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Ideal Weight Calculator
Healthy weight range using Robinson, Miller and Hamwi formulas.
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BMI Calculator
Body Mass Index with WHO classification and healthy weight range. No signup — your inputs stay in your browser.
Step By Step
How to Use This Calculator
4 steps
- Choose your preferred units — kg/cm or lbs/ft+in.
- Enter your body weight in the Weight field.
- Enter your height (in centimetres, or feet and inches).
- Your BMI and WHO category appear instantly below the inputs.
Worked Example
Example: 70 kg, 175 cm adult
Use this sample to sanity-check your inputs and understand what the final result represents.
- 1Weight: 70 kg
- 2Height: 175 cm (5 ft 9 in)
- 3BMI = 70 ÷ (1.75 × 1.75)
Final Result
BMI = 22.9 → Normal weight (WHO range 18.5 – 24.9)
Methodology
BMI Formula (WHO / CDC standard)
This section explains the calculation logic, assumptions, and source material used to make the result more trustworthy and easier to verify.
Metric: BMI = weight (kg) ÷ height (m)². Imperial: BMI = 703 × weight (lb) ÷ height (in)². Source: World Health Organization (WHO) obesity classification; Quetelet A. (1832) — the ratio was named 'Body Mass Index' by Keys et al. (1972, Journal of Chronic Diseases). WHO normal range 18.5–24.9 is based on population risk studies for adults aged 18+. BMI does not distinguish muscle from fat and is a screening tool, not a diagnostic measure.
Frequently Asked Questions
What is BMI and who developed it?+
Body Mass Index (BMI) is a simple ratio of weight to height squared. It was first described by Belgian mathematician Adolphe Quetelet around 1832 and later named 'Body Mass Index' by Ancel Keys et al. in a 1972 study published in the Journal of Chronic Diseases. The World Health Organization (WHO) adopted it as a standard adult obesity screening tool in its 1995 and 2000 reports.
What is the BMI formula?+
Metric: BMI = weight (kg) ÷ height (m)². Example: 70 kg and 1.75 m → 70 ÷ (1.75²) = 22.9. Imperial: BMI = 703 × weight (lb) ÷ height (in)². This calculator converts your inputs to metric internally before computing.
What is a healthy BMI for adults?+
According to WHO guidelines, a BMI of 18.5–24.9 is considered normal weight for adults. Below 18.5 is underweight; 25–29.9 is overweight; 30 and above is obese (with sub-classes I, II, III). These cutoffs are based on population-level mortality and disease risk data and apply to adults aged 18 and over.
Is BMI accurate for everyone?+
BMI is a population-level screening tool, not an individual diagnostic measure. It does not distinguish fat mass from muscle mass, so highly muscular athletes may register as 'overweight' despite low body fat. It also does not account for fat distribution (visceral vs. subcutaneous), age-related muscle loss in older adults, or ethnic differences in risk thresholds (e.g., some Asian health guidelines use a lower cutoff of 23 for overweight). For a fuller picture, clinicians may use waist circumference, DEXA scans, or body fat percentage alongside BMI.
Does BMI apply to children and teenagers?+
No — this calculator is for adults aged 18 and over. For children and adolescents (2–19 years), the CDC and WHO use BMI-for-age percentile charts because body composition changes significantly during growth. A paediatrician should interpret BMI in children.
What should I do if my BMI is outside the normal range?+
Use your result as a starting point for a conversation with a qualified healthcare provider. A doctor can consider your full health picture — blood pressure, cholesterol, blood glucose, waist circumference, lifestyle, and family history — before making any recommendations. This tool is for general wellness awareness, not medical diagnosis.