Tools Health & Lifestyle BMI Calculator
Health & Lifestyle

BMI Calculator

Calculate your Body Mass Index and understand what it means for your health — in metric or imperial units.

Healthy lifestyle tips

  • BMI is one data point among many. Waist circumference, muscle mass, blood pressure, and resting heart rate give a fuller picture of health than any single number.
  • Sustainable habits beat short-term changes: small, consistent actions like 30 minutes of daily movement and adequate sleep create long-term health improvements without deprivation.
  • Strength training preserves muscle mass (which BMI ignores) and improves metabolic health, bone density, and mood — especially important as we age.
  • If you're concerned about your weight or health metrics, a GP, dietitian, or accredited exercise physiologist can provide personalised, evidence-based guidance.

Understanding BMI and its limitations

Body Mass Index (BMI) is calculated from height and weight alone. It was developed in the 19th century as a population-level statistical tool and is still used today as a quick screening measure because it's simple and requires no equipment. However, it has well-known limitations: it cannot distinguish between fat and muscle, doesn't account for age or body composition, and may be less accurate for certain ethnic groups.

A muscular athlete may have a "overweight" BMI while being in excellent health; an older person with low muscle mass may have a "normal" BMI despite having too much body fat. Use BMI as a starting point, not a verdict.

Frequently asked questions

What is BMI?
BMI (Body Mass Index) is a ratio of weight to height squared (kg/m² or 703×lbs/in²). It was developed by Adolphe Quetelet in the 1830s to describe average body size in populations. Today, health organisations use it as a quick screening tool to categorise individuals as underweight, normal weight, overweight, or obese — while acknowledging its significant limitations as an individual health measure.
Is BMI accurate?
BMI is a reasonable population-level tool but imprecise at the individual level. It overestimates fat in muscular people (athletes, strength trainers) and underestimates fat in people with low muscle mass. Research suggests BMI misclassifies up to 30% of individuals. More accurate but expensive methods include DEXA scans and hydrostatic weighing for body fat percentage.
What's a healthy BMI?
According to the WHO, a BMI of 18.5–24.9 is classified as "normal weight" for adults. However, healthy BMI ranges can differ by ethnicity — some Asian health organisations use a lower threshold of 23 for "overweight." For older adults, a slightly higher BMI (23–27) is associated with better health outcomes. Always interpret BMI alongside other health indicators.

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