How to Calculate Body Fat Percentage at Home

Body fat calculation title card with measuring tape

The quickest way to calculate body fat percentage at home is the U.S. Navy circumference method. You need a soft tape measure, your height and a few body measurements, and the result is an estimate, usually within a few points of lab methods. Our body fat calculator does the math in your browser. Below you will find the formulas it uses, two worked examples, the BMI shortcut, and how to read the number you get.

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TL;DR

The Navy method uses height, neck and waist (plus hips for women) and a logarithmic formula. It is the most practical home option.
A BMI-based formula also exists, but BMI cannot tell muscle from fat, so treat that result as a rough guide only.
Skinfold calipers can work well, but the result depends on the skill of the person measuring.
Measure the same way, at the same time of day, and watch the trend rather than a single reading.
Our free calculator runs the Navy formula for you, with no download or sign-up.

What body fat percentage actually measures
The U.S. Navy formula, step by step
The BMI shortcut and how to work out BMI correctly
Skinfold calipers: more detail, more skill needed
Which method should you pick?
What your number means
Get a reading you can trust
Our perspective
Try the calculator
FAQ
Sources

What body fat percentage actually measures

Body fat percentage is the share of your total weight that is fat. A 180 lb person at 20% carries 36 lb of fat and 144 lb of everything else: muscle, bone, organs and water. That is why it tells you more than the scale does. Two people with the same weight and height can have very different percentages.

A home calculation is always an estimate. Lab methods such as DXA scans, hydrostatic weighing and the Bod Pod measure body composition more directly, but they cost money and need an appointment. Formulas predict your fat from measurements that are easy to take, and they are accurate enough for tracking your own progress over weeks and months.

The U.S. Navy formula, step by step

The Navy method estimates body fat from circumferences. According to a university anthropometrics lab guide, men need height, neck and waist (abdomen) circumference, and women additionally need hip circumference. The guide gives separate logarithmic equations for each sex.

Navy formula measurement sites by sex

The formulas

All measurements are in inches, and log10 is the base-10 logarithm, which is a button on most scientific calculators.

Men: body fat % = 86.010 × log10(abdomen − neck) − 70.041 × log10(height) + 36.76. This version of the equation is printed in a 2022 review of circumference-based predictions.

Women: body fat % = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387.

If typing logarithms into a phone calculator sounds tedious, that is the reason online calculators exist. Our tool takes your measurements in imperial or metric and returns the result in one step.

How to take the measurements

Tape technique matters more than most people expect. The Measurement Toolkit lists tape tension, trouble finding the right anatomical site and differences between measurers as the main sources of error. A few habits reduce them:

Use a mirror to check that the tape is level all the way around, a tip also given in the toolkit.
Keep the tape snug, not tight. It should rest on the skin without denting it.
Neck: measure just below the Adam’s apple, with the tape sloping slightly down toward the front.
Waist or abdomen: for most men, level with the navel. Women’s waist is usually the narrowest point of the torso, though the university guide notes it varies.
Hips (women): the widest part of the buttocks, feet together.
Height: barefoot, back against a wall, looking straight ahead.
Breathe out normally before reading, and do not pull in your stomach.
Measure twice and use the average. The toolkit suggests recording to the nearest 0.1 cm, which is about 0.04 inch, so note the reading as precisely as your tape allows.

Worked example for a man

Say a man is 70 inches tall, with a 36 inch abdomen and a 15 inch neck.

Abdomen minus neck: 36 − 15 = 21
log10(21) ≈ 1.322, and 86.010 × 1.322 ≈ 113.73
log10(70) ≈ 1.845, and 70.041 × 1.845 ≈ 129.23
113.73 − 129.23 + 36.76 ≈ 21.3

His estimated body fat is about 21%.

Worked example for a woman

Now a woman who is 65 inches tall, with a 31 inch waist, 40 inch hips and a 13 inch neck.

Waist plus hip minus neck: 31 + 40 − 13 = 58
log10(58) ≈ 1.763, and 163.205 × 1.763 ≈ 287.80
log10(65) ≈ 1.813, and 97.684 × 1.813 ≈ 177.09
287.80 − 177.09 − 78.387 ≈ 32.3

Her estimated body fat is about 32%.

Notice how sensitive the result is. Being off by an inch at the waist shifts the answer by roughly a point or more. That is why repeating the measurement and keeping your technique identical matters.

Woman checking waist circumference with tape

The BMI shortcut and how to work out BMI correctly

BMI is the starting point for many quick estimates. Health Canada defines it as weight in kilograms divided by height in meters squared (kg/m²). If you use pounds and inches, a calculator handles the conversion for you, and our BMI calculator accepts both unit systems.

A BMI-based body fat formula adds age and sex. A 2022 review of BMI as a measure of body fatness reports it for adults as:

body fat % = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4

Here sex is 0 for women and 1 for men. For a 35-year-old man with a BMI of 25, that gives 30 + 8.05 − 10.8 − 5.4, or about 21.9%.

This is the weakest of the home methods. BMI does not separate muscle from fat, and Wikipedia’s overview of body fat percentage notes that such formulas slightly overestimate fat in obese people. A muscular person and a person with little muscle can share a BMI and have very different body fat. Use the BMI formula as a sanity check next to a circumference estimate, not as your main number.

