Body Fat Calculator
Estimate your body fat percentage with nothing but a tape measure. This tool uses the U.S. Navy circumference method and also breaks your weight into fat mass and lean mass.
Measure with a snug tape, enter the numbers and press Calculate.
How to measure correctly
Neck
Wrap the tape just below the larynx, sloping slightly down at the front. Keep your shoulders relaxed and do not flex.
Waist
Men measure at the navel; women at the narrowest point. Stand naturally, breathe out gently and keep the tape level.
Hip (women)
Women also measure the widest part of the hips and buttocks. Take each reading twice and use the average for accuracy.
Why the tape method?
Nothing to buy
The Navy method needs only a flexible tape measure. No calipers, scales or clinic visit, which makes it easy to repeat at home and track over time.
Surprisingly reliable
For most people it lands within a few points of a professional caliper reading, and its real strength is consistency when you measure the same way each time.
Fully private
Your measurements are processed in your browser and never uploaded. Nothing is stored, so you can log a monthly check without sharing a thing.
Understanding body fat percentage
Body fat percentage is the share of your total weight that is fat, with the rest being muscle, bone, organs and water. It tells you something BMI cannot: two people at the same weight can look and function very differently depending on how much of that weight is fat.
The U.S. Navy formula
Developed for the military in the 1980s, this method estimates body fat from the circumference of your neck, waist and, for women, hips, adjusted for height. It is popular because it is free, repeatable and needs no special equipment beyond a tape measure.
Typical ranges
The American Council on Exercise publishes widely used reference bands. Women naturally carry more essential fat than men, which is why the healthy ranges differ.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Above average | 25%+ | 32%+ |
Fat mass and lean mass
Once you know your percentage, multiplying by your weight gives your fat mass in kilograms; the remainder is your lean mass. Watching lean mass hold steady while fat mass falls is a much better sign of progress than the scale weight alone, which can hide muscle gain.
Accuracy and limits
No tape-based estimate matches a DEXA scan, and results are most useful as a trend rather than an exact figure. Measure at the same time of day, ideally in the morning, and keep the tape snug but not compressing the skin for the most consistent readings.
Frequently asked questions
How accurate is the Navy method?
For most people it falls within about three to four percentage points of a caliper reading. Its biggest value is consistency, so it works best for tracking change over time rather than a single exact number.
Do I need calipers or a scale?
No. You only need a flexible tape measure. Weight is optional and is used purely to break your result into fat mass and lean mass.
Why do women enter a hip measurement?
The formula for women includes hip circumference because fat distribution differs between sexes. Men use only neck and waist.
Are my measurements uploaded?
No. Everything is calculated in your browser with JavaScript and nothing is sent to a server or saved after you leave.
What is a healthy body fat percentage?
Roughly 14 to 24% for men and 21 to 31% for women is considered fitness to average. Very low levels are only sustainable for athletes and can carry health risks.
When should I measure?
First thing in the morning, before eating or drinking, gives the most consistent baseline. Take each reading twice and average them.