How to Calculate BMI and What It Means
BMI, or Body Mass Index, is a simple number that estimates whether your weight is in a healthy range for your height. Doctors and health websites use it as a quick screening tool. Here's how it's calculated and how to interpret your result.
The BMI formula
In metric units:
BMI = weight (kg) ÷ [ height (m) × height (m) ]
For example, someone who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which is in the healthy range.
BMI categories (adults)
- Below 18.5 — Underweight
- 18.5 to 24.9 — Normal / healthy weight
- 25 to 29.9 — Overweight
- 30 and above — Obese
Step-by-step: calculate your BMI
- Open the BMI Calculator.
- Choose metric (kg, cm) or imperial (lb, in) units.
- Enter your weight and height.
- Click Calculate to see your BMI and category instantly.
The limitations of BMI
BMI doesn't distinguish between muscle and fat. A very muscular athlete may have a high BMI while being perfectly healthy, and BMI can be less accurate for older adults, pregnant women and different body types. Treat it as one useful indicator among several, alongside waist measurement and overall fitness.
Using BMI wisely
Rather than focusing on a single number, track trends over time and combine BMI with healthy habits: balanced eating, regular activity and good sleep. Small, consistent changes matter far more than any one measurement.
Frequently Asked Questions
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered healthy. Below that is underweight, and above it is overweight or obese.
Is BMI accurate for athletes?
Not always. Muscle weighs more than fat, so very muscular people can have a high BMI while being extremely fit. In such cases, body-fat percentage is a better measure.
Is BMI different for men and women?
The formula and adult categories are the same for both. However, women naturally carry slightly more body fat, so BMI is best used as a general guide.
Does BMI work for children?
Children and teenagers use age- and sex-specific BMI percentile charts rather than the fixed adult ranges, so consult a paediatric chart or doctor.
How can I improve my BMI?
Focus on sustainable habits: balanced meals, regular activity, enough sleep and reduced sugary drinks. Gradual change is healthier and lasts longer than crash diets.
Try the BMI Calculator