You can calculate your body fat percentage at home using nothing more than a tape measure and a simple formula. The most widely used approach is the U.S. Navy method, which estimates body fat from circumference measurements of your neck, waist, and (for women) hips. Other methods use your BMI, skinfold calipers, or just your height and waist. Each has tradeoffs in accuracy and convenience.
The U.S. Navy Method
This is the go-to formula for estimating body fat without specialized equipment. You need a flexible tape measure, a calculator with a log function (or an online calculator), and your height in inches.
For men, measure two sites: your neck at its narrowest point just below the Adam’s apple, and your waist at the navel. The formula is:
Body fat % = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
For women, measure three sites: neck, waist at the narrowest point above your hip bones, and hips at the widest point of the glutes with feet together. The formula is:
Body fat % = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
All measurements are in inches. Compared to DEXA scans (the gold standard for body composition), the Navy method has a standard error of about 3.4 percentage points for men and 4.2 percentage points for women. That means if the formula says you’re at 20% body fat, your true value is likely somewhere between roughly 16% and 24%. It’s useful for tracking trends over time, even if the absolute number isn’t perfectly precise.
How to Take Accurate Measurements
Sloppy tape placement is the fastest way to get a misleading result. Stand upright and relaxed for every measurement. Wrap the tape horizontally, keeping it snug against your skin without compressing it. Measure your waist just after you breathe out normally, not while sucking in. Place the tape just above your hip bones, which for most men lands right at the navel.
For your neck, position the tape at the base of the neck, just below the Adam’s apple, at the narrowest point above the trapezius muscles. For hip measurements, stand with your feet together and measure at the widest part of your glutes. Take each measurement twice and use the average. Even half an inch of difference in your waist reading can shift the result by a full percentage point.
The Relative Fat Mass Method
If logarithms feel like too much math, the Relative Fat Mass (RFM) formula developed by researchers at Cedars-Sinai is simpler. You only need your height and waist circumference, measured in the same unit.
Men: RFM = 64 − (20 × height ÷ waist circumference)
Women: RFM = 76 − (20 × height ÷ waist circumference)
So a man who is 70 inches tall with a 34-inch waist would calculate: 64 − (20 × 70 ÷ 34) = 64 − 41.2 = 22.8% body fat. The result approximates your body fat percentage. Because it’s a simple ratio, you can use inches, centimeters, or any unit as long as both measurements match.
The BMI-Based Approach
If you already know your BMI, several published formulas convert it to an estimated body fat percentage using your age and sex. The most commonly cited is the Deurenberg formula:
Body fat % = (1.20 × BMI) + (0.23 × age) − (10.8 × gender) − 5.4
For gender, plug in 1 for male and 0 for female. A 35-year-old man with a BMI of 26 would get: (1.20 × 26) + (0.23 × 35) − (10.8 × 1) − 5.4 = 31.2 + 8.05 − 10.8 − 5.4 = 23.05%.
This approach is the easiest to calculate, but it’s also the least accurate for individuals. BMI doesn’t distinguish between muscle and fat, so someone who lifts weights regularly will get an inflated reading. It works better for population-level estimates than for any one person.
Skinfold Calipers
Skinfold testing uses calipers to pinch and measure the thickness of fat beneath the skin at specific body sites. The most common protocol is the Jackson-Pollock 3-site test. For men, the three sites are the chest, abdomen, and thigh. For women, the sites are the triceps (back of the upper arm), suprailiac (just above the hip bone), and thigh.
You add the three skinfold measurements together, then plug the sum into a body density equation that accounts for age. Body density then converts to body fat percentage. The math is cumbersome by hand, which is why most people use an online calculator or a chart that came with their calipers. The bigger practical challenge is technique. Skinfold accuracy depends heavily on pinching at the exact right spot and applying consistent pressure. If you test yourself, practice several times until you get repeatable readings. Having someone else take the measurements usually improves consistency.
Smart Scales and BIA Devices
Bioelectrical impedance analysis (BIA) scales send a small electrical current through your body and estimate fat mass based on how quickly the signal travels. Muscle and water conduct electricity well; fat does not. These scales are convenient, but their readings fluctuate based on hydration levels, whether you’ve eaten recently, skin temperature, body position, and how much you’ve exercised that day.
For the most consistent readings, step on the scale at the same time each morning, before eating or drinking, and not immediately after a workout. Even then, treat the number as a rough trend tracker rather than a precise measurement. Day-to-day swings of 2 to 3 percentage points are common and don’t reflect actual changes in body fat.
What the Numbers Mean
Once you have a number, you need context. The American Council on Exercise classifies body fat percentage into ranges for men and women:
- Essential fat: 2–5% for men, 10–13% for women. This is the minimum your body needs to function. Staying here long-term is neither realistic nor healthy for most people.
- Athletes: 6–13% for men, 14–20% for women.
- Fitness: 14–17% for men, 21–24% for women.
- Average: 18–24% for men, 25–31% for women.
- Obese: above 25% for men, above 32% for women.
These ranges are guidelines, not hard cutoffs. Where you fall within “average” or “fitness” matters less than whether your body fat is trending in the direction you want over weeks and months.
Which Method Should You Use
If you want a quick, reasonable estimate and own a tape measure, the U.S. Navy method or the RFM formula are your best options. The Navy method has the most validation research behind it. The RFM formula is easier to calculate and requires one fewer measurement for women.
If you’re tracking progress over time, consistency matters more than the method you choose. Pick one approach, measure under the same conditions each time (same time of day, same meal timing, same person taking the measurement), and compare your numbers week to week. A 3-point drop over two months is meaningful regardless of whether your starting number was perfectly accurate. Chasing a precise absolute number matters far less than knowing which direction you’re heading.