BMI calculator (body mass index for adults)

Enter your values. The answer and the full worked solution update as you type.

Result

BMI22.86 kg/m²
Category (WHO, adults)normal weight
Healthy weight range for this height (BMI 18.5–24.9)56.66 – 76.26 kg

For adults only: children and teenagers are assessed with BMI-for-age percentiles. BMI does not distinguish muscle from fat. For exam practice only. This is a study aid, never a clinical decision: always follow the prescription, local protocols and the product information.

Calculate the body mass index (BMI) of an adult from height and weight, in metric units or in inches and pounds. The calculator gives the BMI, the World Health Organization category and the weight range that corresponds to a BMI of 18.5 to 24.9 at that height, with every step shown.

Step-by-step solution

Body mass index = weight ÷ height²

BMI = 70 kg / (1.75 m)² = 22.86 kg/m²

Category (WHO, adults)

below 18.5 underweight; 18.5–24.9 normal weight; 25–29.9 overweight; 30–34.9 obesity class I; 35–39.9 obesity class II; 40 or more obesity class III
BMI 22.86 → normal weight

Healthy weight range

18.5 × 1.75² = 56.66 kg
24.9 × 1.75² = 76.26 kg

Key formulas

Body mass index
BMI = kg/m²

How to calculate BMI

  1. Convert the height to metres (cm ÷ 100, or in × 0.0254) and the weight to kg (lb × 0.4536).
  2. Square the height: 1.75 m × 1.75 m = 3.0625 m².
  3. Divide the weight by the squared height: 70 kg ÷ 3.0625 m² = 22.9 kg/m².
  4. With inches and pounds you can also use BMI = 703 × lb ÷ in².
  5. Read the WHO category: below 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30 or more obesity (classes I, II and III from 30, 35 and 40).

Questions and answers

Where do the BMI categories come from?

From the World Health Organization (WHO Technical Report Series 894, “Obesity: preventing and managing the global epidemic”, 2000). Some countries use lower cut-offs for people of Asian origin.

Can I use BMI for children?

No. For children and teenagers BMI is compared with BMI-for-age growth charts and percentiles, because body composition changes as they grow.

What are the limits of BMI?

BMI does not separate muscle from fat or show where fat is stored. A muscular athlete can have a high BMI without excess fat, and an older adult a normal BMI with little muscle.

Why is 703 used with pounds and inches?

Converting lb to kg and inches to metres gives the factor 0.45359237 ÷ 0.0254² = 703.07, usually rounded to 703.

Practise it yourself

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