Calculate your Body Mass Index with WHO classification, normal-weight range for your height and the corrected 'New BMI' (Oxford formula).
Fill in the fields below and click "Calculate".
Calculating BMI: Formula, WHO Chart and the Index's Limits
The Body Mass Index relates your weight to your height: BMI = weight in kg ÷ (height in m)². Example: at 1.80 m and 75 kg the result is 75 ÷ 3.24 = 23.1 – normal weight. The calculator also shows the weight range that keeps you in the normal band (BMI 18.5–24.9) for your height: at 1.80 m that is 59.9 to 80.7 kg.
The WHO classification
Below 18.5 counts as underweight, 18.5–24.9 as normal weight, 25–29.9 as overweight (pre-obesity). Obesity class I starts at 30, class II at 35, class III at 40. These thresholds apply to adults; children and teenagers require age-specific percentile curves, which this calculator does not cover.
Why the 'New BMI' is often fairer
The classic formula penalises tall people and flatters short ones: it scales weight with the square of height although bodies grow in three dimensions. Mathematician Nick Trefethen (University of Oxford) therefore proposed 1.3 × weight ÷ height^2.5. At 1.80 m/75 kg the value drops from 23.1 to 22.4 – for very tall or short people the difference can amount to half a category.
What BMI cannot tell you
BMI does not distinguish between muscle and fat mass: a muscular athlete quickly lands in the 'overweight' band despite low body fat. Fat distribution (abdominal fat is riskier than hip fat) also remains invisible – waist circumference or the waist-to-height ratio are better markers for that. For people aged 65 and over, a slightly higher range of about 24–29 is considered favourable because reserves are protective in old age. Pregnant women should not use BMI at all. In short: BMI is a quick screening tool, not a diagnosis.