Skinfold calipers: more detail, more skill needed

Skinfold methods pinch the skin and underlying fat at set body sites. The Harvard Nutrition Source explains that the formulas need thickness readings from at least three body parts, such as the torso, thighs, upper arm and below the shoulder blade. A university exercise-testing manual describes the three-site version: chest, abdomen and thigh for men, or triceps, suprailiac crest and thigh for women, along with age, height and weight.

Calipers are cheap. The British Heart Foundation says a basic set can cost £4 to £10. The catch, per Harvard, is that results depend on the measurer’s skill and training. Two people using the same formula can get different numbers. If you go this route, measure the same sites on the same side of the body, take each fold two or three times, and ideally have the same person do it every time.

Which method should you pick?

Method	What you need	Effort	Main weakness
Navy circumference	Soft tape, height	Low	Sensitive to tape placement
BMI-based formula	Weight, height, age, sex	Lowest	Cannot tell muscle from fat
Skinfold calipers	Calipers, trained hands	Medium	Depends on technique
Lab scan (DXA and similar)	Appointment	High	Cost and access

For most people at home, the Navy method is the best balance. It needs one cheap tool and produces a repeatable number. Research on more elaborate equations shows what is possible: a 2021 study combining skinfolds with waist circumference, tested against a five-compartment criterion model, reached a standard error of estimate of 2.5%. A 2022 study of field methods adds that these approaches are valid for informing on body adiposity but that the equation should suit your age and ethnic background. In plain terms: expect an estimate within a few points, not a precise figure.

What your number means

Once you have a percentage, compare it with a reference chart. The American Council on Exercise ranges, reproduced in a published copy of its chart, look like this:

Category	Men	Women
Essential fat	2-5%	10-13%
Athletes	6-13%	14-20%
Fitness	14-17%	21-24%
Average	18-24%	25-31%

Our two worked examples, about 21% for the man and about 32% for the woman, land in the average band and just above it. A single reading is a snapshot. The useful questions are whether the number is moving in the direction you want, and whether your waist is shrinking while your strength holds.

One companion check is simple. The British Heart Foundation says a waist-to-height ratio from 0.5 to 0.59 suggests an increased risk of health problems, and 0.6 or above suggests an even higher risk. To calculate it, divide your waist by your height in the same units. A 36 inch waist at 70 inches tall gives 0.51. If your ratio is in those higher bands, or you have concerns about your weight, talk with your doctor rather than relying on a calculator.

Get a reading you can trust

The aim is not a perfect number. It is a number you can compare with next month’s. These habits keep your tracking honest:

Same time, same conditions. Measure in the morning, before eating, in the same state of hydration.
Same tape, same spots. Mark the sites mentally against landmarks such as the navel, and use a mirror.
Monthly, not daily. Body fat changes slowly, and daily measurements mostly record noise.
Pair it with other data. Log your weight, waist and how clothes fit. If you are also adjusting food intake, our calorie calculator estimates your daily needs.
Use one calculator. Different tools use slightly different formulas, so switching between them mixes up the trend.

If you want to turn the percentage into pounds, multiply your weight by the percentage. At 180 lb and 20%, that is 36 lb of fat. The percentage calculator handles this in a second.

Our perspective

We built the body fat calculator because most people who search for this want an answer in under a minute, not an account to create or an app to install. The Navy formula suits that goal. It needs a tape measure and a few numbers, and it is well documented.

Our design choices follow from the same idea. The calculator runs in your browser and processes your numbers locally, so your measurements are not something you hand over to a service. It works on a phone while you stand with the tape in your hand, and it accepts imperial and metric units so you are not stopping to convert.

We also think a result is only useful if it is clear, so the tool is designed to show the number plainly and let you repeat the measurement as often as you like. Pair it with the BMI, calorie and percentage calculators on the same site and you have a small health toolkit in one place, free to use.

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Try the calculator

Our free body fat calculator uses the U.S. Navy method. Enter your height and circumferences, and you get your estimate right away. It needs no download, installation or sign-up, and you can browse the rest of the health and fitness calculators in the same place.

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FAQ

How do I calculate body fat percentage without special equipment?

Use a soft tape measure and the Navy formula. Men need height, neck and abdomen measurements, and women add hips. Enter them into a calculator or the logarithmic formula above to get your estimate.

What is the body fat percentage formula for BMI?

For adults, one published version is 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, with sex coded 0 for women and 1 for men. It is only a rough guide, because BMI cannot distinguish muscle from fat. Use it alongside a circumference estimate.

How do I work out BMI correctly?

Divide your weight in kilograms by your height in meters squared. Measure height without shoes and weigh yourself on the same scale each time. If you use pounds and inches, a BMI calculator converts the units for you.

How accurate are home body fat calculators?

They give estimates, not exact readings. Tape placement and skinfold technique both affect the result, and equations work best when they suit your age and background. Research on better equations reports errors around 2.5 percentage points under good conditions, so expect a range rather than one precise figure.

How often should I measure my body fat?

Once a month is plenty for most people. Body fat changes slowly, and measuring too often mostly captures small differences in tape position or hydration. Measure in the same way each time and compare trends.