. Talk to your clinician before you start.
Frequently Asked Questions
What is a healthy body fat percentage?
Most healthy men fall between 14 and 24 percent and most healthy women between 21 and 31 percent. The fitness band, 14 to 17 percent for men and 21 to 24 percent for women, works well as a target for general health.
How accurate is the US Navy body fat calculator?
It usually lands within about 3 percentage points of a DEXA scan. Accuracy drops for very muscular people, very lean people and anyone with significant fluid retention.
Can I use this calculator without a scale?
Yes. Height, neck and waist give you the percentage on their own. Your weight matters only for converting that percentage into fat mass and lean mass.
How often should I measure my body fat?
Once a month is enough. Body fat moves slowly, and weekly measurements mostly capture normal fluid shifts rather than real change.
Why did my body fat go up when my weight went down?
Fast weight loss often takes muscle with it, which raises the fat share of a smaller body. A smaller deficit, more protein and two strength sessions a week usually fix it.
Is this body fat calculator free?
Yes. No sign up, no email and no limits. Everything runs in your browser and nothing leaves your device.
Final Thoughts on Your Body Fat Calculator Result
A body fat calculator gives you a better picture of your body than the scale does, and it costs you a tape measure and two minutes. Treat the first result as your baseline rather than a verdict.
Measure again in four weeks with the same tape, the same time of day and the same technique. The direction of travel tells you whether your food and training are working. Browse the rest of our free health calculators to fill in the numbers around it.
This calculator provides a general estimate for healthy adults and does not replace advice from your doctor or a registered dietitian. Read our full medical disclaimer and fact checking policy.