What it means
The NHLBI says a waist of more than 35 inches for women or more than 40 inches for men increases health risk. Lower cutoffs may apply for some racial and ethnic groups, since risk at a given waist size differs.
To measure, stand up straight, place a tape measure around your bare belly just above your hip bones, keep it snug but not pressing into the skin and measure after breathing out normally. Measure at the same time of day each time, ideally in the morning.
Waist size reflects visceral fat better than BMI does. It is one of the five features of metabolic syndrome and can add information when BMI is borderline.
During weight loss, a shrinking waist can show progress when the scale stalls, especially for people who are also building muscle.
Why it matters
Waist size is a cheap, repeatable way to track belly fat loss alongside weight on a GLP-1.