How to measure body fat at home (and which method to trust)

Accuracy versus consistency

Every home method has error. A tape or caliper estimate might be 3 or 4 percentage points off your true value. That sounds bad, but if the error is roughly the same each time, the trend is still reliable.

So the goal is not a perfect number. It is to pick one method, measure the same way under the same conditions, and watch the direction over weeks. Switching methods makes the numbers impossible to compare.

The methods compared

Error ranges are approximate and depend heavily on technique, the device and the individual. Even DEXA, often treated as the gold standard, varies between machines and with hydration.

Method 1: the tape measure

The US Navy method estimates body fat from height and a few circumferences. It needs only a flexible tape and two minutes, and our body fat calculator does the maths.

1. Neck: measure just below the Adam's apple, tape sloping slightly down at the front.
2. Waist (men): horizontally at the level of the navel.
3. Waist (women): at the narrowest point, usually just above the navel.
4. Hips (women): at the widest point of the buttocks.
5. Take each measurement three times and use the average.

Keep the tape snug but not compressing the skin, stand relaxed and measure at the end of a normal breath out. Do not suck in. Its weakness: people who carry fat mainly on the hips or legs, or who have very thick necks from training, can be misestimated.

Method 2: skinfold calipers

Calipers pinch a fold of skin and fat at set sites and measure its thickness. Formulas such as Jackson-Pollock then estimate total body fat. A 3-site or 7-site test is most common.

• Men, 3-site: chest, abdomen, thigh
• Women, 3-site: triceps, suprailiac (above the hip bone), thigh

Measure on the right side of the body, pinch the fold firmly between thumb and finger, place the caliper about 1 cm away, and read after two seconds. Take two or three readings per site.

Calipers work well for lean people and for tracking individual sites over time. They are harder to use on yourself, so ask the same person to measure you each time if possible. In people with higher body fat, folds can be too thick to measure reliably.

Method 3: smart scales (bioelectrical impedance)

Smart scales send a small, harmless current through your body. Fat conducts electricity less well than water-rich lean tissue, so the resistance is used to estimate body fat.

The catch is that the reading depends heavily on hydration. A large drink, a salty meal, a workout or a hot shower can shift the result by several percentage points in a day. Foot-only scales mainly read your lower body.

Use them for the long-term average, not the daily number. Weigh at the same time each morning after using the bathroom and before eating or drinking, then look at the weekly average. People with pacemakers or other implanted devices should not use BIA scales, and they are generally not recommended during pregnancy.

Method 4: progress photos

Photos cannot give you a percentage, but they are often the most motivating record of change, because day-to-day you see yourself too often to notice it.

• Same place, same lighting, same time of day
• Front, side and back, relaxed and flexed
• Phone at the same height and distance each time
• Every 2 to 4 weeks is enough

How often to measure, and mistakes to avoid

Body fat changes slowly. Losing 0.5 kg (1 lb) of fat a week moves body fat percentage by roughly half a point per week for many people, which is inside the error of most methods. Measuring daily mostly records noise.

• Changing the time of day. You are taller and lighter in the morning, and your waist grows after meals. Always measure first thing, before eating.
• Measuring after training. Muscles are pumped and fluid shifts for hours. Wait until the next morning.
• Pulling the tape tight. Compressing the skin shaves centimetres off. Snug, not squeezing.
• Moving the landmarks. Measure the waist at the navel every time, not wherever looks smallest.
• Ignoring the menstrual cycle. Water retention can add 1 to 2 kg and change tape and BIA readings. Compare the same point in your cycle month to month.
• Reacting to one reading. Decide only on trends across at least three measurements.

Example: tracking a 12-week cut

Here is what realistic numbers look like for someone who starts at 85 kg (187 lb) and around 24 percent body fat, losing about 0.5 kg a week while lifting three times weekly.

Notice that individual readings wobble: lean mass appears to dip then recover, which is measurement noise. The overall picture is clear, though: about 6 kg lost, almost all of it fat, and a 7 cm smaller waist. That is a successful cut, even if no single number was perfect.

When the scale and tape disagree

Sometimes your weight stays flat while your waist shrinks, or the scale drops but the mirror looks the same. Here is how to read it:

Give any surprising reading two weeks before acting on it. If you are deliberately trying to lose fat and build muscle together, read the body recomposition guide.

What to do with your number

A body fat estimate is more useful than BMI for people who lift, because BMI cannot tell muscle from fat. Use your result to:

• Work out lean mass with the lean body mass calculator
• Check how muscular you are relative to height with the FFMI calculator
• Set a goal weight: lean mass divided by (1 minus target body fat fraction)
• Decide between a cut or a bulk; see bulking vs cutting

Rough healthy ranges for adults are about 10 to 22 percent for men and 20 to 32 percent for women, varying with age. Very low levels are not healthier and can disrupt hormones, especially in women.

If you notice yourself measuring obsessively, or the numbers are affecting how you eat or feel about yourself, take a break from tracking and consider speaking to a doctor. Progress photos and training performance are perfectly good ways to judge progress.