Tulnest

BMI Calculator

Calculate your Body Mass Index in metric (cm/kg) or imperial (ft/in/lb) units. See your BMI category and the healthy weight range for your height.

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kg

Body Mass Index (BMI) is a simple ratio of weight to height squared. It's a quick screening tool — not a definitive diagnosis — used to flag whether your weight is in a range associated with reduced health risk for most adults.

Toggle between metric and imperial units. The healthy weight range below the result is what corresponds to a BMI of 18.5 – 24.9 at your specific height, so it's a more actionable target than the abstract BMI number alone.

BMI has known limitations. It doesn't distinguish muscle from fat, doesn't apply well to athletes or older adults, and isn't designed for children. If your number sits near a category boundary, talk to a doctor before changing anything based on it.

How to use

  1. Pick metric or imperial units depending on what you have to hand.
  2. Enter your height and weight.
  3. Read your BMI value, the category band (Underweight, Normal, Overweight, Obese), and the corresponding healthy-weight range for your height.

Frequently asked questions

What's the formula for BMI?
Metric: BMI = weight (kg) / height (m)². Imperial: BMI = 703 × weight (lb) / height (in)². Both formulas give the same number for the same body.
Is BMI an accurate health measure?
BMI is a screening tool, not a diagnosis. It doesn't distinguish muscle from fat, so very muscular people often score "Overweight" while still being healthy. It's also less reliable for older adults, athletes, pregnant people and very tall or short individuals. Treat it as one data point.
What are the BMI categories?
Per the NIH for adults: Underweight < 18.5; Normal 18.5–24.9; Overweight 25.0–29.9; Obese ≥ 30.0. Different categories apply for children and teens; consult a doctor or use age- and sex-specific charts.

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