BMI Calculator

Enter your height and weight to check your Body Mass Index and healthy weight range.

What is BMI?

Body Mass Index (BMI) is a simple screening measure that relates your weight to your height. Devised in the 1830s by Belgian statistician Adolphe Quetelet — which is why it was long called the Quetelet Index — it became the world's standard weight-status indicator because it needs only two numbers anyone can measure at home. It is calculated as weight in kilograms divided by height in metres squared (kg/m²). It gives doctors and public-health bodies a fast, cheap way to flag people who may be at higher risk from low or high body weight, without any lab test or equipment.

The BMI formula, with a worked example

The formula is BMI = weight (kg) ÷ height (m)². Say you weigh 70 kg and are 170 cm (1.70 m) tall. First square the height: 1.70 × 1.70 = 2.89. Then divide: 70 ÷ 2.89 = 24.2 — a healthy-range BMI. If you work in pounds and inches instead, the imperial version is BMI = 703 × weight (lb) ÷ height (in)². For 154 lb at 67 in: 703 × 154 ÷ (67 × 67) = 108,262 ÷ 4,489 = 24.1 — the same result, as it should be. The calculator above does either automatically; you never have to square anything by hand.

How to calculate BMI in kg and cm

Most of the world measures height in centimetres and weight in kilograms, so this is the version people need most often. There is one small catch: the formula needs height in metres, not centimetres. Divide your height in cm by 100 first, then apply BMI = kg ÷ m².

Worked example in kg and cm — someone who is 165 cm and 62 kg:

1. Convert the height: 165 cm ÷ 100 = 1.65 m
2. Square it: 1.65 × 1.65 = 2.7225
3. Divide the weight: 62 ÷ 2.7225 = 22.8

A BMI of 22.8 sits comfortably in the healthy range. Forgetting step 1 and dividing by 165² is the single most common mistake — it produces a meaningless number like 0.0023. The calculator above takes centimetres and kilograms directly and handles the conversion for you, so you can simply type 165 and 62 and read the answer.

Here are some quick reference results in kg and cm:

BMI categories and what they mean for health

The World Health Organization uses these categories for adults, with broadly rising health risk as you move away from the healthy band:

• Below 16.0 — severe thinness
• 16.0 – 18.4 — underweight; can signal undernutrition, and is linked to weaker immunity, bone loss and fertility issues
• 18.5 – 24.9 — healthy weight; the range associated with the lowest risk for most adults
• 25.0 – 29.9 — overweight; a warning zone where risk of type 2 diabetes and heart disease begins to climb
• 30.0 – 34.9 — obesity class I
• 35.0 – 39.9 — obesity class II
• 40.0 and above — obesity class III (severe)

Higher BMI is associated with greater risk of high blood pressure, type 2 diabetes, heart disease, stroke, gallstones, several cancers and joint problems. Being underweight carries its own risks. Remember these are associations across large populations, not a verdict on any one person — plenty of healthy people sit just outside the "healthy" band.

Why South Asians should use lower cut-offs

This matters a lot for visitors in Pakistan, India, Bangladesh and across South and East Asia. Research shows people of South Asian and East Asian descent tend to carry more body fat — especially around the abdomen and organs — at the same BMI as people of European descent, and develop diabetes and heart disease at lower BMI values. Because of this, the WHO and many Asian health authorities recommend lower thresholds: overweight from a BMI of 23, and obesity from 27.5, rather than 25 and 30. If your BMI is between 23 and 25, the standard chart may call you "healthy" while an Asia-specific chart flags you as needing attention — worth discussing with your doctor.

BMI vs. waist size and body composition

BMI's biggest blind spot is that it can't tell muscle from fat or show where fat sits. A simple companion measure is waist circumference: fat around the belly (visceral fat) is more dangerous than fat on the hips and thighs. As a rough guide, health risk rises with a waist above about 90 cm (35 in) for South Asian men and 80 cm (31.5 in) for South Asian women — lower than the ~102 cm / 88 cm figures used for European populations. The waist-to-height ratio is even simpler: keep your waist under half your height. Used alongside BMI, these give a much clearer picture than BMI alone.

When BMI is misleading

BMI is a screening tool, not a diagnosis, and it is less reliable for several groups:

• Athletes and muscular people — heavy muscle pushes BMI into "overweight" despite low body fat.
• Older adults — muscle is lost with age, so a "normal" BMI can hide excess fat.
• Children and teens — they use age-and-sex percentile charts, not the adult categories.
• Pregnant women — BMI is not meaningful during pregnancy; use pre-pregnancy weight with medical guidance.
• Very tall or very short people — the height-squared formula slightly over- or under-estimates at the extremes.

If your BMI is borderline, don't panic or over-react to a single number. Blood pressure, blood sugar, cholesterol, waist size and fitness level together tell you far more than BMI on its own.

How to move toward a healthier BMI

If you want to shift your BMI, slow and steady beats crash dieting. A safe target is about 0.5 kg (1 lb) per week, which comes from a modest daily deficit of roughly 500 calories — you can estimate your daily needs with our Calorie Calculator. Build meals around vegetables, whole grains, beans and lean protein; move your body most days, mixing walking or cycling with some strength work to protect muscle; prioritise sleep, since poor sleep drives weight gain; and drink water instead of sugary drinks. Even a 5–10% change in weight can meaningfully improve blood pressure and blood sugar. Before starting any major weight-change programme, check in with a doctor or dietitian.

Frequently asked questions