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Body Fat Calculator

Estimate body fat from tape measurements or BMI, with fat and lean mass and a cited category table.

By Nitin Raturi · Last reviewed

Your measurements

How to use this Body Fat Calculator

Enter a few body measurements to get two rough estimates of body fat. Nothing you type leaves your browser.

  1. Choose your units and sex.
  2. Measure your neck, waist and, if you chose Female, your hips with a soft tape. Add your height, weight and age.
  3. Read the two estimates and compare them with the category table.
  4. Check the fat mass and lean mass split and the notes on how accurate each method is.
  5. Measure again in the same way on another day to see whether a change is bigger than normal measuring noise.

Good to know

  • The two methods can differ by several percentage points. That is normal.
  • These are estimates, not a diagnosis. A health professional can advise on your situation.
  • Tap the ⓘ next to a field for how to measure it.

Enter your details to see two rough estimates. The calculation stays in your browser.

Units

Units

Whether you type lengths in centimetres and weight in kilograms, or lengths in inches and weight in pounds.

How to fill it in

  • Pick the units you measured in.
  • Switching converts the numbers already in the form, so the estimate stays essentially the same.

Example

180 cm is the same as 70.9 inches.

Sex

Sex

Both formulas were fitted separately for men and women, so each uses one of two sets of coefficients.

How to fill it in

  • Choose Male or Female.
  • Choosing Female also uses your hip measurement for the Navy method.

Keep in mind: The formulas have two versions only. They do not describe everyone, so treat the result as a rough guide.

Age

Your age in whole years. Only the BMI-based method uses it.

How to fill it in

  • Allowed range: 18 to 99 years.
  • The BMI-based estimate rises by 0.23 percentage points for each extra year.

Example

At age 30 the BMI-based estimate is 20.3%.

Height

Your standing height without shoes.

How to fill it in

  • Allowed range: 100 to 250 cm.
  • Stand against a wall with your heels together and measure to the top of your head.

Example

With 80.0 kg at 180 cm, your BMI is 24.7.

Weight

Your body weight. It sets the BMI and is split into fat mass and lean mass.

How to fill it in

  • Allowed range: 30 to 300 kg.
  • Weigh yourself at a similar time of day each time, so comparisons are fair.

Example

At 80.0 kg, the Navy estimate of 16.1% means about 12.9 kg of fat mass.

Neck

The distance around your neck, just below the larynx.

How to fill it in

  • Allowed range: 20 to 70 cm.
  • Keep the tape level and snug without squeezing, with your head facing forward.

Tip: A larger neck with the same waist lowers the Navy estimate.

Waist

The distance around your waist.

How to fill it in

  • Allowed range: 40 to 250 cm.
  • Men: measure at the navel. Women: measure at the narrowest point of the waist.
  • Breathe out normally and keep the tape level.

Example

A 85 cm waist with a 38 cm neck gives a Navy estimate of 16.1%.

Keep in mind: Where you place the tape changes the estimate. Measure the same way each time.

Hip

The distance around the widest part of your hips and buttocks. Only the Navy formula for women uses it.

How to fill it in

  • Allowed range: 50 to 250 cm.
  • Stand with your feet together and keep the tape level all the way around.
  • If you chose Male, this field is ignored.

Not used for men.

Measure with a soft tape on bare skin, and measure twice. Small differences in tape placement change the result.

Your body fat estimates

Two formulas, two answers. They use different inputs, so they rarely agree exactly.

US Navy method

Uses neck, waist, height (and hip for women)

16.1%

ACE category: Fitness

Estimated fat mass
12.9 kg
Estimated lean mass
67.1 kg

Individual results can be off by several percentage points.

BMI-based method

Uses BMI 24.7, age and sex

20.3%

ACE category: Average

Estimated fat mass
16.3 kg
Estimated lean mass
63.7 kg

Typical error in the original study: about 4 percentage points (4.1).

These are estimates, not a measurement or a diagnosis. The gap between the two methods here is 4.2 percentage points. For health decisions, talk to a qualified healthcare professional.

Body fat categories for men

American Council on Exercise (ACE) ranges, shown for the sex you selected.

ACE body fat percentage categories for men
CategoryRangeYour estimate
Below the essential rangeunder 2%
Essential fat2–5%
Athletes6–13%
Fitness14–17%US Navy
Average18–24%BMI-based
Obese (ACE label)25% and above

Source: ACE category ranges, accessed 22 October 2026. A category is a general reference, not a health verdict. The published ranges leave small gaps between whole numbers; a value in a gap is placed in the lower category.

ChangelogHow we test this calculatorEmbed this calculator

How this calculator works

Two formulas give two rough answers. For the default example they are 16.1% from tape measurements and 20.3% from height and weight.

  1. Step 1Measure85 cm waistwith a 38 cm neck and 180 cm height
  2. Step 2Apply two formulas16.1%US Navy; the BMI-based formula gives 20.3%
  3. Step 3Split your weight12.9 kgof fat and 67.1 kg of lean mass at 80.0 kg

The US Navy method, published by Hodgdon and Beckett in 1984, compares your waist with your neck and height. The BMI-based method, from Deurenberg and colleagues in 1991, uses BMI, age and sex.

