Body Mass Index (BMI) is one of the most widely used health screening tools in the world. Whether you're trying to lose weight, maintain a healthy lifestyle, or simply understand your body better, knowing how to calculate your BMI is an essential first step.
In this complete guide, we'll explain the BMI formula, walk you through calculations step by step, and help you understand what your results actually mean for your health.
What is BMI?
BMI stands for Body Mass Index. It's a simple calculation using your height and weight to estimate whether you have a healthy body weight. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and is now used by doctors worldwide.
BMI is not a perfect measure of health — it doesn't account for muscle mass, bone density, or fat distribution — but it's a useful screening tool for identifying potential weight-related health risks.
BMI Formula
Metric (kg & cm)
Example: Weight = 70 kg, Height = 1.75 m
BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9
Imperial (lbs & inches)
Example: Weight = 154 lbs, Height = 5'9" (69 inches)
BMI = (154 × 703) ÷ (69 × 69) = 108,262 ÷ 4,761 = 22.7
BMI Categories
The World Health Organization (WHO) classifies BMI into these categories:
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Malnutrition risk |
| 18.5 – 24.9 | Normal / Healthy | Low risk |
| 25.0 – 29.9 | Overweight | Moderate risk |
| 30.0 – 34.9 | Obese Class I | High risk |
| 35.0 – 39.9 | Obese Class II | Very high risk |
| 40.0 and above | Obese Class III | Extremely high risk |
Limitations of BMI
While BMI is a useful screening tool, it has important limitations:
- Athletes and bodybuilders may have a high BMI due to muscle mass, not fat
- Older adults may have a normal BMI but still have excess body fat
- Different ethnicities may have different health risks at the same BMI
- BMI does not measure where fat is stored (belly fat is more risky)
How to Reach a Healthy BMI
If your BMI is outside the healthy range, here are evidence-based steps:
- Calculate your daily calorie needs using our Calorie Calculator
- Create a moderate calorie deficit of 300–500 calories per day for weight loss
- Exercise regularly — aim for 150 minutes of moderate activity per week
- Track your progress — check your BMI monthly using our BMI Calculator
⚖️ Calculate Your BMI Now — It's Free!
Use our free BMI calculator to find your exact BMI in seconds. Supports both imperial (lbs/ft) and metric (kg/cm).
Try Free BMI Calculator →Frequently Asked Questions
Is BMI accurate for women and men?
The same BMI formula applies to both men and women, but women naturally have more body fat than men at the same BMI. The healthy range (18.5–24.9) applies to both sexes.
What is a healthy BMI for seniors over 65?
Some research suggests that a slightly higher BMI (22–27) may be healthier for older adults, as it provides protection against bone loss and illness recovery.
How often should I check my BMI?
Checking your BMI once a month is sufficient for tracking progress. Daily weight fluctuations are normal and don't reflect actual fat changes.