BMI Calculator — Body Mass Index
Free BMI calculator — compute your body-mass index from height and weight in metric or imperial units, with WHO weight category.
BMI categories (WHO)
- Below 18.5 — Underweight
- 18.5 – 24.9 — Normal weight
- 25.0 – 29.9 — Overweight
- 30.0 and above — Obesity
BMI = weight (kg) ÷ height² (m²). It's a quick population-level screen, not a diagnosis — muscle mass, age and body composition all matter. Talk to a medical professional for individual guidance.
Frequently asked questions
What is a healthy BMI?
The WHO defines 18.5–24.9 as the normal range for adults. Below 18.5 is underweight, 25–29.9 is overweight and 30+ is classed as obesity.
How is BMI calculated?
BMI = weight in kilograms ÷ height in metres squared. For imperial inputs this tool converts to metric first (inches × 0.0254, pounds × 0.4536).
Is BMI accurate for athletes and seniors?
It has limits — muscular people can read “overweight” with low body fat, and BMI doesn't capture fat distribution or age. Treat it as a quick screen, not a diagnosis, and consult a professional for individual advice.
Is this BMI calculator free?
Yes — free, no sign-up, and your height and weight never leave your browser.