BMI vs waist-to-height ratio: which measure tells you more?

Key takeaways - BMI compares weight with height. It is a useful first screen, but it cannot tell fat from muscle or show where fat is stored. - Waist-to-height ratio adds information about fat around the middle, which is more closely linked with diabetes and heart disease. - A simple rule of thumb: keep your waist to less than half your height. A ratio of 0.5 or more signals increased health risk. - New diagnostic criteria ask doctors to confirm excess body fat with a second measure, such as the waist, rather than relying on BMI alone.

You have probably calculated your BMI at some point, perhaps on a form at the doctor's or in an app. It gives you a single number and a label. What it does not tell you is whether that number reflects muscle or fat, or where on your body any extra fat sits.

This guide explains what BMI does well, where it falls short, why doctors increasingly measure the waist too, and how to work out your own waist-to-height ratio at home. It also covers what the thresholds mean and what to do with the result.

What does BMI measure?

Body mass index is your weight in kilograms divided by your height in metres squared. If you weigh 80 kg and are 1.70 m tall, your BMI is 80 ÷ (1.70 × 1.70), which is about 27.7. You can work yours out with the BMI calculator.

The WHO uses these adult categories:

BMI (kg/m²)	Category
Under 18.5	Underweight
18.5 to 24.9	Healthy weight
25 to 29.9	Overweight
30 or more	Obesity

BMI is cheap, fast and needs no special equipment. Across large populations, higher BMI is clearly linked with higher rates of type 2 diabetes, high blood pressure, heart disease and several cancers. That is why it remains the starting point in most guidelines.

Where BMI falls short

BMI was designed to describe populations, not to diagnose individuals. Its main blind spots are:

• Muscle. Muscle is denser than fat. A person who does a lot of strength training can have a BMI in the overweight range with little body fat.
• Fat distribution. Two people with the same BMI can store fat very differently. Fat inside the abdomen, around the organs, carries more risk than fat on the hips and thighs. Our guide to abdominal fat explains why.
• Ethnicity. People of South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean backgrounds tend to develop weight-related conditions at lower BMIs. The NICE guideline on overweight and obesity therefore uses lower thresholds for these groups: overweight from 23 and obesity from 27.5.
• Age. Older adults tend to lose muscle and gain fat while their weight stays similar, so BMI can underestimate body fat. NICE advises interpreting BMI with caution in people aged 65 and over.
• Pregnancy and some health conditions. Fluid retention, pregnancy and some illnesses make BMI unreliable.

None of this means BMI is useless. It means it works best as one piece of information rather than the whole picture.

Why the waist adds so much

Waist size gives a rough idea of how much fat is stored around the middle. The consensus statement on waist circumference from an international working group argued that the waist should be measured routinely, as a "vital sign" alongside BMI. Its reasoning: at any given BMI, a larger waist is linked with higher risk of illness and death, and waist size can improve with exercise even when weight barely changes.

Waist circumference on its own has a drawback, though. A 90 cm waist means something different for someone who is 1.55 m tall than for someone who is 1.90 m tall. That is where the ratio comes in.

Waist-to-height ratio

Waist-to-height ratio (WHtR) is your waist measurement divided by your height, both in the same units. A systematic review and meta-analysis of 31 studies, covering more than 300,000 adults in several ethnic groups, found that, across these outcomes, WHtR was better than both BMI and waist circumference at picking out adults with cardiometabolic risk factors such as high blood pressure, type 2 diabetes and cardiovascular disease. It worked in both men and women.

The appeal is its simplicity. The same message, "keep your waist to less than half your height", applies to adults of any sex and ethnic background. NICE now recommends that adults with a BMI under 35 have their waist-to-height ratio measured alongside their BMI.

How to measure your waist-to-height ratio at home

You need a flexible tape measure and a few minutes.

1. Stand up straight with your feet together and your stomach relaxed. Do not hold your breath in.
2. Find the bottom of your lowest rib and the top of your hip bone at the side. Place the tape around your bare waist halfway between the two.
3. Keep the tape level all the way round and snug, without pressing into the skin.
4. Breathe out normally and read the measurement at the end of the out-breath.
5. Measure your height without shoes, against a wall.
6. Divide your waist by your height. For example, an 84 cm waist and 168 cm height gives 84 ÷ 168 = 0.50.

Different guidelines describe slightly different tape positions. The working group behind the waist consensus noted that the main tape positions predict health risk in a similar way, so what matters most for tracking is using the same method each time.

What the numbers mean

The thresholds below are those used in the NICE guideline for waist-to-height ratio, alongside widely used European waist circumference cut-offs.

Measure	Lower risk	Increased risk	High risk
Waist-to-height ratio (all adults)	0.40 to 0.49	0.50 to 0.59	0.60 or more
Waist circumference, women	Under 80 cm	80 to 87 cm	88 cm or more
Waist circumference, men	Under 94 cm	94 to 101 cm	102 cm or more

A few things to keep in mind:

• These are screening thresholds, not diagnoses. They tell you whether a closer look is worth it.
• Waist circumference cut-offs may be lower for some ethnic groups, which is one reason the ratio is easier to use.
• Waist measures are not used to assess risk during pregnancy.

BMI and waist together: the new view of obesity

In 2025, a Lancet commission on clinical obesity proposed new diagnostic criteria. It recommended that BMI alone should not be used to diagnose obesity in an individual. Instead, excess body fat should be confirmed with at least one other measure, such as waist circumference, waist-to-hip ratio or waist-to-height ratio, or with a direct measurement of body fat. At very high BMIs, above 40, excess fat can reasonably be assumed.

The commission also separated two situations:

Term	What it means
Preclinical obesity	Excess body fat with normal organ function, but a higher risk of future illness
Clinical obesity	Excess body fat that is already affecting how organs work or limiting everyday activities

Signs of clinical obesity can include breathlessness, joint pain that limits movement, raised blood sugar or blood pressure linked to weight, and fatty liver. This framework is still being adopted, and not every health system uses it yet, but it reflects a broad shift: doctors want to know how weight is affecting your health, not only how much you weigh.

What to do with your result

If your waist-to-height ratio is 0.5 or above, it is a prompt rather than a verdict. Useful next steps:

• Get a fuller picture. A doctor can check blood pressure, blood sugar, cholesterol and liver health, which tell you far more than any tape measure. Fat in the liver is common when the waist is large; see our guide to fatty liver and weight loss.
• Aim for small changes first. Even a modest reduction in waist size is linked with lower risk. Our article on realistic weight-loss goals explains why a 5 to 10% loss matters.
• Track trends. Measure every two to four weeks, at the same time of day, rather than daily.
• Move more. Regular activity reduces fat around the middle, sometimes before the scale shows much change.

How Docalo can help

Docalo is an online medical service focused only on weight loss. Your €49/month membership covers a doctor consultation, a personal plan and follow-up with the medical team, looking at measures like your waist and overall health, not just your BMI.

A licensed doctor reviews your health questionnaire and decides whether treatment is appropriate for you. If they prescribe medication, it is paid separately at the pharmacy. If your numbers have raised questions, you can start your consultation and talk them through with a doctor.