BMI Calculator
Editorial Review
Reviewed for plain-language health guidance and calculator limitations by DP Tech Studio.
Reference sources
Important: BMI is a screening measure only and should not be treated as a diagnosis or a substitute for medical advice.
What is BMI?
Body Mass Index (BMI) is a simple numerical measure derived from a person's weight and height. It is widely used by healthcare professionals as an initial screening tool to categorise individuals into weight status groups: Underweight, Normal weight, Overweight, and Obese. A single BMI value does not diagnose health conditions, but it provides a useful quick reference for assessing weight-related health risks.
BMI Formula
Imperial: BMI = (Weight (lbs) / Height (in)²) × 703
The calculator accepts both metric (kilograms and centimetres) and imperial (pounds, feet, and inches) inputs, converting automatically to produce your BMI.
BMI Categories (WHO Standard)
18.5 – 24.9 — Normal weight
25.0 – 29.9 — Overweight
30.0 and above — Obese
Example Calculation
Height: 170 cm (1.70 m)
BMI = 70 / (1.70)² = 70 / 2.89 = 24.2 — Normal weight
Important Notes
- Screening only — BMI is a screening tool, not a diagnostic measure. Consult a doctor for a full health assessment.
- Does not distinguish fat from muscle — Athletes may have a high BMI due to muscle mass, not excess fat.
- Age and sex — BMI ranges may differ for children, elderly individuals, and pregnant women.
- Ethnicity — Some health bodies use adjusted cutoffs for different ethnic groups.
Understanding Your BMI Result in Context
BMI gives you a starting point, but its meaning varies depending on who you are:
- Children and adolescents — Use BMI-for-age percentiles rather than fixed adult cutoffs. Growth rates and body composition change rapidly during development.
- Older adults (65+) — A slightly higher BMI (23–27) is sometimes associated with better outcomes in older populations because body composition shifts with age.
- Pregnant women — BMI is not meaningful during pregnancy. Healthcare providers use separate weight-gain guidance based on pre-pregnancy weight.
- Highly muscular individuals — Lean muscle mass is denser than fat. Athletes and strength trainers often register as "overweight" on the BMI scale despite low body fat.
The History of BMI
BMI was invented in the 1830s by Belgian mathematician Adolphe Quetelet as a statistical tool to describe population averages — not to assess individual health. It wasn't widely adopted in clinical settings until the 1970s, when Ancel Keys published a study confirming its usefulness as a population-wide obesity indicator.
Today, health organisations worldwide use it as a first-line screening measure precisely because it requires only two easily measured values (weight and height) and no specialised equipment. More advanced measures like DEXA scans, waist-to-hip ratios, and skinfold calipers add precision but are far less practical for routine screening.