Waist-to-height ratio

What it's for

The waist-to-height ratio is an indicator of belly fat often more reliable than BMI alone. The simple rule: your waist should be less than half your height (ratio < 0.5).

How to measure

Measure the waist at navel level, relaxed, and height in the same unit. Not a diagnosis: for health assessments see your doctor.

Why it says more than weight

Weight, and BMI with it, doesn't know where the fat is, and on that the difference is large: fat under the skin of hips and thighs is nearly inert, while fat around the abdominal organs is metabolically active and is much more closely associated with diabetes and cardiovascular problems. Waist measurement captures it directly, which is why two people with the same BMI can carry very different risks.

Relating it to height instead of using it alone serves one precise purpose: it makes the number comparable between tall and short people, and between men and women, without separate tables. The rule fits in one sentence — your waist should be less than half your height — and it holds identically for all adults.

How to measure it, which is where it goes wrong

The tape must be held horizontal, snug but not tight, and the measurement is taken at the end of a normal breath out, not holding your breath and not pulling your stomach in. The point is halfway between the lowest rib and the top of the hip bone, which on most people is just above the navel.

Better in the morning before eating, and always the same way: what counts isn't the isolated value but the comparison over time, and two measurements taken in different conditions can't be compared. A couple of centimetres of difference between two readings is entirely normal, and isn't a result.

The bands, and what it doesn't say

Below 0.4 the waist is very small (in extreme cases too small); between 0.4 and 0.5 is the band where most people are fine; from 0.5 upwards excess abdominal fat begins and from 0.6 the risk is considered high. These thresholds are for adults: in children and adolescents age curves are used, and in pregnancy the measure makes no sense.

Like every index, it isn't a diagnosis: it doesn't tell fat from muscle and it doesn't know the history of whoever uses it. It's a signal, and the useful thing it can do is get you to take a number to the doctor instead of a feeling.

Nearby tools

For weight against height there is BMI calculator, and for an estimate of the fat percentage Body fat. For daily requirements Basal metabolic rate, and for blood pressure Blood pressure values.