If you only measure one thing, measure your waist. It predicts cardiometabolic risk better than BMI, it takes one tape measure, and unlike BMI it can tell the difference between muscle and fat.
Waist Ratios
Waist-to-height and waist-to-hip — often a sharper health read than BMI alone.
Methods: waist-to-height ratio with the 0.5 boundary (NICE guidance: keep your waist under half your height). Absolute waist limits follow WHO cut-points — 94 cm / 37 in for men and 80 cm / 31.5 in for women as the first warning line, 102 cm / 40 in and 88 cm / 35 in as the second. Waist-to-hip bands use the common three-tier convention; note that WHO treats a ratio at or above 0.90 (men) or 0.85 (women) as abdominal obesity in its own right, so a male reading in the 0.90–0.99 band has already crossed that line.
Estimates only — general education, not medical advice. Talk with your doctor before changing how you eat or train. More tools at whatshouldiweigh.com.
Keep your waist under half your height
That’s the whole rule. Waist-to-height ratio below 0.5.
It works across adult heights and body types without adjustment, which is unusual for a health metric. A 6-foot man should keep his waist under 36 inches; a 5-foot-4 woman under 32.
| Ratio | Reading |
|---|---|
| Under 0.4 | Lean — possibly underweight |
| 0.4 – 0.49 | Healthy |
| 0.5 – 0.59 | Increased risk |
| 0.6 and above | High risk |
The UK’s National Institute for Health and Care Excellence now recommends waist-to-height ratio alongside BMI in its obesity guidance, specifically because it captures central fat that BMI misses.
Why waist size matters more than total weight
Fat isn’t uniform in its effects. Where it sits changes what it does.
Subcutaneous fat sits under the skin — hips, thighs, upper arms. Metabolically fairly quiet.
Visceral fat packs around the organs inside the abdomen. It’s metabolically active in unhelpful ways: it releases inflammatory signals and free fatty acids directly into the portal circulation feeding the liver, and it’s strongly associated with insulin resistance, type 2 diabetes, high blood pressure and cardiovascular disease.
A waist measurement is a rough but genuine proxy for visceral fat. Two people at the same weight and BMI with different waist measurements have different risk profiles, and the tape catches what the scale can’t.
Absolute waist thresholds
Alongside the ratio, the WHO sets straight circumference limits:
| Increased risk | Substantially increased | |
|---|---|---|
| Men | Over 94 cm / 37 in | Over 102 cm / 40 in |
| Women | Over 80 cm / 31.5 in | Over 88 cm / 35 in |
Worth noting these were derived largely from European populations. Risk tends to begin at lower thresholds in South Asian, Chinese and Japanese populations, and several countries publish their own lower cut-points.
Waist-to-hip ratio
The second number the calculator gives you. Waist divided by hip circumference, which describes fat distribution rather than amount.
The WHO treats 0.90 or above in men and 0.85 or above in women as abdominal obesity. The calculator’s bands use the common three-tier convention, so a man reading between 0.90 and 0.99 shows as “moderate” — but he has already crossed the WHO line, which is worth knowing.
Waist-to-height is generally the more useful of the two. Waist-to-hip can be misleading in people with naturally narrow or broad hips, since it moves when the denominator changes rather than when anything about your health does.
Measuring it properly
Technique matters more than the arithmetic here.
- Stand relaxed, feet together, at the end of a normal breath — don’t hold it, don’t brace, don’t pull your stomach in
- Tape at the navel for men, the narrowest point for women
- Keep the tape horizontal all the way round; check in a mirror
- Snug against skin without compressing
- Measure three times and average
- Same time of day, ideally morning before eating
A one-inch error changes the ratio by about 0.015 — enough to move you across a band boundary.
What actually shrinks it
Visceral fat responds well to modest, consistent change — better than subcutaneous fat does, and often faster than people expect. There’s no way to target it directly; spot reduction doesn’t exist. But a moderate calorie deficit, regular activity of almost any kind, adequate sleep and reduced alcohol all reduce it, and the waist is usually where early progress shows first.
Common questions
Is waist-to-height better than BMI? For predicting cardiometabolic risk, generally yes. It picks up central fat and isn’t fooled by muscle. Using both, plus a body fat estimate, beats either alone.
Where exactly is my waist? For this measurement, at the navel for men and the narrowest point of the torso for women. Not where your trousers sit.
My BMI is high but my waist ratio is fine. Which do I trust? Usually that pattern means you carry more muscle than average, and the waist ratio is the more informative of the two. If both are high, that’s worth acting on.
Does it work for children? The 0.5 threshold has been studied in children and performs reasonably, but paediatric assessment properly uses age-and-sex percentile charts. Ask a paediatrician rather than an adult calculator.
How often should I measure? Every two to four weeks. It moves slowly, and weekly measurement mostly captures noise.
The calculators on this site are educational estimates, not medical advice. Talk with your doctor about your cardiometabolic risk — a waist measurement is one input among blood pressure, blood lipids and glucose.