What this calculator does
It calculates body mass index from height and weight, places the result in the WHO adult bands, and shows the weight range that would put you between 18.5 and 24.9 for your height.
BMI is a population screening tool. It is useful because it is quick and consistent; it is limited because it cannot tell muscle from fat, or fat around organs from fat under the skin.
The formula
BMI = weight (kg) ÷ height (m)²At 75 kg and 1.70 m: 75 ÷ (1.70 × 1.70) = 75 ÷ 2.89 = 26.0.
A worked example
- Height: 170 cm
- Weight: 75 kg
- BMI: 26.0 — overweight (25–29.9)
- Healthy weight range for 170 cm: 53.5–72.0 kg
At 70 kg the same height gives 24.2, inside the healthy range.
What BMI misses
- Muscle. A rugby player and a sedentary person can share a BMI with very different body composition.
- Fat distribution. Waist circumference adds information that BMI does not.
- Age and ethnicity. Risk thresholds differ for some populations; some guidance uses lower cut-offs for Asian populations.
- Pregnancy and children. Different rules apply; this page does not cover them.
What this calculator does not do
It does not diagnose obesity, estimate body fat, or replace a clinical assessment. A number outside the healthy band is a prompt to look at the whole picture, not a diagnosis. If you are concerned, speak to a clinician.
BMI and waist circumference
BMI does not show where fat sits. Waist circumference adds that: risk rises with abdominal fat even at the same BMI. For adults, many guidelines use 94 cm for men and 80 cm for women as a first threshold, with different thresholds for some populations. Measure at the navel, at the end of a normal breath. It is a second screening number, not a diagnosis.
Frequently asked questions
What is BMI?
Body mass index is weight in kilograms divided by height in metres squared. It is a screening number, not a measure of body fat, fitness or health on its own.
What are the WHO bands?
Under 18.5 is underweight, 18.5–24.9 is the healthy range, 25–29.9 is overweight, 30–34.9 is obesity class I, 35–39.9 is class II and 40 or more is class III. The bands are for adults.
Why is BMI wrong for athletes?
Muscle is denser than fat, so a muscular person can have a high BMI with low body fat. BMI also says little about where fat sits. Waist circumference or a body-fat estimate is more informative in that case.
Does BMI apply during pregnancy or to children?
No. Pregnancy changes weight and blood volume, and children need age-and-sex-specific percentiles. This calculator is for non-pregnant adults.