How to Use the BMI Calculator
Height and weight only — the adult BMI formula does not need age or sex.
- Choose Metric (cm, kg) or Imperial (ft, in, lb). Switching units converts values you already entered.
- Enter height and weight. Results update live — no submit button.
- Read your BMI to one decimal place, the category label, and the labeled scale marker.
- Optionally switch to Asian cut-offs if that guideline is relevant for you; Standard (WHO) remains the default.
How BMI Is Calculated
Body mass index is a ratio of weight to height squared.
Metric: BMI = weight (kg) ÷ [height (m)]². Example: a person who is 70 kg and 1.75 m tall has BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 ≈ 22.9.
Imperial: BMI = 703 × weight (lb) ÷ [height (in)]². The factor 703 converts the pound–inch system so the result matches the metric definition.
BMI Categories
Adult categories used by this calculator. Cut-offs can vary between organizations and countries.
| Category | Standard (WHO) BMI | Asian cut-offs BMI |
|---|---|---|
| Underweight | Less than 18.5 | Less than 18.5 |
| Normal weight | 18.5 – 24.9 | 18.5 – 22.9 |
| Overweight | 25.0 – 29.9 | 23.0 – 27.4 |
| Obesity (class I) | 30.0 – 34.9 | Obesity from 27.5 (single band in this guideline) |
| Obesity (class II) | 35.0 – 39.9 | — |
| Obesity (class III) | 40.0 or above | — |
Asian cut-offs follow commonly cited public-health action points (23.0 and 27.5). National guidelines may differ.
What BMI Can and Cannot Tell You
BMI is a screening tool, not a complete picture of health.
BMI estimates weight relative to height. It is widely used because it is simple and does not require specialized equipment. Public health agencies use category bands to describe populations, and clinicians may use BMI as one of several screening inputs.
BMI does not measure body fat directly. It does not show where fat is stored (for example around the waist), and it can be misleading for athletes with high muscle mass, for some older adults, and during pregnancy. It also does not replace blood pressure, blood tests, waist circumference, or a full clinical history.
For any decision about your health, talk to a qualified healthcare professional. This page does not diagnose conditions or recommend diets, calorie targets, or weight-change plans.
Frequently Asked Questions
Healthy BMI range, men vs women, athletes, children, and Asian cut-offs.
How do I calculate my BMI?
BMI is weight in kilograms divided by height in meters squared: BMI = kg ÷ m². In imperial units, an equivalent formula is BMI = 703 × lb ÷ in². Enter height and weight above — metric (cm, kg) or imperial (feet and inches, pounds) — and the calculator shows the result with a worked step.
What is a healthy BMI range?
For adults, the WHO normal-weight category is a BMI of 18.5 to 24.9. This tool also shows the weight range that corresponds to 18.5–24.9 for your height. BMI is only a screening measure; a healthcare professional can interpret it alongside other factors.
Is BMI different for men and women?
The BMI formula is the same for men and women. Adult WHO categories also use the same cut-offs for both. That is why this calculator has no sex field — sex does not change the BMI number or the standard adult category thresholds.
Is BMI accurate for athletes or muscular people?
Not always. BMI does not measure body fat directly. People with high muscle mass can have a higher BMI without high body fat, so the category may overestimate risk. Use BMI as one screening input and discuss results with a healthcare professional.
Does BMI work for children and teenagers?
No. For children and teens under 20, BMI is interpreted with age- and sex-specific percentiles, not the adult categories used here. This calculator does not provide pediatric percentiles — ask a doctor or pediatric clinician.
What BMI cut-offs are used for Asian populations?
A WHO expert consultation described public-health action points often applied as overweight from 23.0 and obesity from 27.5 for many Asian populations, while retaining WHO’s international categories. Individual countries and organizations may use slightly different cut-offs. Choose “Asian cut-offs” in the calculator for this alternative guideline.
Does BMI apply during pregnancy or for older adults?
BMI is less reliable in pregnancy and can be harder to interpret for older adults because body composition changes with age. Do not use this tool to make health decisions in those situations — speak with a qualified healthcare professional.
What are the limitations of BMI?
BMI does not measure body fat, fat distribution, muscle mass, bone density, or metabolic health. It can misclassify muscular athletes, overlook risks linked to waist circumference, and is not designed as a diagnosis. It is a quick screening number, not a full health assessment.
Sources
Adult BMI categories: CDC — Adult BMI Categories. Obesity and overweight overview: WHO — Obesity and overweight fact sheet. Asian public-health action points (23.0 / 27.5) are described in the WHO expert consultation published in The Lancet (2004).
This calculator provides general information and is not medical advice or a diagnosis. Talk to a qualified healthcare professional about your health.
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