Free BMI and ideal weight calculator
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BMI, healthy weight and ideal weight
There is no single ideal weight that applies to everyone. The calculator first shows a weight range associated with a BMI of 18.5 to 24.9 in adults. A range is more honest than one number because muscle mass, body shape, age, health and lifestyle all affect what weight means.
The healthy weight range is calculated from your height: the lower value is 18.5 × height² and the upper value is 24.9 × height², with height in metres. Two people of the same height can sit at different points in this range and both have healthy profiles.
Adult BMI thresholds are the same for women and men. Historical Lorentz, Devine and Robinson formulas use different coefficients according to sex, but they do not account for individual body composition and should remain comparison points.
Lorentz is an older estimate based on height and sex. Devine was proposed for medication dosing, while Robinson later derived another equation from height-weight tables. Their origins and coefficients differ, so their results do not always agree. Modern research suggests that a BMI-compatible range is generally more useful than one ideal value.
Body Mass Index (BMI) is a simple indicator used to assess a person's body composition. It's calculated by dividing weight (in kilograms) by the square of height (in meters). BMI is used as a screening tool to identify potential weight problems in adults.
BMI = Weight (kg) / Height² (m²)
For example, for a person weighing 70 kg and measuring 1.75 m:
BMI = 70 / (1.75 × 1.75) = 22.9
The World Health Organization (WHO) defines the following categories:
| IMC | BMI Categories (WHO) |
|---|---|
| < 18.5 | Underweight |
| 18.5 - 24.9 | Normal Weight |
| 25 - 29.9 | Overweight |
| 30 - 34.9 | Obesity Class I |
| 35 - 39.9 | Obesity Class II |
| ≥ 40 | Obesity Class III |
BMI is a useful indicator but doesn't account for several important factors:
Factors to consider:
- Body composition (muscle vs fat)
- Fat distribution
- Age and gender
- Physical activity level
- Ethnicity
Two people can have the same BMI but very different body compositions.
BMI has several important limitations:
Not suitable for:
- Athletes and highly muscular individuals
- Pregnant or breastfeeding women
- Elderly people
- Children and adolescents (use growth charts)
Alternatives to consider:
- Waist circumference
- Waist-to-hip ratio
- Body fat percentage
- Complete body composition
BMI is a screening tool, not a diagnostic tool.
Medical Disclaimer. This BMI calculator is provided for informational purposes only and does not replace the advice of a healthcare professional. If you have concerns about your weight or health, consult a qualified doctor or nutritionist.
Sources: WHO — adult BMI classification · PubMed — analysis of ideal weight formulas
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