BMI Calculator for Men, Women & Children

BMI Categories — WHO Reference Table for Adults

The table below shows the official weight classifications set by the World Health Organization for adults aged 18 and over. These thresholds are the global standard used by doctors, dietitians, and public health researchers when assessing weight-related health risk.

BMI Percentile Categories for Children (CDC Reference)

For children and teenagers between 2 and 17 years old, the BMI formula is identical to the adult version. However, the result is interpreted entirely differently. Rather than fixed cutoff numbers, the CDC uses percentile charts that account for the child's age and sex, because what constitutes a healthy body composition shifts naturally as children grow and develop.

Understanding BMI: What It Is, How It Works, and Why It Matters

Body Mass Index — commonly known as BMI — is one of the most widely used health screening tools in the world. It gives you a single number that relates your weight to your height, providing a quick sense of whether your weight falls within a range associated with good health. It is a starting point rather than a final verdict, and understanding what it actually tells you makes a real difference in how you interpret the result.

The formula is straightforward. In metric units, you divide your weight in kilograms by your height in metres squared. So if you weigh 72 kg and stand 1.75 m tall, your BMI is 72 ÷ (1.75 × 1.75), which works out to approximately 23.5 — solidly in the healthy range. In imperial units, the calculation uses a conversion factor: weight in pounds × 703, divided by height in inches squared. Both produce the same result.

This calculator supports both metric and imperial inputs. It also lets you select your profile — male, female, or child — because the context around your BMI changes meaningfully depending on who you are. The number is calculated the same way, but what it means for your body varies considerably.

BMI for Men: What the Numbers Mean for the Male Body

Men and women have genuinely different body compositions, even at identical heights and weights. On average, adult men carry about 6 to 11 percentage points less body fat than women of the same BMI. This means a man with a BMI of 25 typically has a lower proportion of body fat than a woman at the same figure.

For most adult men, the standard WHO thresholds apply: a BMI between 18.5 and 24.9 is healthy, 25 to 29.9 is overweight, and 30 or above falls into the obese range. Where this gets nuanced is with muscular men. A highly trained athlete with substantial muscle mass can push a BMI above 25 or even 30, yet their body fat percentage may be perfectly healthy. This is BMI's most well-known limitation, and it is why the number should always be considered alongside other measures for active individuals.

Men are also statistically more prone to carrying excess weight around the abdomen, which carries higher cardiovascular risk than fat distributed elsewhere. A waist circumference above 94 cm (37 inches) is a risk indicator for men regardless of BMI. Pairing your result with a simple tape measure gives you a considerably more complete picture of your metabolic health.

BMI for Women: Hormones, Body Composition, and Healthy Ranges

For women, the standard BMI scale applies — but the physiology behind it is different enough that context really matters. Women naturally carry more essential body fat than men, primarily due to hormonal differences and the physiological demands associated with reproduction. At the same BMI, a woman's body fat percentage will typically be higher than a man's, and this is entirely normal.

Pregnancy is one situation where BMI becomes temporarily irrelevant. Natural weight gain during pregnancy is healthy and necessary, and evaluating BMI at this time does not provide meaningful information. After menopause, women often experience shifts in where the body stores fat — moving more toward the abdominal area — which can alter health risk profiles even without a visible change in BMI.

Research also suggests that some women of South Asian and East Asian heritage may face elevated health risks at BMI levels below the standard overweight threshold, due to differences in fat distribution patterns. Some clinicians apply an adjusted cutoff of 23 for these populations — a point worth raising with your GP alongside any BMI result.

BMI for Children: Why It's Interpreted Differently

Calculating BMI for a child uses exactly the same mathematical formula as for adults. What changes entirely is how you read the result. A BMI of 20 means something very different for an 8-year-old than it does for a 35-year-old adult. Children's bodies are constantly changing, which means fixed adult thresholds like 25 or 30 simply do not apply.

Instead, children's BMI is interpreted using CDC growth charts, which place the result on a percentile scale relative to other children of the same age and sex. A child at the 85th percentile or above is considered overweight; at the 95th or above, obese — terms that describe where they fall relative to their peers, not a medical diagnosis on their own.

This percentile approach reflects the fact that healthy body fat genuinely varies with age. Toddlers naturally carry more fat than older children. Adolescent girls gain fat as a normal part of puberty, while adolescent boys typically gain muscle. A single reading should never be treated as a verdict — it is one data point that a paediatrician will consider alongside growth trends over time, activity levels, and family history.

What a Normal BMI Tells You — and What It Doesn't

A BMI in the healthy range of 18.5 to 24.9 is associated with the lowest statistical risk of weight-related conditions including type 2 diabetes, cardiovascular disease, joint problems, and certain cancers. This is why health organisations worldwide continue to use it as a population-level screening tool — it is imperfect, but it is quick, free, and reasonably predictive across large populations.

That said, BMI tells you nothing about where fat is distributed in your body, how much muscle you carry, your blood glucose or cholesterol levels, your cardiovascular fitness, or the quality of your diet. Think of your result as a flag, not a finding. If it lands in a range that warrants attention, treat it as a prompt to have a broader conversation with your doctor — not a cause for alarm on its own.