What the result leaves out

  • Not a direct measurementNeither formula looks inside the body. Imaging and lab methods measure body composition more directly.
  • Muscle and buildThe BMI-based formula cannot tell muscle from fat, so it can mislead very muscular or very lean people.
  • Tape placementA small change in where the tape sits changes the Navy result.
  • Age and populationBoth formulas were fitted on particular groups of adults and may fit you less well.

Worked example

A 30-year-old man, 180 cm, 80 kg, neck 38 cm, waist 85 cm
US Navy (men, cm)
BF% = 495 ÷ (1.0324 − 0.19077·log10(waist − neck) + 0.15456·log10(height)) − 450
BMI-based (adults)
BF% = 1.20·BMI + 0.23·age − 10.8·sex − 5.4, with sex = 1 for men and 0 for women
  1. Waist minus neck85 − 3847 cm
  2. Log of waist minus necklog10(47)1.6721
  3. Log of heightlog10(180)2.2553
  4. Denominator1.0324 − 0.19077 × 1.6721 + 0.15456 × 2.25531.0620
  5. US Navy estimate495 ÷ denominator − 45016.1%
  6. BMI80 ÷ 1.80²24.7
  7. BMI-based estimate1.20 × BMI + 0.23 × 30 − 10.8 − 5.420.3%
  8. Fat mass (Navy)16.1% of 80.0 kg12.9 kg
  9. Lean mass (Navy)weight − fat mass67.1 kg

Figures are rounded for display; the calculation keeps full precision. It works in centimetres and kilograms, converting inches and pounds first.

Reading your result

  • US Navy16.1%ACE category: Fitness. It uses tape measurements, so it reacts to changes in your waist.
  • BMI-based20.3%ACE category: Average. It uses only height, weight, age and sex, so it cannot see where weight sits.
The two can disagree by several percentage points. Treat them as a rough range, not one exact figure.
  • US Navy estimate
  • BMI-based estimate
  • US Navy16.1%
  • BMI-based20.3%
Same person, two formulas. The gap is a reminder that both are estimates.

How accurate are these estimates?

The BMI-based study reported a standard error of about 4.1 percentage points and noted that it tended to overestimate fat in obese people. Navy results can also be off by several points for an individual. Measuring the same way each time makes your own readings easier to compare.

The category table uses ranges from the American Council on Exercise (ACE). A category is a general reference, not a verdict on your health.

Other measures of body size

Body fat is one view of body composition. BMI, energy needs and protein intake answer different questions.

The BMI calculator compares weight with height using WHO categories, and the ideal weight calculator compares several published formulas. To plan meals around a goal, the BMR and TDEE calculator estimates daily energy, and the macro calculator splits it into protein, carbs and fat.

Common mistakes

  • Mistake: Treating the result as exact.

    Instead: Read it as a rough range and compare only readings taken the same way.

  • Mistake: Placing the tape at a different spot each time.

    Instead: Use the same landmarks and a level tape, measured after a normal breath out.

  • Mistake: Trusting the BMI-based figure for a very muscular body.

    Instead: Lean on the tape-based estimate, or ask a professional about direct methods.

  • Mistake: Using the result to diagnose a condition.

    Instead: Talk to a qualified healthcare professional about your situation.

This tool is for general information and is not medical advice, diagnosis or treatment. Talk to a qualified healthcare professional about your situation.

Checking the method

A separate script evaluates every test case in two precisions and checks each against the recorded test values to six decimals.

Read how we test our calculators, or browse more health calculators.

Frequently asked questions

How is body fat estimated here?

Two published formulas are used. The US Navy method uses neck, waist, height and, for women, hip circumference. The BMI-based method uses BMI, age and sex.

How accurate are the results?

They are estimates. The BMI-based study reported a standard error of about 4.1 percentage points, and the Navy method can also be off by several points for an individual.

Why do the two results differ?

They use different inputs. The Navy method sees your waist, while the BMI-based formula only sees height, weight, age and sex, so it cannot separate muscle from fat.

Where do I measure my neck, waist and hip?

The Navy method measures the neck just below the larynx, the waist at the navel for men and the narrowest point for women, and the hip at its widest point. Keep the tape level and snug.

Can I enter inches and pounds?

Yes. Switch the unit and enter inches and pounds. The calculation converts them to centimetres and kilograms first, so both units give the same answer.

Why does it ask for a hip measurement only for women?

The published Navy equation for women includes the hip. The men’s equation does not use it, so the field is ignored for men.

What do the category ranges mean?

They are general reference ranges published by the American Council on Exercise. A category does not diagnose anything about your health.

Is this medical advice?

No. It is general information, not a diagnosis. Talk to a qualified healthcare professional about your situation.

Sources and methodology

The formulas are standard time-value-of-money results. We check every figure against golden values worked out independently, by closed form and by month-by-month simulation; see the methodology.

Written and maintained by Nitin Raturi, a software engineer (about the author). Last reviewed 22 Oct 2026; next review due by . Found an error? Tell us.

Changelog

  • : Registered at the owner's request; ACE range table still to be re-checked against the live source. Estimates body fat with the US Navy and BMI-based formulas. The default example gives 16.1% and 20.3%.

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