BMI Calculator
Calculate your Body Mass Index (BMI) instantly from height and weight. Free, fast, no signup.
How to use this tool
- Enter weight, height and target bmi (for goal weight) in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your bmi and the full breakdown beneath it.
Body Mass Index (BMI) estimates body fat from your height and weight. Enter your numbers to get your BMI and category instantly.
⚠ This tool is for general information and education only and is not medical advice. Consult a qualified healthcare professional before making health decisions.
Formula
BMI = weight (kg) ÷ height (m)2
Where height in metres = height (cm) ÷ 100.
How it works
This calculator divides your weight in kilograms by the square of your height in metres to produce a dimensionless Body Mass Index score. Categories follow the standard WHO thresholds: below 18.5 Underweight, 18.5–24.9 Normal weight, 25–29.9 Overweight, and 30 or above Obese.
BMI is a population-level screening tool and does not directly measure body fat; it can misclassify muscular individuals and is less reliable at the extremes of age. Use it as a starting point, not a clinical diagnosis.
Worked example
- Convert height to metres: 175 cm ÷ 100 = 1.75 m.
- Square the height: 1.75 × 1.75 = 3.0625 m².
- Divide weight by squared height: 70 ÷ 3.0625 = 22.86 (rounded to 2 decimal places).
- Look up the WHO category for 22.86: falls between 18.5 and 25 → Normal weight.
BMI = 22.86, Category = Normal weight
Common mistakes to avoid
- Using height in centimeters directly instead of converting to meters first -- dividing 175 cm by 100 before squaring is mandatory.
- Squaring only the unit rather than the full height value: computing weight / height and then squaring the result instead of squaring height first.
- Interpreting BMI categories universally -- the standard 18.5-24.9 healthy range was calibrated on European populations and may misclassify Asian or very muscular individuals.
Key terms
- BMI (Body Mass Index)
- A number derived from weight and height used to screen for weight categories that may lead to health problems.
- Underweight
- A BMI below 18.5, indicating body weight may be too low relative to height.
- Overweight
- A BMI between 25 and 29.9, suggesting body weight is above the normal range for the given height.
- Obese
- A BMI of 30 or above, associated with increased risk of metabolic and cardiovascular conditions.
- WHO thresholds
- The World Health Organization's standardised BMI cut-off points used globally to define weight categories in adults.
Frequently asked questions
- What is a healthy BMI?
- A BMI between 18.5 and 24.9 is considered the healthy range for most adults.
- Is BMI accurate?
- BMI is a useful screening tool but does not account for muscle mass, so athletes may read high.