Body fat percentage tells you what your weight is made of, which is the question the scale cannot answer. Every method of measuring it involves a trade between accuracy, cost and convenience, and none of the affordable ones are as precise as their displays suggest.
Skinfold calipers
You pinch the fat at several points on the body, measure the thickness of each fold, and feed the numbers into an equation.
Calipers are cheap and they travel. In trained hands, taking the same sites the same way each time, they track change well.
In untrained hands they are erratic. Pinch depth, site location and how hard you squeeze all move the result, and the same person measuring you twice can produce different numbers. They also get less reliable at higher body fat levels, where the folds are too thick to pinch cleanly. If you use them, have the same person do it every time.
Bioelectrical impedance
This is what your bathroom scale uses. A small current passes through you, and since fat resists electricity more than lean tissue does, the device infers your composition from that resistance.
The convenience is unbeatable and the accuracy is mediocre. Hydration moves the result, so a reading after a salty dinner and one after a hard session will disagree despite nothing having changed. So does a recent meal, and so does exercise in the hours before.
A cheap scale can still be useful if you standardise the conditions: same time of morning, before food or drink, after the toilet. Ignore the absolute figure. Watch the direction over weeks.
DEXA scans
A DEXA scan uses low-dose X-rays and reports fat mass, lean mass and bone density, with a regional breakdown showing where the fat actually sits. It is the closest thing to a reference standard that a normal person can book.
The catch is cost and access. Not everyone lives near a facility that offers it, and the price makes frequent scans impractical. There is also variation between machines, so comparing a scan from one clinic to a scan from another is not a fair comparison.
Two scans a year, at the start and end of a serious phase, is a sensible use of it.
Hydrostatic weighing
You are weighed underwater to work out your body density, and body fat is calculated from that. It is very accurate and it involves being submerged after exhaling everything in your lungs, which people generally do not enjoy twice.
Access is the real barrier. Few facilities still offer it, and DEXA has largely taken over.
The one that matters most
Here is the uncomfortable truth about all of them. The absolute number is less useful than the trend, and the trend is only meaningful if you keep the method constant.
Two devices will disagree with each other by several percentage points on the same body on the same day. That does not mean one is lying. It means you should pick a method, standardise the conditions, and stop cross-comparing.
Photographs in consistent lighting are underrated for the same job, and a tape measure around the waist is free. Our comparison of waist-to-height ratio and BMI covers why that simple measurement holds up so well.
Setting a target you can actually hit
Fat loss of half to one percent of body fat per month is a reasonable pace and slower than most people expect. Faster than that usually means muscle is going too.
Pick a range rather than a point. And be aware that going very lean has costs, particularly for women, where hormonal function suffers well before the number looks impressive.
If you are trying to lose fat and hold muscle at the same time, the calorie side matters more than the measuring. Start with your maintenance calories, keep protein high, and keep lifting. The measurement only tells you whether it is working.