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01What this calculator tells you

Body mass index (BMI) is a quick screen that compares your weight to your height. Enter your measurements and you get one number plus the weight category the World Health Organization assigns to it — underweight, normal, overweight, or obesity.

It also shows the healthy weight range for your height, so you can see how far a goal weight is from where you are now. To act on that number, our BMR calculator estimates the calories you burn at rest, while the protein intake and water intake calculators set sensible daily targets.

Works in both metric (kg, cm) and imperial (lb, ft/in).
Uses the standard adult WHO categories.
Shows your healthy weight range, not just a number.

02How to read your result

Find your number on the coloured scale. The categories below are the adult cut-offs used by the WHO and the U.S. Centers for Disease Control and Prevention.

Category
BMI
What it suggests
Underweight
Below 18.5
May signal under-nutrition; worth a check-up.
Normal
18.5 – 24.9
Associated with the lowest health risk for most adults.
Overweight
25 – 29.9
Slightly raised risk; small changes help.
Obesity
30 and above
Higher risk; a clinician can advise on next steps.
BMI is a starting point, not a diagnosis. Pair it with waist size and how you feel.
When BMI can mislead +×

Because BMI uses only height and weight, it cannot tell muscle from fat. A very muscular person may land in the “overweight” band while carrying little fat, and an older adult who has lost muscle may look “normal” while carrying more fat than is ideal.

  • Athletes and heavy-training individuals.
  • Older adults with reduced muscle mass.
  • Pregnant or breastfeeding people (BMI does not apply).
  • Children and teens, who use age-and-sex percentile charts instead.

Because BMI is only one signal, clinicians read it alongside waist circumference and other measures — the National Institute of Diabetes and Digestive and Kidney Diseases explains how these fit together.

03Related calculators

Working through a related project? Try our Body Shape Calculator, Carb Intake Calculator, and Starbucks Calorie Calculator.

01The BMI formula

BMI is weight divided by height squared. The metric version is the definition; the imperial version is the same maths with a unit conversion folded in.

Metric
BMI = weight(kg) / height(m)²
Imperial
BMI = 703 × weight(lb) / height(in)²

Where:

  • weight= your body weight in kilograms or pounds.
  • height= your standing height in metres or inches.

02Worked example

Take someone 175 cm tall weighing 70 kg:

  1. Convert height to metres: 175 ÷ 100 = 1.75 m.
  2. Square it: 1.75 × 1.75 = 3.0625.
  3. Divide weight by that: 70 ÷ 3.0625 = 22.9.

A BMI of 22.9 sits in the normal range. The same person in imperial (5 ft 9 in, 154 lb) gives 703 × 154 ÷ 69² ≈ 22.7 — the small gap is rounding.

03Common questions

Q What is a healthy BMI range?
For most adults the WHO defines a healthy BMI as 18.5 to 24.9.
Q How do I calculate BMI by hand?
Divide weight in kg by height in metres squared, or multiply pounds by 703 and divide by inches squared.
Q Is BMI accurate for athletes?
Often not — extra muscle raises weight and can push BMI into “overweight” without excess fat. The U.S. National Heart, Lung, and Blood Institute recommends pairing BMI with waist circumference.
This calculator is for general information and is not medical advice. Talk to a qualified healthcare professional about your individual health.

BMI Calculator

cm
kg
Enter your height and weight, then press Calculate.
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Body Mass Index
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1518.5253040
A healthy BMI for your height is 18.5–24.9, about --.
Elena Castillo ✓ Medically reviewed
Updated Jun 2026 · 5 min read · Reviewed by the InfoCalculator editorial team