Where you carry weight matters, not only how much of it there is. This compares your waist measurement with the threshold the National Heart, Lung, and Blood Institute publishes, and tells you how far above or below it you are.
Key terms
- Waist circumference — measured around the bare abdomen, just above the hip bone, after breathing out. Not your trouser size, which is usually smaller.
- The threshold — more than 35 inches for women, more than 40 inches for men. Above it, NHLBI says risk increases.
- Abdominal fat — fat around the organs rather than under the skin. It is the reason waist size carries information that weight alone does not.
How it works
There is no formula here, and pretending otherwise would be dressing a comparison up as a calculation. Your measurement is compared with a published figure.
NHLBI thresholds
women: more than 35 in (88.9 cm) · men: more than 40 in (101.6 cm)
A metric measurement is converted using the exact definition of an inch, so the boundary sits precisely where NHLBI put it rather than at a rounded 89 or 102 cm.
“More than” is read literally: exactly 40 inches is at the threshold, not above it. Flagging the boundary value itself would be stricter than the guidance being cited.
How to measure properly
Most of the error in this number comes from the measuring, not the maths. Put the tape against skin rather than over clothing, level all the way round, just above the hip bone. Breathe out and relax — pulling your stomach in produces a smaller number and tells you nothing. Take it twice; if the two readings disagree by more than half an inch, take a third.
What this does not tell you
It is one measurement against one threshold. It does not know your muscle, your build, your blood pressure or your family history, and a single number either side of a line does not make anyone healthy or unhealthy. The threshold exists as a prompt for a conversation with a doctor, not as a verdict. It applies to adults rather than children, and it is not meaningful during pregnancy.
How to use this calculator
- Pick metric or imperial and choose which threshold applies to you.
- Enter the measurement taken as described above.
- Read the difference rather than only the pill — an inch either side of the line is nothing like a foot.
- Measure again in a few months. The trend over time is worth far more than any single reading.
Frequently asked questions
Where exactly do I put the tape?
Just above the hip bone, level all the way around, against bare skin. Not at the narrowest point of your torso, and not where your trousers sit — both give a different number from the one the threshold was built on.
Why are the thresholds different for men and women?
Body fat distributes differently on average, so the same waist measurement carries a different meaning. NHLBI publishes 35 inches for women and 40 for men for that reason.
My BMI is fine but my waist is above the threshold. Which counts?
Both, and they answer different questions. BMI is about overall weight for height; waist size is about where that weight sits. It is entirely possible to sit in the healthy BMI range and still carry enough abdominal fat to be worth discussing with a doctor.
Does this apply to children or during pregnancy?
No. The threshold is for adults, and it has no meaning in pregnancy. Children are assessed on growth charts by age and sex instead.
How quickly does waist size change?
Slowly, and not in a straight line. Day-to-day readings move with food, fluid and the time of day, which is why measuring every few months under the same conditions tells you far more than measuring every week.
