How to use it
- Under Units, pick Metric or US. Height and waist must be in the same unit system; the calculator converts for you.
- Enter your Height and your Waist, measured midway between the bottom of the ribs and the top of the hips after breathing out naturally.
- Optionally add Age and Weight. The classes are for adults, and NICE uses them for people with a BMI under 35, so the calculator checks both.
- Read your ratio, its class and half your height. Keep the result with Copy link, Save image or Share.
How the calculation works
The ratio is one division: waist-to-height ratio = waist ÷ height, with both in the same unit. Because the units cancel, the result is the same in centimeters or inches.
NICE's own example: a waist of 96.5 cm and a height of 170 cm give 96.5 ÷ 170 = 0.57. In inches, 38 ÷ 67 = 0.57 as well. Half of 170 cm is 85 cm, so that waist is 11.5 cm over half the height.
| Ratio | Class | What NICE says it indicates |
|---|---|---|
| 0.40–0.49 | Healthy central adiposity | no increased health risks |
| 0.50–0.59 | Increased central adiposity | increased health risks |
| 0.60 or more | High central adiposity | further increased health risks |
How accurate is this?
The division is exact; the measurement is where results go wrong. A tape that sits too low, too high or pulled tight changes the ratio. One centimeter on the waist moves the ratio by about 0.006 for someone 170 cm tall, so two careful measurements a few days apart are worth more than one quick one.
The classes are risk categories for groups, not a diagnosis. NICE lists type 2 diabetes, high blood pressure and cardiovascular disease among the risks linked to higher central adiposity. A ratio says nothing about any one person's health, and it is not made for pregnancy.
Why waist and not just weight
BMI uses only height and weight, so it can't tell where fat sits or whether weight is muscle. Fat around the middle is the part NICE calls central adiposity. That is why NICE suggests measuring waist-to-height ratio alongside BMI for adults with a BMI under 35, and says the classes can be used for both sexes, all ethnicities and adults with high muscle mass.
Your BMI is on the BMI calculator. For a body fat estimate from tape measurements, try the body fat calculator.
Who the classes are for
The adult classes are for people aged 18 and over with a BMI under 35; NICE recommends the waist-to-height measurement for adults below that BMI. For children and young people aged 5 and over, NICE has separate recommendations and points to the NHS waist-to-height ratio calculator.
Questions
- What is a good waist-to-height ratio?
- In NICE's adult classes, 0.4 to 0.49 is called healthy central adiposity. In plain terms: a waist less than half your height.
- Do I use centimeters or inches?
- Either, as long as both measurements use the same one. The ratio is identical: 96.5 cm ÷ 170 cm and 38 in ÷ 67 in both give 0.57.
- Where exactly do I measure my waist?
- NICE's method: find the bottom of your ribs and the top of your hips, wrap the tape midway between them (usually just above the belly button) and breathe out naturally before reading it.
- Is it the same for men and women?
- Yes. NICE uses the same classes for both sexes and all ethnicities.
- Is anything I type sent to a server?
- No. The math runs in your browser. Copy link puts the numbers after a # in the link, a part that browsers don't send to servers.