BMI calculator
Calculate your body mass index and see your healthy weight range. Supports metric (cm/kg) and imperial (ft/lb) units.
BMI categories (WHO / NHS / CDC)
- Below 18.5 — Underweight
- 18.5 to 24.9 — Healthy weight
- 25 to 29.9 — Overweight
- 30 and above — Obesity
The marker on the scale above shows exactly where your result falls between these four bands.
What BMI doesn't measure
BMI is a quick, free screening tool used by doctors worldwide because it correlates reasonably well with body fat at a population level — but it only uses height and weight, so it can't tell muscle from fat. A muscular athlete can show as "overweight" despite having low body fat, while someone with low muscle mass can have a "healthy" BMI but a high body fat percentage. See our BMI vs body fat comparison for a deeper look, and our ideal weight for your height guide for more context.
- Athletes and very muscular people — BMI often overestimates body fat.
- Older adults — BMI can underestimate body fat as muscle mass naturally declines with age.
- Pregnant women — weight gain is expected and healthy; BMI categories don't apply during pregnancy.
Frequently asked questions
What is a healthy BMI?
For most adults, 18.5 to 24.9 is considered healthy by the WHO, CDC and NHS.
How is BMI calculated?
Weight in kilograms divided by height in metres squared (kg/m²). In imperial: (lb ÷ in²) × 703.
Is BMI accurate for everyone?
It's a screening tool, not a diagnosis. Muscular athletes, older adults and pregnant women should interpret it with care.
What should I do if my BMI is outside the healthy range?
Treat it as a starting point for a conversation with a doctor or dietitian, not a verdict — they can assess body composition, health markers and context BMI can't see.
This tool is for information only and is not medical advice. Consult a health professional about your weight or health.