Health & Fitness
BMI Calculator
Estimate adult Body Mass Index (BMI), see the category range, and calculate the weight associated with a target BMI. BMI is a screening tool, not a diagnosis.
BMI
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- Category
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- Healthy weight range
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- Range guidance
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Student quick launch
Grade planning, algebra checks, and formulas students reach for most.
Study path
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Follow these when you want the formula behind the answer, a short lesson, or nearby tools in the same topic.
What this BMI calculator can solve
| Mode | Use it when | Output |
|---|---|---|
| BMI from weight | You know height and weight | BMI, adult category, healthy range, and weight guidance |
| Weight for target BMI | You know height and target BMI | Target weight and change from current weight |
BMI formula
BMI compares weight with height. It is widely used as an adult screening tool, but it does not directly measure body fat or health.
Adult BMI categories
| Category | BMI range |
|---|---|
| Underweight | Less than 18.5 |
| Healthy weight | 18.5 to 24.9 |
| Overweight | 25.0 to 29.9 |
| Obesity class I | 30.0 to 34.9 |
| Obesity class II | 35.0 to 39.9 |
| Obesity class III | 40.0 or higher |
Worked examples
5 ft 7 in, 155 lb
Imperial adult BMI
BMI
24.3
170 cm, 70 kg
Metric adult BMI
BMI
24.2
Weight for BMI 22
Target BMI weight at 5 ft 7 in
BMI
22
Frequently asked questions
Is BMI accurate?+
BMI is useful as a broad screening tool, but it is not a diagnosis. It does not account for muscle, bone density, fat distribution, age, sex, pregnancy, or athletic training.
Is this for children?+
No. Children and teens use age- and sex-specific BMI percentiles, not the adult cutoffs shown here.
What is a healthy BMI?+
For adults, 18.5 to 24.9 is commonly categorized as healthy weight. Health depends on more than BMI, including labs, blood pressure, strength, sleep, and medical history.
Why calculate weight for a target BMI?+
It helps translate a BMI number into a weight at a given height. It should be used for context, not as a personal medical prescription.
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Last updated: May 8, 2026