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Health & Fitness · Body Metrics Formula verified

BMI Calculator

Work out your Body Mass Index in metric or US units, see your weight category, and find the healthy weight range for your height.

Units
cm
100160220
kg
30105180
On-screen number pad
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Body Mass Index
22.9
Healthy weight
Healthy weight range for your height
56.7 – 76.3 kg

Step-by-step proofCheck by hand
BMI is a screening tool, not a diagnosis. It does not distinguish muscle from fat and can misclassify very muscular or very lean people, older adults, and some other groups. It is not appropriate for children or during pregnancy. Consult a qualified healthcare provider for an assessment of your individual health.
Visual breakdown

Where your BMI falls

The scale runs from underweight through healthy weight, overweight and obese, using the WHO/CDC adult thresholds. The marker shows your BMI's position on that scale.

How BMI is calculated

Body Mass Index is weight divided by height squared. In metric units that's kilograms divided by meters squared; the US form multiplies pounds divided by inches squared by 703, a rounded constant that folds the unit conversion into the same formula — both routes describe the same underlying number, they just start from different units.

BMI is a screening tool developed from population data, not a diagnosis. It uses only weight and height, so it cannot distinguish muscle from fat — a very muscular person can register a "high" BMI while carrying very little body fat.

The categories, in full
Under 18.5: underweight. 18.5–24.9: healthy weight. 25–29.9: overweight. 30 and above: obese. These are the WHO/CDC adult thresholds and are not used the same way for children, teens or pregnant women.
Not a diagnosis on its own
Health organizations increasingly recommend reading BMI alongside other measures — waist circumference, body composition, or a clinical assessment — rather than in isolation.

The formula

BMI = weight (kg) ÷ height (m)²

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

Worked example

A person weighing 70 kg at 175 cm (1.75 m) tall: BMI = 70 ÷ 1.75² = 70 ÷ 3.0625 = 22.9 — inside the 18.5–24.9 healthy weight range. The healthy weight range for someone 175 cm tall is 56.7 kg to 76.3 kg.

Frequently asked questions

What is BMI and how is it calculated?
Body Mass Index is weight divided by height squared — in metric units, kilograms ÷ meters². It's a quick screening number that correlates with body fat at a population level, not a direct measurement of body fat itself. The US version multiplies pounds ÷ inches² by 703, a rounded conversion constant that folds the unit conversion into the same formula.
Why doesn't BMI account for muscle mass?
Because it only uses weight and height — it has no way to distinguish a kilogram of muscle from a kilogram of fat. This is BMI's best-known limitation: a very muscular person can have a "high" BMI while carrying very little body fat, and a sedentary person with a "normal" BMI can still carry excess fat. BMI is a population-level screening tool, not an individual diagnosis.
What are the BMI weight categories?
The WHO/CDC adult categories are: under 18.5 is underweight, 18.5 to 24.9 is healthy weight, 25 to 29.9 is overweight, and 30 or above is obese. These thresholds were developed from adult population data and are not applied the same way to children, teenagers, or pregnant women, who use different growth-chart-based standards.
Is BMI accurate for everyone?
No. Beyond the muscle-versus-fat limitation, BMI tends to run differently across age groups, sexes, and some ethnic populations at the same underlying body-fat percentage, and several major health bodies now recommend interpreting it alongside other measures — waist circumference, body composition, or a clinical assessment — rather than on its own.
Sources and method
  • BMI formula and adult weight categories — Centers for Disease Control and Prevention (CDC), Body Mass Index reference. Also published by the World Health Organization (WHO).
  • 703 conversion constant for the pounds/inches form — CDC, "About Adult BMI."
Last reviewed: 19 Sep 2026 Sources last verified: 19 Sep 2026 Results use the assumptions explained on this page. Report an error How we check calculations

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