Body Fat Calculator
Body fat % by tape (US Navy), skinfold or BMI method. Runs in your browser.
About this body fat calculator
This body fat calculator estimates what share of your weight is fat, using a tape measure (the US Navy method), skinfold calipers (Jackson-Pollock 3-site) or just your height and weight (the BMI method). It is for adults who want a better progress marker than the bathroom scale.
Along with the percentage you get your ACE category, fat mass and lean mass, the weight you would reach at a goal body fat if you kept your muscle, and your waist-to-height ratio. All of it works in centimetres and kilograms or in inches and pounds, and switching converts what you typed.
Each method has a known margin of error, so the page shows the formula it used with your numbers and a BMI-based figure for comparison.
Features
Three methods
US Navy tape (neck, waist, plus hips for women), Jackson-Pollock 3-site skinfolds with the Siri equation, or the Deurenberg BMI formula when you have no tape.
ACE category and scale
Your result on a colour bar with the American Council on Exercise bands: essential fat, athletes, fitness, average and obese, set for your sex.
Fat and lean mass
Body fat % times weight gives fat mass. The rest is lean mass: muscle, bone, organs and water.
Goal weight at a target %
Type a goal like 15% and see the weight you would reach if you lost only fat. The category table also shows the weight range for each band at your lean mass.
Waist-to-height ratio
With the tape method you also get waist divided by height. NICE suggests keeping it under 0.5.
Measuring hints
Each field says where to put the tape or caliper, since a 2 cm slip at the waist moves the Navy result by more than a point.
How to use the body fat calculator
- 1Choose units, sex and a method: tape measure, skinfold calipers or BMI.
- 2Enter age, height, weight and the measurements the method asks for.
- 3Read your body fat %, ACE category, fat and lean mass and goal weight.
When to use it
Tracking a cut
Measure every two weeks under the same conditions. Then plan the calorie deficit toward the goal weight the calculator gives you.
Checking a high BMI
If your BMI says overweight but you lift weights, the tape method shows whether that weight is fat or muscle.
Fitness tests
The US military checks body composition with tape measurements, so you can practise before the real check-in.
Second opinion on a smart scale
Bioimpedance scales swing with hydration. A tape or caliper reading taken the same morning tells you which number to trust.
How does the US Navy body fat formula work?
Hodgdon and Beckett built it at the Naval Health Research Center in 1984. It uses the fact that the waist grows with fat while the neck mostly tracks frame size. In centimetres, for men it is 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450.
Women add the hips: 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450.
Worked example: a man 178 cm tall with a 38 cm neck and an 88 cm waist. Waist minus neck is 50, and the formula gives 18.7%. At 80 kg that is about 15 kg of fat and 65 kg of lean mass. If you measured in inches, the calculator converts for you, or you can convert inches to centimetres yourself.
What is a healthy body fat percentage?
The ACE chart is the reference most gyms use. Women carry more essential fat than men, so the bands sit higher.
- Essential fat: women 10–13%, men 2–5%
- Athletes: women 14–20%, men 6–13%
- Fitness: women 21–24%, men 14–17%
- Average: women 25–31%, men 18–24%
- Obese: women 32% and up, men 25% and up
Tape, calipers or BMI: which is most accurate?
Skinfolds can be the closest at home, but only if you or a trainer take them the same way every time. The 3-site version uses chest, abdomen and thigh for men, and triceps, suprailiac and thigh for women.
The tape method is easier and repeatable. Its weak spot is people who carry fat mainly on the hips and thighs (men) or have a very thick neck from training.
The BMI method (Deurenberg, 1991) needs no measurements, but it cannot tell muscle from fat, so it reads high for lifters. Lab methods like DEXA are more precise than all three. For tracking, consistency beats precision: use one method and watch the trend.
Why use Mavros
| Mavros | Typical upload sites | |
|---|---|---|
| Methods | Navy tape, 3-site skinfold and BMI | Navy tape only |
| Goal weight | Weight at any target body fat, plus a range per category | Fat to lose to an age-based ideal |
| Extra checks | Waist-to-height ratio and a BMI-based comparison | None |
| Working shown | Formula with your numbers | Result only |
| Privacy | Measurements stay in your browser | Sent to a server with each click |
Tips
- Measure in the morning, before food or exercise, after using the toilet.
- Keep the tape level and snug, without pressing into the skin. Take each reading twice.
- Men measure the waist at the navel; women measure at the narrowest point.
- Compare your result with your BMI. If BMI is high but body fat is in the fitness band, the extra weight is mostly muscle.
- A 1% drop in body fat is easy to miss in the mirror. Trust the trend over 4 to 6 weeks.
Questions
How accurate is a body fat calculator?
Tape and skinfold methods are estimates and can be several percentage points away from a lab scan. Careful, repeated measuring makes them good for tracking change, even if the exact number is off.
What body fat percentage should I aim for?
For general health, the ACE fitness or average band is a sensible target: about 14–24% for men and 21–31% for women. Athletes often sit lower. Going below essential fat (about 2–5% for men, 10–13% for women) is unsafe.
How do I measure my neck and waist for the Navy method?
Measure the neck just below the Adam's apple with the tape sloping slightly down at the front. Men measure the waist level with the navel; women at the narrowest point. Breathe out normally and don't suck in.
Why is my result different from my smart scale?
Smart scales use bioimpedance, which depends heavily on how hydrated you are. The tape method depends on body shape. Both are estimates; pick one and use it the same way each time.
Can I use the calculator if I lift weights?
Yes. The tape and skinfold methods handle muscular people better than BMI. A very thick neck from training can push the Navy figure a little low.
What is lean body mass?
Everything that isn't fat: muscle, bone, organs and water. It is your weight minus your fat mass. Keeping it while you diet is the reason to lose weight slowly.
How much weight do I need to lose to reach a body fat goal?
Divide your lean mass by (1 − goal %). With 65 kg lean mass and a 15% goal, that is 65 ÷ 0.85 = 76.5 kg. Enter a goal and the calculator does it for you. To set that target against height-based formulas, see the ideal weight formulas.
Does this work for teenagers?
No. The formulas were built on adults, so the calculator asks for an age of 18 or over. For children and teens, doctors use BMI-for-age charts.
Is this medical advice?
No. It gives standard estimates. Talk to a doctor or dietitian before a big change in diet or training, especially if you have a health condition.