BMI (Body Mass Index) is the world's most widely used screening measure for weight-related health risk. It distills your height and weight into a single number — weight in kilograms divided by height in meters squared — and places you in one of four categories: underweight (below 18.5), healthy (18.5–24.9), overweight (25–29.9), or obesity (30+).
Doctors, insurers, and fitness programs use BMI because it is simple, fast, and correlates well with body-fat-related risk at the population level. Our calculator supports both metric and imperial units and also shows the healthy weight range for your exact height, so you get a target — not just a label.
One honest caveat: BMI cannot tell muscle from fat. Very muscular people, athletes, and the elderly can get misleading readings. Treat BMI as a screening tool and starting point, and pair it with waist measurements or a body-fat estimate for the full picture.
How to use the BMI Calculator
- Choose your units: metric (kg/cm) or imperial (lb/in).
- Enter your current weight — weigh yourself in the morning for consistency.
- Enter your height without shoes.
- Click Calculate BMI to see your score, category, and healthy weight range.
Tips for accurate results
- Weigh yourself at the same time of day, ideally mornings before eating.
- BMI is less accurate for athletes, pregnant women, children, and adults over 65.
- Track the trend over months — a single reading matters less than the direction.
- Pair BMI with waist circumference for a better health-risk picture.
What your BMI means
The standard adult cutoffs come from the World Health Organization: under 18.5 may signal undernutrition; 18.5–24.9 is associated with the lowest health risk; 25–29.9 suggests excess weight; 30 and above indicates obesity, linked to higher risk of heart disease, type 2 diabetes, and joint problems. Small, sustained changes — not crash diets — move the number safely.
Frequently asked questions
What is a good BMI?
A BMI between 18.5 and 24.9 is considered the healthy range for most adults, associated with the lowest risk of weight-related disease.
How is BMI calculated?
BMI = weight (kg) ÷ height (m)². In imperial units: BMI = 703 × weight (lb) ÷ height (in)².
Is BMI accurate for muscular people?
Not always. Muscle is denser than fat, so muscular individuals can score as ‘overweight’ while being very lean. Athletes should use body-fat percentage instead.
How often should I check my BMI?
Monthly is plenty. Weight fluctuates daily with water and food, so trends over weeks and months are what matter.