The "half your height" rule
The Ashwell / NHS guideline: your waist should measure less than 50% of your height. For a 5'5" (65-inch) woman, that's under 32.5 inches. For 5'9" (69 inches), that's under 34.5 inches.
This ratio predicts cardiovascular and diabetes risk better than BMI alone, especially for people whose weight sits mostly around the middle.
How to measure
Stand relaxed. Measure just above your belly button, around the narrowest part of your torso. Don't suck in. A soft tape is best.
If tape isn't handy, a well-fitting belt size in inches is a close-enough proxy.
