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BMI Calculator

Body Mass Index — metric and imperial

cm
kg
Your BMI
—
Enter your height and weight
<18.5 Under 18.5–24.9 Normal 25–29.9 Over ≥30 Obese

Free BMI calculator — metric & imperial, instant result

Toololis BMI Calculator computes Body Mass Index using the WHO standard formula. Enter height and weight in either metric (cm / kg) or imperial (ft·in / lb) — conversions happen automatically. Your BMI, category, and healthy weight range appear live.

BMI formula

  • Metric: BMI = weight(kg) ÷ height(m)²
  • Imperial: BMI = (weight(lb) ÷ height(in)²) × 703

BMI categories (WHO, adult)

  • Underweight: < 18.5
  • Normal: 18.5 – 24.9
  • Overweight: 25 – 29.9
  • Obese Class I: 30 – 34.9
  • Obese Class II: 35 – 39.9
  • Obese Class III: ≥ 40

How to use this tool

  1. 1

    Pick your unit system

    Toggle between Metric (cm/kg) and Imperial (ft/in/lb). Numbers update automatically when you switch.

  2. 2

    Enter height and weight

    Type your height and weight. The BMI is computed live — no need to click a button.

  3. 3

    Read the result

    Your BMI appears with a category label (Underweight, Normal, Overweight, Obese). The gauge shows where you sit on the standard WHO scale.

BMI limitations

  • Muscle mass — High-muscle individuals often exceed "Normal" despite low body fat
  • Age — Older adults lose muscle and bone; same BMI can mean different compositions
  • Body shape — BMI doesn\'t show fat distribution (belly fat is higher risk than hip fat)
  • Ethnicity — Asian populations face health risks at lower BMI thresholds
  • Pregnancy — BMI is not valid during pregnancy

For a more complete picture, pair BMI with waist circumference, body fat percentage, and resting heart rate / fitness level. For health decisions, always consult a qualified healthcare professional.

Frequently Asked Questions

What is BMI?
Body Mass Index — your weight divided by your height squared. Formula: BMI = weight(kg) / height(m)². It's a rough screening tool for weight status at the population level.
What are the BMI categories?
WHO standard: Underweight < 18.5, Normal 18.5–24.9, Overweight 25–29.9, Obese ≥ 30. Obese is further split into Class I (30–34.9), Class II (35–39.9), and Class III (≥ 40).
Is BMI accurate for athletes?
Often not. BMI does not distinguish muscle from fat. A muscular athlete can have a BMI of 27 (Overweight by the chart) while having 10% body fat — physically healthier than most "Normal BMI" individuals. Use waist-to-height ratio or body fat % for athletes.
Is BMI valid for children?
Children and teens use a different BMI calculation that accounts for age and sex (BMI-for-age percentiles). This calculator is for adults 20+ only.
Does BMI differ by ethnicity?
Yes. Research shows people of Asian descent develop health risks at lower BMI thresholds — WHO suggests a cutoff of 23 (rather than 25) for Overweight in Asian populations. This calculator uses standard thresholds; adjust interpretation accordingly.
Should I change my weight based on BMI?
BMI is a starting conversation, not a verdict. Combined with waist circumference, body composition, family history, and fitness level, it becomes useful. For health decisions, consult a clinician rather than acting on BMI alone.
What is ideal weight for my height?
The "healthy range" for your height is any weight that gives a BMI between 18.5 and 24.9. For a 170 cm adult, that's 53.5–72 kg. The calculator shows your healthy range based on your input.

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