Why body fat beats the bathroom scale
Weight and BMI tell you how much you are; body-fat percentage tells you what that weight is made of. It's the difference that matters most for a muscular person mislabelled "overweight" by BMI, and for someone at a "normal" weight who's actually carrying very little muscle. Skinfold calipers are the classic home-and-clinic tool for estimating it: you pinch the fat just under the skin at set sites, feed the millimetres into a validated equation, and get a defensible estimate for a few dollars of equipment.
The methods the Chonkometer offers
All three of these convert your skinfolds into body density, then into fat percentage using the Siri equation (BF% = 495 ÷ density − 450).
Durnin & Womersley (4 sites)
Biceps, triceps, subscapular and suprailiac. This method sums all four, takes a logarithm, and uses age- and sex-banded constants — which makes it forgiving and widely applicable across ages. A solid default if you're not sure which to pick.
Jackson-Pollock (3 sites)
The fast one. For men it uses chest, abdomen and thigh; for women, triceps, suprailiac and thigh. Fewer pinches, quicker reading, and very widely used in gyms — accurate enough for tracking change over time.
Jackson-Pollock (7 sites)
Chest, midaxillary, triceps, subscapular, abdomen, suprailiac and thigh. More sites means more consistency and less reliance on any single measurement, at the cost of more pinching. The choice for the most careful home estimate.
Note on methods: we've deliberately left out the Parrillo caliper method for now, because its published site list varies between sources and we won't ship a formula we can't stand behind. Numbers here are only worth having if they're defensible.
How to pinch properly
Skinfolds are technique-sensitive — this is where most of the error lives. Always measure the right side of the body. Pinch a firm fold of skin and fat (not muscle) about a centimetre from where the caliper jaws will sit, apply the caliper, wait one to two seconds, and read. Take each site two or three times and use the average, and try to measure at the same time of day in the same condition (hydration and recent exercise shift the readings). Consistency matters more than any single perfect pinch — the same person measuring you the same way each time gives the most trustworthy trend.
What the number can and can't do
Skinfold estimates carry a real margin of error — commonly a few percentage points versus a lab method like DEXA or hydrostatic weighing — because they infer whole-body fat from a handful of surface pinches. They're excellent for tracking change in one person over time, and rougher as an absolute one-off truth. If you want a gold-standard number, a DEXA scan is the tool. If you just want to know whether a "high" BMI is muscle or fat, a careful skinfold reading usually answers it well enough. Pair this with your BMI and waist for the full picture.
When the number is worth a doctor
A genuinely high body-fat estimate — especially with a large waist — is a reasonable prompt for a conversation with a professional who can measure properly and look at the rest of your health. And a very low estimate isn't a prize: dropping below the essential-fat range carries its own risks, particularly for hormonal health. The Chonkometer flags both ends kindly and leaves the medicine to the medics.