You can measure body fat at home with a tape measure, calipers, or a smart scale, or get a more precise reading from a clinical scan like DEXA or a Bod Pod. Each method trades off convenience for accuracy, and the best choice depends on whether you need a precise number or just want to track changes over time.
Why Body Fat Percentage Matters More Than Weight
Two people can weigh the same and carry very different amounts of fat. Body fat percentage tells you how much of your total weight is fat tissue versus muscle, bone, and organs. A 2025 study published in The Journal of Clinical Endocrinology & Metabolism proposed that body fat percentage can now replace BMI for defining overweight and obesity: 25% body fat or higher for men and 36% or higher for women qualifies as overweight, while 30% for men and 42% for women marks obesity. Below 18% body fat in men, and below 30% in women, researchers found essentially zero cases of metabolic syndrome, the cluster of conditions that raises your risk for heart disease and diabetes.
There is no universally agreed-upon “ideal” body fat percentage, as Harvard Health Publishing notes. But these thresholds give you a practical framework for interpreting whatever number you get.
The Tape Measure Method
The simplest way to estimate body fat at home is the U.S. Navy formula, which uses circumference measurements and your height. Men need two measurements: neck circumference (at the base of the neck, just below the Adam’s apple) and waist circumference (at the narrowest point above the hip bones, typically at the navel). Women need those two plus a hip measurement, taken at the widest point of the glutes with feet together.
You plug these numbers into a calculator (dozens of free ones exist online). The formula isn’t as precise as a scan, but it’s free, repeatable, and good enough to track trends. Use a flexible cloth tape, pull it snug without compressing the skin, and measure at the same time of day each time.
Smart Scales and Handheld Devices
Consumer body fat scales use bioelectrical impedance analysis, or BIA. The device sends a tiny electrical current through your body. Since fat tissue conducts electricity differently than muscle and water, the device estimates your body composition from the signal’s resistance.
The catch is that hydration swings the results significantly. In one study, drinking just 500 mL of water (about two cups) before a BIA reading caused body fat to be overestimated by roughly 2% in men and 3.4% in women. Drinking a liter bumped the error to nearly 4% and 6%, respectively. Exercise, meals, and even a full bladder shift the reading in the same way. Compared to clinical-grade methods, BIA readings can drift by several percentage points depending on your body’s water balance at the moment you step on the scale.
That doesn’t make smart scales useless. To get consistent readings, measure first thing in the morning, after using the bathroom, before eating or drinking anything. Wear minimal clothing (or none), stand barefoot on a hard flat surface, and distribute your weight evenly on both feet. Use the same scale every time. If you follow this routine, the absolute number may be off, but the trend line over weeks will still be meaningful.
Skinfold Calipers
Skinfold testing involves pinching a fold of skin and fat at specific body sites and measuring its thickness with calipers. The most common protocol, developed by Jackson and Pollock, uses three sites. For men: a diagonal fold on the chest (halfway between the front of the armpit and the nipple), a vertical fold two centimeters to the right of the navel, and the front of the mid-thigh. For women: the back of the upper arm at the midpoint of the tricep, a diagonal fold just above the hip bone, and the front of the mid-thigh.
The measurements feed into an equation that estimates total body fat. Calipers are inexpensive (a decent pair costs $10 to $30), but technique matters enormously. Having someone else take the measurements helps, and the same person should do it every time. A trained fitness professional will get more consistent results than a beginner. Even with good technique, skinfold tests are better for tracking change than for pinning down an exact percentage.
DEXA Scans
Dual-energy X-ray absorptiometry is widely considered the gold standard for noninvasive body composition testing. The scan uses two low-dose X-ray beams at different energy levels. Because fat, muscle, and bone each absorb these beams differently, the machine produces a detailed map of where each tissue type sits in your body. You get separate readings for each limb and your trunk, not just one total number.
