Your BMI
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Marker position scales from BMI 10 to 45
Related Tools
About the BMI Calculator
Body Mass Index (BMI) is a screening measure that relates weight to height using the formula weight in kilograms divided by height in metres squared. Developed by Belgian statistician Adolphe Quetelet in the 1830s and popularised by physiologist Ancel Keys in 1972, it remains the global first-pass tool for classifying adult weight status because it needs nothing more than a scale and a tape measure.
This calculator computes your BMI in metric (cm, kg) or imperial (ft/in, lb) units, places it in the standard WHO adult category — underweight, normal, overweight, or three classes of obesity — and adds practical context: the healthy weight range for your height, your Body Surface Area via the Du Bois formula, and the Ponderal Index sometimes used for very tall or short adults.
A vital honesty note: BMI measures mass, not composition. Muscular athletes routinely register as overweight; older adults with reduced muscle can register normal while carrying excess fat. Treat BMI as a first indicator that something may be worth discussing with a professional — not as a diagnosis.
How to use the BMI Calculator
- 1 Choose Metric (centimetres and kilograms) or Imperial (feet/inches and pounds).
- 2 Enter your height and current weight in the revealed fields.
- 3 Read your BMI, WHO category, and the healthy weight band calculated for your height.
- 4 Check BSA and Ponderal Index for additional context, and track how the marker sits on the colour scale as values change.
Key features
Metric and imperial units
Switch systems instantly without converting anything yourself.
WHO category badge
Colour-coded classification against the standard adult cutoffs.
Healthy weight range
The minimum and maximum weights that keep your BMI between 18.5 and 24.9.
BSA and Ponderal Index
Du Bois body-surface area and the height-cubed alternative to BMI.
Visual scale marker
A marker on the category bar shows where your BMI sits between bands.
Who uses the BMI Calculator?
- Routine health check-ups and insurance medicals that record BMI.
- Weight-management journeys: setting an achievable target weight from the healthy range.
- Fitness coaching intake forms and progress tracking.
- Public-health and workplace wellness screening programmes.
- Students and researchers needing quick anthropometric calculations.
Tips and best practices
- Aim for the healthy band, not the lowest number: mortality curves flatten across 18.5–24.9, and being slightly above is far safer than crash dieting.
- Pair BMI with waist circumference (under 90 cm for Asian men, 80 cm for Asian women) to catch fat distribution that BMI misses.
- If you train with weights, consider body-fat percentage or waist-to-height ratio alongside BMI — muscle mass inflates the number.
- Recalculate after meaningful changes, not daily: weight fluctuates 1–2 kg with water, food, and salt.
- For children and teenagers, age-and-sex percentile charts apply — adult categories do not. This tool is for adults.
- Pregnancy changes the meaning of weight gain entirely; use obstetric guidance rather than BMI targets during gestation.
Frequently asked questions
BMI = weight (kg) ÷ height² (m). In imperial units: BMI = 703 × pounds ÷ inches². The result maps to standard WHO adult categories.
Below 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30–34.9 obesity class I, 35–39.9 class II, and 40+ class III. Asian populations are sometimes assessed with lower overweight cutoffs.
Not always. BMI cannot distinguish muscle from fat, so muscular people can read overweight and older adults can read normal while carrying excess fat. It is a screening tool, not a diagnosis.
Body Surface Area, estimated with the Du Bois formula (√(cm × kg / 3600)), is used in medicine for certain drug dosing and cardiac indices.
The tool computes it as BMI 18.5 to 24.9 multiplied by your height squared. For 170 cm, that is roughly 53.5 to 72 kg.