BMI Calculator

Calculate BMI

cm
kg

BMI

24.2

Category

Normal weight

See how this is calculated

How This Calculation Works

Body Mass Index (BMI) is calculated by dividing your weight in kilograms by the square of your height in meters: BMI = weight (kg) ÷ height (m)². It's a simple screening tool developed in the 19th century that estimates whether your weight falls within a range typically associated with good health for your height.

The result is compared against four standard World Health Organization categories: under 18.5 is classified as underweight, 18.5–24.9 as normal weight, 25–29.9 as overweight, and 30 and above as obese. These thresholds are the same for adult men and women, though some regional guidelines adjust them slightly for different populations.

BMI is popular because it's fast, free, and requires no special equipment — just a height and a weight. But it was never designed to be a precise diagnostic tool for any individual; it's a population-level screening measure, which is why it has well-known limitations discussed below.

Common Mistakes to Avoid

  • Treating BMI as a direct measure of body fat. BMI cannot distinguish between muscle and fat. A muscular athlete can have a "high" BMI despite very low body fat, while someone with little muscle mass can have a "normal" BMI despite high body fat.
  • Ignoring body composition entirely. Two people with an identical BMI can have very different health profiles depending on where fat is distributed and how much muscle they carry. Consider pairing BMI with a body fat percentage estimate for a fuller picture.
  • Applying adult categories to children or teens. BMI for people under 20 should be interpreted using age- and sex-specific percentile charts, not the flat adult categories used here.
  • Using BMI alone to make medical decisions. BMI is a screening tool, not a diagnosis. Blood pressure, cholesterol, blood sugar, and other markers matter — talk to a healthcare provider for a complete assessment.

Worked Example

Scenario: A person who is 170 cm tall and weighs 70 kg.

Step 1 — Convert height to meters: 170 cm = 1.70 m.

Step 2 — Square the height: 1.70 × 1.70 = 2.89 m².

Step 3 — Divide weight by height squared: 70 ÷ 2.89 ≈ 24.2.

Result: A BMI of 24.2 falls in the "Normal weight" category (18.5–24.9).

Frequently Asked Questions

What is considered a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is classified as the normal or healthy weight range by the World Health Organization. However, this range doesn't account for muscle mass, bone density, age, or sex, so it should be treated as a general guideline rather than an absolute target.
Is BMI accurate for athletes or very muscular people?
No — BMI often overestimates body fat in muscular individuals because muscle is denser than fat. A bodybuilder or strength athlete can have a BMI in the "overweight" or "obese" range while having a low, healthy body fat percentage. Body fat percentage or waist circumference are better indicators for these populations.
Does BMI differ for men and women?
The BMI formula and standard categories are the same for adult men and women. However, women naturally tend to carry a higher percentage of body fat than men at the same BMI, which is one reason BMI alone doesn't capture the full picture of body composition.
Should I use BMI to track my weight loss progress?
BMI can be one data point, but weight, waist circumference, body fat percentage, and how your clothes fit are often more meaningful for tracking body composition changes over time — especially if you're gaining muscle while losing fat, in which case BMI may barely change even as your body composition improves.

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