You can calculate your body fat percentage at home using nothing more than a tape measure, or you can get a more precise reading with calipers, a smart scale, or a clinical scan. Each method trades convenience for accuracy, so the best choice depends on whether you need a rough estimate or a precise number. Here’s how each method works, what the formulas look like, and what the results actually mean.
The Tape Measure Method (U.S. Navy Formula)
The simplest approach requires a flexible tape measure and about two minutes. The U.S. Navy developed circumference-based formulas that estimate body fat from the relationship between your neck, waist, hips, and height. Men need two measurements; women need three.
What to Measure
- Neck: Wrap the tape around the base of your neck, just below the Adam’s apple, at the narrowest point above the trapezius muscles.
- Waist: Measure at the narrowest point above your hip bones. For most men this is at the navel; for women it varies.
- Hips (women only): Stand with feet together and measure at the widest point of your glutes.
The Formulas
For men: Body fat (%) = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. All measurements in inches.
For women: Body fat (%) = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. Again, all in inches.
You don’t need to do this math by hand. Dozens of free online calculators plug these numbers in for you. The value of knowing the formula is understanding what drives it: the ratio of your midsection to your frame size. A larger waist relative to your neck and height pushes the estimate up. This method is accurate enough for general tracking, typically within 3 to 4 percentage points of clinical measurements, but it can underestimate fat in people who carry weight in unusual patterns.
Skinfold Calipers
Calipers measure the thickness of pinched skin folds at specific spots on your body. The idea is straightforward: the thicker the fold, the more subcutaneous fat sits beneath the skin at that site. A basic plastic caliper costs under $10, though higher-quality metal ones run $20 to $40.
The most widely used protocol is the Jackson-Pollock method, which comes in a 3-site and 7-site version. The 7-site test measures skinfolds at the chest, abdomen, thigh, tricep (back of the upper arm), subscapular (just below the shoulder blade), suprailiac (just above the hip bone), and midaxillary (mid-rib cage on the side). The 3-site version uses a subset of those locations, with different sites for men and women. You plug the sum of your skinfold measurements, along with your age and sex, into a body density equation, then convert that to a body fat percentage.
How to Take a Skinfold Reading
Always measure on the same side of your body, typically the right. Using your thumb and index finger, lift a fold of skin away from the underlying muscle. Place the caliper jaws about half an inch below your fingers, release your grip on the caliper (but keep holding the skin fold), and read the measurement within five seconds. After five seconds, the caliper compresses the tissue and the reading drifts lower. Take two or three readings at each site and average them.
Consistency matters more than perfection. If the same person measures you in the same way each time, the readings will reliably track changes over weeks and months, even if the absolute number is a few points off. Research comparing skinfold estimates to gold-standard four-compartment models found errors ranging from about 1 to 5 percentage points depending on which equation was used and who was doing the measuring. The biggest source of error isn’t the formula; it’s the pinch technique.
Smart Scales and Handheld Devices (BIA)
Bioelectrical impedance analysis, or BIA, is the technology inside smart bathroom scales and handheld body composition devices. It sends a weak electrical current through your body and measures how quickly the signal travels. Fat tissue resists the current more than muscle and water, so the device estimates your fat mass based on that resistance.
BIA is the most convenient option, but it’s also the most temperamental. The reading shifts based on how hydrated you are, when you last ate, your skin temperature, and even where the electrodes contact your body. A glass of water, a hot shower, or a workout can each move the number by a couple of percentage points. The device also assumes a uniform current pathway through your tissues, which isn’t how electricity actually behaves in a human body. Standardized protocols (measuring first thing in the morning, fasted, at a consistent hydration level) help, but even under ideal conditions BIA tends to be less precise than calipers or clinical scans.
That said, if you weigh yourself on the same scale at the same time every morning, the trend line over weeks is useful. Don’t fixate on any single reading.
Clinical Methods: DEXA Scans
Dual-energy X-ray absorptiometry, commonly called a DEXA scan, is the most accessible clinical option. You lie on a table while a low-dose X-ray beam passes over your body, differentiating bone, lean tissue, and fat. The scan takes about 10 minutes, costs $50 to $150 at most body composition clinics, and gives you a regional breakdown showing where fat is distributed.
DEXA is often called the gold standard, though it does have a margin of error. Research puts its standard error of estimate around 3% body fat when compared to four-compartment models, which combine underwater weighing, DEXA, and other measurements for the most precise result possible. For most people, a DEXA scan every three to six months provides a reliable anchor point that you can supplement with cheaper methods in between.
The Waist-to-Height Ratio Shortcut
If you don’t need an exact body fat percentage and simply want to know whether your fat levels pose a health risk, the waist-to-height ratio is remarkably useful. Divide your waist circumference by your height, both in the same units. According to NHS guidelines, your waist should be less than half your height, meaning a ratio below 0.5. Above that threshold, you’re carrying excess abdominal fat, which correlates strongly with metabolic risk regardless of what you weigh.
This single number won’t tell you whether you’re at 22% or 28% body fat, but it captures the type of fat that matters most for heart disease, diabetes, and other metabolic conditions. It takes ten seconds, requires no equipment beyond a tape measure, and outperforms BMI for identifying visceral fat risk.
What the Numbers Mean
Body fat percentage norms differ substantially between men and women because women carry essential fat in breast tissue, reproductive organs, and around the hips. The American Council on Exercise classifies body fat ranges as follows:
- Essential fat: 2 to 5% for men, 10 to 13% for women. Below these levels, hormonal and organ function is compromised.
- Athletes: 6 to 13% for men, 14 to 20% for women.
- Fitness: 14 to 17% for men, 21 to 24% for women.
- Average: 18 to 24% for men, 25 to 31% for women.
- Above average range: 25%+ for men, 32%+ for women.
Dropping below 6% for men or 14% for women is considered potentially dangerous and is rarely sustainable outside of competition-day conditions for bodybuilders or physique athletes.
How Age Changes the Picture
These ranges shift as you get older. Muscle mass naturally declines with age, which means even if your weight stays the same, your body fat percentage creeps upward. Adults over 60 tend to carry higher body fat percentages than younger adults at the same health status. This combination of rising fat mass and falling muscle mass is sometimes called sarcopenic obesity, and it’s one reason body fat percentage is a better health marker than body weight alone in older adults.
Clinical Thresholds for Metabolic Risk
A 2025 study published in the Journal of Clinical Endocrinology & Metabolism proposed body-fat-based definitions for overweight and obesity that align with actual metabolic risk. The cutoffs: overweight begins at 25% body fat for men and 36% for women, while obesity begins at 30% for men and 42% for women. Notably, no men in the study showed signs of metabolic syndrome below 18% body fat, and no women showed signs below 30%. These thresholds offer a more physiologically meaningful picture than BMI, which can’t distinguish between muscle and fat.
Choosing the Right Method
For most people, the best approach combines a cheap method for frequent tracking with an occasional clinical measurement for calibration. Use the Navy formula or a BIA scale weekly to watch trends. Get a DEXA scan once or twice a year if you want a precise baseline. If you’re working with a trainer, skinfold calipers measured by the same person each time provide reliable tracking that’s more granular than tape measurements.
No method is perfectly accurate. Every technique estimates body fat through indirect measurements, and each carries its own 2 to 5 percentage point margin of error. What matters more than any single number is the direction you’re moving over time. Pick one method, standardize your conditions (same time of day, same hydration status, same person taking measurements), and track consistently.