Body Fat Calculator
Body fat calculator: your body fat percent by the US Navy tape method, with BMI cross-check, fat mass and lean mass. Free, no sign-up, and it runs in your browser.
Dedicated page: /en/body-fat-calculator
Estimate only, not medical advice. Tape methods are screening estimates, typically within 3 to 5 percentage points of a DEXA scan. They cannot diagnose health conditions.
Just below the Adam's apple, tape sloping slightly down at the front.
Men: at the navel. Women: narrowest point, usually just above the navel.
Use the target to see how much fat you would need to lose at your current lean mass.
How to measure: use a flexible, non-stretch tape, snug but not compressing the skin. Take each measurement twice and average the two. Measure in the morning, before eating, for the most consistent numbers.
Quick answer
A body fat calculator estimates your body fat percentage from simple tape measurements. The US Navy method uses your neck, waist, hip and height, and a BMI method cross-check uses your height, weight and age. It also gives your fat mass, lean mass, category and the fat to lose to reach a goal.
About this Body Fat Calculator
Body fat calculator: your body fat percent by the US Navy tape method, with BMI cross-check, fat mass and lean mass. It is one of the Health and Family on ToolUstad, and like every tool here it runs entirely in your browser: nothing you type, paste or open is uploaded to a server, and there is no sign-up or usage limit.
What is a body fat calculator?
A body fat calculator estimates the share of your weight that is fat, as opposed to lean mass: muscle, bone, organs and water. This tool adds a second estimate from the BMI method, so you can compare the two.
How the US Navy method works
For men, the formula is 495 divided by 1.0324 minus 0.19077 times the log of waist minus neck, plus 0.15456 times the log of height, minus 450, with all measurements in centimetres. For women, the waist term becomes waist plus hip minus neck, with different constants, and the same centimetre rule applies. The tool converts inches automatically, because the inch version of the formula uses different constants and mixing them up gives a wrong answer. The method is usually within 3 to 4 percentage points of a DEXA scan when measurements are taken carefully.
The BMI method cross-check
The BMI method, also called the Deurenberg formula, estimates body fat from BMI, age and sex: 1.20 times BMI plus 0.23 times age, minus 16.2 for men or 5.4 for women. It is quick, but it cannot tell muscle from fat, and its error is about 4 to 5 points. Its value is as a cross-check: when the two figures agree, your estimate is more reliable.
Categories and the age-based ideal
The American Council on Exercise publishes the standard categories: essential fat is 2 to 5% for men and 10 to 13% for women, athletes are 6 to 13% for men and 14 to 20% for women, fitness is 14 to 17% for men and 21 to 24% for women, and average is 18 to 24% for men and 25 to 31% for women. Healthy ranges rise gently with age, so this tool also reports the Jackson and Pollock ideal for your age.
Fat mass, lean mass and the goal
A percent alone is hard to act on, so the tool splits your weight into fat mass and lean mass. Tracking lean mass matters when you diet: the goal is to lose fat while keeping lean tissue.
Best practices
- Measure in the morning, before eating, with a flexible non-stretch tape, snug but not compressing the skin.
- Measure at the same spots every time: men at the navel, women at the narrowest point, neck just below the Adam's apple.
- Track the trend over months, not one reading: single readings carry several points of error.
Common mistakes
- Pulling the tape tight, which understates the waist and flatters the result.
- Measuring after a meal or after training, when the waist is temporarily larger.
- Chasing a very low percent: essential fat is real, and going below it harms health.
Who this tool is for
It is for anyone tracking body composition while training or losing weight, who wants more than a scale number. It needs no equipment beyond a tape measure and no account. For a clinical measurement, a DEXA scan or air-displacement test is the standard, and a doctor is the right person to interpret the result.
Learn: how to use the Body Fat Calculator
- Pick imperial or metric, your sex, and your age.
- Enter your height and weight.
- Measure your neck and waist with a tape, and your hip if you are a woman.
- Read the Navy result, the BMI cross-check, your fat and lean mass, and the goal.
Features
- US Navy method from neck, waist, hip and height
- BMI method cross-check from height, weight and age
- Fat mass and lean mass in kilograms and pounds
- Body fat category by sex, from the American Council on Exercise
- Jackson and Pollock ideal body fat for your age
- Goal mode: fat to lose to reach any target percent
- Metric and imperial units, with conversion when you switch
- Measurement guide for neck, waist and hip
Worked example
A 35-year-old man, 180 cm tall, 80 kg, with a 90 cm waist and a 38 cm neck: the US Navy method gives 19.8% body fat, which is 15.8 kg of fat and 64.2 kg of lean mass. The BMI method gives 21.5% as a cross-check, and his BMI is 24.7. The Jackson and Pollock ideal for his age is about 13.8%. To reach 15% body fat while keeping his lean mass, he would weigh about 75.5 kg and need to lose about 4.5 kg of fat.
Frequently asked questions
How does the US Navy method work?
It estimates body fat from tape measurements: height, neck and waist for men, plus hip for women. The measurements feed a logarithmic formula developed for the US Navy in 1984. It is a screening estimate, usually within 3 to 4 points of a DEXA scan when measured carefully.
Why do I need a hip measurement as a woman?
The female Navy formula includes the hip because women store a greater share of fat in the hip and gluteal region. Including it improves accuracy. The male formula omits the hip because it adds little predictive value for men.
What is a healthy body fat percent?
For men, the American Council on Exercise puts fitness at 14 to 17% and average at 18 to 24%. For women, fitness is 21 to 24% and average is 25 to 31%. Healthy ranges rise gently with age.
Why do the Navy and BMI methods disagree?
The Navy method uses where you carry girth, so it reflects body shape. The BMI method uses only height, weight and age, so it cannot tell muscle from fat: a muscular person reads as fatter than they are. When the two agree, trust the number more.
How accurate is a tape measurement?
Within about 3 to 5 percentage points of a DEXA scan for most adults, which is the gold standard. Accuracy falls for very muscular people, older adults with muscle loss, and anyone who measures loosely. Take each measurement twice and average them.
How do I measure my waist correctly?
Use a flexible, non-stretch tape, snug but not compressing the skin. Men measure at the navel, women at the narrowest point, usually just above the navel. Measure in the morning before eating, and do not pull the tape tight.
How fast can body fat change?
Slowly: about 0.5 to 1 percentage point a month of sustained change. Losing fat while keeping lean mass needs a modest calorie deficit, enough protein, and strength training. Crash diets lose lean mass as well as fat.
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