How to measure body fat at home: tape, calipers and scales compared

What are the ways to measure body fat at home?

There are three practical routes. You can measure body circumferences with a tape and put them in a formula. You can pinch skin folds with a caliper and use an equation. Or you can step on a scale that passes a small current through your body and estimates fat from the resistance it meets, a method called bioelectrical impedance analysis (BIA).⁷

All three give estimates. The research below compares each with a reference method, so you can see how big the gap tends to be. For what the numbers mean once you have one, read the body fat percentage guide.

How does the tape-measure method work?

The U.S. Navy circumference method, written as the Department of Defense equation, predicts percent body fat from height and two or three circumferences. A paper that tested it in men gives the formula with every measurement in inches.¹ A second paper gives both the men’s and women’s versions.²

How to take the men’s measurements

In the validation study, a trained technician used a non-stretchable fiberglass tape. Abdominal circumference was taken on bare skin at the level of the umbilicus, and neck circumference directly below the larynx. Height was measured in inches.¹

Worked example for a man

Take a made-up man who is 70 inches tall, with a 34 inch abdomen at the navel and a 15 inch neck. The arithmetic runs in four lines.

1. Abdomen minus neck: 34 − 15 = 19.
2. First term: 86.010 × log10(19) = 86.010 × 1.2788 = 109.99.
3. Second term: 70.041 × log10(70) = 70.041 × 1.8451 = 129.23.
4. Result: 109.99 − 129.23 + 36.76 = 17.5 percent body fat.

Now see how much one measuring slip matters. The table changes only the abdomen reading and keeps height at 70 inches and neck at 15 inches.

That is the practical lesson. The formula is stable when the tape goes in the same place each time and unstable when it does not. Mark the spot, measure twice, and take the same reading on the same bare-skin spot.

The accuracy picture is mixed. Among Navy personnel already declared to have excess fat, the procedure produced a 6.8% to 18% false positive rate, and the authors urged caution for individual decisions.³ In men followed for 9 months, the equation underestimated changes in percent body fat compared with air-displacement plethysmography, so it did not track small changes well.¹

How accurate are skinfold calipers at home?

A skinfold caliper pinches a fold of skin and fat at set sites. In a study of 50 college students, a digital caliper and a self-administered caliper were compared with DXA, with arm-to-arm and leg-to-leg impedance devices and with a three-site skinfold equation.⁴

The two consumer calipers had the poorest group accuracy, with total error of 7.9 to 10.9 percentage points of body fat. The digital caliper’s 95% limits of agreement were ±6.4 points in men and ±4.9 in women. The self-administered caliper’s were ±8.6 and ±7.5.⁴ The authors would not recommend either caliper for people with a body composition like their sample, and they recommended the three-site skinfold equation instead.⁴

A newer study of 49 Paralympic athletes found strong links between DXA body fat and the sum of skinfolds, but skinfold equations showed a negative bias of 2.0 to 7.9 points and large individual error compared with DXA.⁹ Skinfolds track the sum of folds well. The conversion to percent body fat is where the error enters.

Without trained technique and a second person to take the pinch, a home caliper is not a better route than a tape. We do not give caliper site instructions here because we did not read a source that sets them out.

How accurate is a body fat scale?

A scale with electrodes estimates fat from resistance. In 200 healthy Chinese adults, two consumer impedance devices correlated with DXA for percent fat at r = 0.89 and 0.90. There were small but significant biases, and the authors called the devices relatively accurate for percent fat in that group.⁶

Impedance does better with change over time than with a single figure. In 19 adults with obesity followed through a 12-month weight loss, impedance and DXA agreed on the fat lost: 7.0 kg by both. The authors wrote that impedance is at its best for fat mass or its changes. Compared with MRI, it overestimated visceral fat.⁵

The ESPEN guideline says impedance works well in healthy people with stable water and electrolyte balance and a validated equation suited to age, sex and race. It cannot be recommended for routine assessment at extremes of BMI or abnormal hydration, and following change over time is possible at BMI 16 to 34 without abnormal hydration, with caution.⁷

Water is the weak spot. Five hours of passive dehydration lowered body weight by 0.76 kg (1.7 lb) and an impedance estimate of fat mass by 0.90 kg (2.0 lb) in 25 men.⁸ A study of the Navy formula against impedance adds that readings may fluctuate right after activity, food or water, while a tape does not change with the time of day.² For more, see smart scale accuracy and DXA scan versus smart scale.

A home protocol you can repeat

1. Choose one method. Switching between a tape, a caliper and a scale mixes three different errors into your trend.
2. Fix the conditions. Same time of day, same spot, bare skin. For a scale, measure before eating, drinking or exercise.
3. Measure twice. If two readings differ, measure again and use the middle one.
4. Log the raw numbers. Write the circumferences or the scale’s figure, not only the final percent.
5. Compare every few weeks. Home methods carry errors of several percentage points, so a short interval mostly shows noise.
6. Judge against the error. A change smaller than the method’s error is noise. Check the table above.

A change smaller than the error

Here is the arithmetic of why this matters. A made-up person weighs 200 lb at 25% body fat, so fat mass is 50 lb (200 × 0.25). Suppose they lose 5 lb, all of it fat. Fat mass is now 45 lb and weight is 195 lb, so body fat is 45 ÷ 195 = 23.1%. The real change is 1.9 points.

That is smaller than the ±4.9 to ±8.6 point limits of agreement for the consumer calipers.⁴ A single caliper reading could not reliably show it. The same is true of any home method, which is why a trend of the same measure taken every few weeks, under the same conditions, is the only fair test.

Limits and when to ask for more

Home methods suit tracking, not judging. They do not tell you where your fat sits, and none of them replaces the advice of a clinician. The ESPEN guideline notes that impedance needs an equation that suits your age, sex and race, and that it is not recommended for routine assessment at extremes of BMI or abnormal hydration.⁷

If a home number worries you, or you are making a major change to your diet or exercise because of it, talk with a health professional. A clinic can use methods such as DXA, which the DXA comparison explains. For a waist-based check that needs only a tape, see waist-to-hip ratio and visceral fat.

Frequently asked questions