BMI Calculator

Body Mass Index (BMI) is a simple ratio of weight to height used as a screening indicator of weight-related health risk. It works for most adults and takes seconds to calculate. Doctors read the number alongside age, sex and muscle mass, because the score alone never tells the whole story.

Enter values

Results

Your BMI: 22.5
Category: Normal weight
Healthy weight for your height: 53.5 – 72 kg

How is the BMI calculated?

Enter your height and weight — metric (cm/kg) or imperial (inches/pounds). The calculator divides your weight by the square of your height and places the result in the standard adult categories. The category — underweight, normal weight, overweight or obese — appears beside the score using the WHO adult cut-offs.

Formula

BMI = weight (kg) ÷ height (m)²

Imperial: BMI = weight (lb) ÷ height (in)² × 703

Categories (adults):
Below 18.5 — Underweight
18.5 – 24.9 — Normal weight
25.0 – 29.9 — Overweight
30.0 and above — Obese

Example

Height: 170 cm · Weight: 65 kg
BMI = 65 ÷ (1.70)² = 65 ÷ 2.89 ≈ 22.5
Result: normal weight range (18.5 – 24.9)

Imperial check: 143 lb ÷ (67 in)² × 703 ≈ 22.4 — the same score from pounds and inches. A 5 kg difference at this height moves the score by about 1.7 points, which is why steady weighing matters more than one dramatic reading.

Things to remember

BMI is a screening tool, not a diagnosis. It does not distinguish muscle from fat, so athletes and older adults should read it alongside other measurements such as waist circumference.

Frequently Asked Questions

What is BMI and what does it measure?

BMI, or Body Mass Index, is a number calculated from your weight and height that serves as a rough indicator of body fat and weight-related health risk for adults.

What is considered a healthy BMI range?

For most adults a BMI between 18.5 and 24.9 is considered normal weight. 25 to 29.9 is overweight and 30 or above is obese, while below 18.5 is underweight.

Does BMI apply to children and teenagers?

Not directly. Children's BMI is interpreted using age- and sex-specific percentiles rather than the adult cutoffs, so a paediatrician or growth chart should be used for anyone under 20.