Your waist measurement: how to take it and what it predicts

By Robert Robinson, founder of Neato Health · September 15, 2026 · 4 min read

A tape measure around your middle tells you more about your health than the scale does. Here is the evidence for the 'half your height' rule, how a waist becomes a body-fat estimate, and how to measure it the way the studies did.

BMI is a ratio of weight to height, and it cannot see where the weight sits. Two people with the same BMI can carry it as muscle on the legs or as fat around the organs, and the second is the one whose doctor should be concerned. The waist sees the difference. That is why a tape measure is one of the three numbers Neato tracks in the Body tab alongside weight and body fat, and why a good measurement is worth a minute of care.

Why the waist predicts risk

Fat stored around the abdominal organs, visceral fat, is metabolically different from fat under the skin. It is more strongly linked to insulin resistance, blood pressure, blood lipids and cardiovascular events. Waist circumference is the simplest proxy for it, and the World Health Organization’s 2008 expert consultation confirmed that it predicts these outcomes independently of BMI: for the same BMI, a larger waist means more risk.

Ashwell and Gibson took the idea one step further. In 2016 they analyzed the English national health survey and showed that a single ratio, waist divided by height, identified people with elevated cardiometabolic risk better than the standard BMI-plus-waist matrix, and did so with one rule for everyone: keep your waist under half your height. A 5′10″ person (70 inches) should have a waist under 35 inches. A 5′4″ person (64 inches), under 32. The rule holds across sexes and ethnic groups better than fixed waist thresholds do, because it scales with the person.

Neato uses that rule as its tape-measure target. If your waist is above half your height, the Body tab says so, and a fat-loss goal will bring it under.

Turning a waist into body fat

Precise body fat needs a DXA scan. But in 2018, Woolcott and Bergman showed that a formula using only height and waist predicts DXA-measured body fat better than BMI does. They called it relative fat mass:

They validated it on 12,581 adults from the U.S. national survey, where each person had both a tape measurement and a whole-body scan, and found it misclassified fewer people as obese or not obese than BMI did. It is not a scan; individual errors of several points are normal. But it is free, needs no scale, and follows your actual fat rather than your weight, which is why Neato uses it to estimate body fat when you enter a waist and have no other measurement.

How to measure it the way the studies did

Most people measure their waist wrong in the same way: they measure where their trousers sit. Trouser labels run small, and belts sit below the belly on many people, so a pants size understates the waist by 2 to 5 inches. The measurement the research uses is different, and it matters because both the half-your-height rule and the fat formula were built on it.

1. Find the top of your hip bones. Put your hands on your hips and press in; the bony ridge under your fingers is the iliac crest. The WHO protocol measures midway between that ridge and the bottom of the ribs; for most people that is at or just above the navel. Neato asks for the tape at the top of the hip bone, which is easier to find and close enough to be consistent.
2. Stand straight, feet together, arms at your sides. Breathe out normally and measure at the end of the exhale. Do not pull in.
3. Keep the tape level and snug, not tight. It should touch the skin all the way round without compressing it. Do it over bare skin or a thin shirt.
4. Measure twice and take the average if they differ by more than half an inch.
5. Same time of day. Morning, before eating, is the most repeatable. The waist grows through the day with food and water like the scale does.

How often, and what to expect

Once a week is enough. The waist moves slowly and the tape has a resolution of about half an inch, so daily measurements only show noise. Over a cut of a pound a week, the waist typically drops about a quarter to half an inch every two weeks, though it varies with where you carry fat. The useful signal is the direction over a month.

The waist is also the best check on a bulk, as the muscle guide explains. Weight rising while the waist stays flat means the gain is going where you want it. Weight and waist rising together means the surplus is too big.

Where Neato shows it

The Body tab tracks weight, body fat and waist on one chart so that the three can be read together. When the scale is up and the waist is down, you know what the scale is reporting. When body fat from a smart scale disagrees with body fat from the tape, the trend in either is still meaningful even when the levels disagree. And the half-your-height line sits on the waist chart, so you can see where the health threshold is without doing the arithmetic.

Neato’s guides are general wellness information built from the published research cited above. They are not a diagnosis, treatment, or medical advice, and they don’t know your history. For decisions about your health, talk to your doctor.