A DEXA scan takes about 10 to 15 minutes. You lie still on a table while the scanner arm passes over you. The radiation exposure is minimal, roughly equivalent to a day or two of natural background radiation. Scans typically cost between $75 and $200 out of pocket, since insurance rarely covers body composition testing done for general fitness purposes. Many sports medicine clinics, university labs, and specialized body composition centers offer them.
Hydrostatic Weighing
Hydrostatic weighing, sometimes called underwater weighing, was the original lab-grade body fat test. You sit on a scale submerged in a tank of water after exhaling as much air from your lungs as possible. By comparing your weight on land to your weight underwater, the test calculates your body density, which converts to a fat percentage.
The method is accurate, but it has practical drawbacks. The biggest source of error is leftover air in the lungs: any air you don’t fully exhale makes you more buoyant and throws off the reading. Most protocols require multiple underwater trials to get a reliable result. People who are uncomfortable submerging themselves or who can’t fully exhale underwater tend to get inconsistent numbers. For these reasons, hydrostatic weighing has largely been replaced by newer options in most facilities.
Air Displacement (Bod Pod)
The Bod Pod works on the same density principle as underwater weighing but uses air instead of water. You sit inside a sealed egg-shaped chamber wearing minimal, tight-fitting clothing (loose fabric traps air and skews the reading). The machine measures the volume of air your body displaces, calculates your body density, and converts it to fat and lean mass percentages.
The experience is far more comfortable than being dunked underwater. You breathe normally while sitting still for two to three minutes. The device also measures your thoracic gas volume, the air inside your lungs during normal breathing, and corrects for it automatically. Hair should be compressed with a swim cap, since it traps air. Bod Pods are found at universities, sports performance centers, and some hospitals, with costs typically ranging from $40 to $75 per session.
3D Body Scanners
Optical 3D scanners capture your body’s shape using infrared sensors or cameras and estimate body fat from your surface geometry. You stand still for about 10 seconds in minimal clothing while the scanner creates a three-dimensional model. In validation studies comparing 3D scanning to underwater weighing, body fat percentage estimates were not significantly different between the two methods. However, accurate results require tight-fitting clothes and the ability to stand motionless and briefly hold your breath after exhaling.
Some gyms and wellness clinics now have these scanners, and a handful of consumer versions exist for home use. They’re useful for tracking body shape changes over time, since they also give you circumference measurements at dozens of sites.
How the Methods Compare on Accuracy
No body fat measurement is perfectly precise. Even DEXA, the clinical gold standard, has a margin of error of a few percentage points. When researchers compared DEXA to CT scans (which can directly visualize fat tissue), the two methods agreed closely on average, with differences well under 1% in most people. BIA showed much larger disagreements, with readings deviating from CT scans by as much as 15 to 22 percentage points in some individuals.
In practical terms, here’s how the methods stack up from most to least precise:
- DEXA scan: roughly 1 to 3% margin of error
- Hydrostatic weighing and Bod Pod: roughly 2 to 3% margin of error
- Skinfold calipers: roughly 3 to 5% with a skilled tester
- BIA scales and devices: roughly 3 to 8%, heavily influenced by hydration
- Tape measure formulas: roughly 3 to 5%, useful primarily for tracking trends
Getting Consistent Results Over Time
For most people, tracking the trend matters more than the absolute number. A smart scale that’s consistently off by 3% will still show you whether you’re gaining or losing fat, as long as you measure under the same conditions every time.
Whatever method you choose, control as many variables as possible. Measure in the morning before eating or drinking, after emptying your bladder. Wear the same clothing (or none). Use the same device, and if someone else is taking measurements, use the same person. Place scales on a hard, flat floor rather than carpet. For BIA devices specifically, avoid measuring after exercise or alcohol consumption, both of which alter your hydration and throw off the reading.
Measuring once a week or every two weeks gives you enough data points to spot a trend without getting distracted by the normal day-to-day fluctuations that every method produces.