Body Fat Percentage Calculator
By Sofia Andersen · Last updated 15 October 2026
The scale tells you one thing. It cannot tell you what that weight is made of. Body fat percentage tries to answer the second question: how much of you is fat, and how much is everything else, muscle, bone, water, and the rest. A tape measure and the US Navy method can estimate it in a few minutes at home. It will not match a lab scan, but it is good enough to track change over time, which is usually the part that matters.
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General information only, not medical advice. If body composition or health is on your mind, talk with a qualified health professional. Urgent symptoms need urgent care, not a calculator.
Before you measure
You need a soft tape measure and a mirror. Measure in the morning, before eating, standing relaxed. Do not pull the tape tight, and do not hold your breath in. Pick male or female, then inches or centimetres. The result rounds to one decimal place.
Where the tape goes matters more than anything else:
- Height: without shoes, standing straight.
- Neck: around the middle of the neck, just below the Adam’s apple, tape snug but not squeezing.
- Waist: at the narrowest point of the torso for men, or at the navel for women using the Navy method. Keep the tape level.
- Hip (women): around the widest part of the buttocks, tape level.
Take each measurement twice. If the two readings differ by more than half an inch, take a third and use the middle value. Sloppy tape work is the whole ballgame here. A half-inch slip moves the answer, so the same spots, the same tension, and the same time of day are what make the next reading worth comparing.
What the tape is really doing
The US Navy method uses the ratios between these measurements, plus height, to estimate body fat. All measurements go in inches; if you measured in centimetres, divide by 2.54 first. The formulas use base-10 logarithms, which is why a calculator helps.
Men: 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
Women: 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
Women use the hip measurement because the method was fitted separately for each sex. The rest of the idea is the same: the waist-to-neck relationship carries most of the signal, and height scales it.
Take a man with a 34-inch waist, a 15-inch neck, and a height of 70 inches. Waist minus neck: 34 − 15 = 19. The log of 19 is 1.2788. The log of 70 is 1.8451. Next: 86.010 × 1.2788 = 109.99, and 70.041 × 1.8451 = 129.23. So 109.99 − 129.23 + 36.76 = 17.5%, rounded to one decimal place.
For a woman, the same steps use waist plus hip minus neck. With a 28-inch waist, 38-inch hips, a 13-inch neck, and a height of 64 inches: 28 + 38 − 13 = 53. The log of 53 is 1.7243, and the log of 64 is 1.8062. So 163.205 × 1.7243 = 281.42, and 97.684 × 1.8062 = 176.44. Then 281.42 − 176.44 − 78.39 = 26.6%.
Reading your number honestly
Body fat ranges that get quoted a lot look roughly like this. They are commonly cited bands, not targets handed down by nature:
| Group | Men | Women |
|---|---|---|
| Essential fat | About 2–5% | About 10–13% |
| Athletes | About 6–13% | About 14–20% |
| Fit | About 14–17% | About 21–24% |
| Average | About 18–24% | About 25–31% |
| Above average | 25% and up | 32% and up |
Essential fat is the minimum the body needs for hormones, nerves, and organ protection, which is why the floor is higher for women. Beyond that, there is a wide band of normal, and the healthiest number for any one person depends on age, habits, and medical history.
Expect error. A tape method can sit a few percentage points away from a DEXA scan. What it does well is show a trend: same tape, same spots, same time of day, once every few weeks. If the trend is moving the way you want, the exact number matters less.
BMI and body fat answer different questions. BMI only knows height and weight, so it cannot tell muscle from fat. This calculator tries to fill that gap. If calories are the next question, the calorie calculator estimates maintenance and deficit levels.
If this wasn’t the one, the ideal weight calculator gives a healthy weight range by height, and the BMR calculator shows what your body uses at rest. There is also a longer read, What is a good BMI?, on BMI versus body fat and where BMI falls short. Or browse all health calculators and all calculators on CalcKits.
Frequently asked questions
How do I measure body fat at home?
A tape measure and the US Navy method is the simplest way. Measure neck, waist, and hip for women, plus height, then put the numbers into the formula above or into the calculator. Measure twice for a steadier reading.
How close is the Navy method to a lab scan?
It is an estimate, usually within a few percentage points of a lab scan. Tape placement and tension are the main sources of error, so consistent technique matters more than chasing a decimal.
Why do BMI and body fat disagree?
BMI uses only height and weight, so a muscular person can score high while carrying little fat. Body fat percentage tries to split weight into fat and everything else, which is why the two numbers often tell different stories.
This page is general information. It is not medical advice, a diagnosis, or treatment, and it cannot replace a qualified health professional who knows your history. If symptoms worry you, or anything feels urgent, get urgent care rather than waiting on a calculator result.