- In the morning, before breakfast, undressed.
- Find the top of your hip bone at the side (the iliac crest) and place the tape there, level all the way round.
- Snug, not pressing into the skin.
- Breathe out normally and read at the end of the breath.
- Measure twice; if the two differ by more than a centimeter, measure a third time.
- Enter the average, dated.
- Hip: tape level at the widest point of the buttocks, same rules.
- Every two to four weeks.
Why that site
Two sites are in common use. The World Health Organization's protocol measures midway between the lowest rib and the top of the hip bone (WHO 2011); the US national survey whose data sit behind Vitality Tracker's metabolic age measures at the top of the hip bone itself, at the end of a normal breath out, with the tape horizontal (Fryar 2021). The two differ by a few centimeters on many bodies, in either direction depending on shape. VT uses the hip-bone site so that your waist is on the same basis as the reference it is compared with, and because the hip bone is easier to find the same way twice than a midpoint. Whichever you use, use it every time: at the metabolic age's sensitivity of about a third of a year per centimeter, a change of site is worth about a year.
Why the tape matters more than the scale here
No scale measures central fat; the visceral-fat index is an estimate from the trunk's impedance that tracks belly fat loosely at best (Browning 2010). A tape at the waist is the better home measure, and the waist-to-height ratio built from it is the central-fat measure VT scores on.
What moves the reading, apart from fat
A meal, bloating, posture, breathing in, a tape pulled tight, and clothing. The morning routine removes most of it; the two measurements and the average remove the rest.
How Vitality Tracker uses it
The waist feeds the waist-to-height and waist-to-hip ratios, the Vitality Score's central-fat term and the metabolic age. The entry is dated, VT prompts for a fresh one when the stored waist is about a month old, and a tape that connects to the app writes directly into the same series as a typed entry from the same tape, while entries from different tapes are kept apart.
Sources
- World Health Organization. Waist circumference and waist–hip ratio: report of a WHO expert consultation, Geneva, 8–11 December 2008. WHO, 2011
- Fryar CD, Carroll MD, Gu Q, Afful J, Ogden CL. Anthropometric reference data for children and adults: United States, 2015–2018. NCHS Vital Health Stat 3(46), 2021
- Browning LM, et al. Validity of a new abdominal bioelectrical impedance device to measure abdominal and visceral fat: comparison with MRI. Obesity 2010;18:2385–91. doi:10.1038/oby.2010.71
- Vitality Tracker, Metabolic age method (S-AnthropoAge), October 2026.