BMI Calculator
Calculate your Body Mass Index and see what category you fall into.
BMI Categories
| Underweight | < 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obese | ≥ 30 |
BMI is a screening tool and does not diagnose body fatness or health. Athletes may have a high BMI due to muscle mass. Consult a healthcare provider for personalised advice.
What Is BMI?
Body Mass Index (BMI) is a simple screening measurement that uses your height and weight to estimate whether your weight falls into a healthy range. It's used by health organizations worldwide, including the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC), as a population-level screening tool for weight categories.
BMI doesn't measure body fat directly — it's a quick, low-cost proxy that correlates reasonably well with body fat for most adults, which is why it remains widely used in clinical and public health settings despite its limitations.
How BMI Is Calculated
BMI is calculated by dividing your weight by the square of your height. This calculator uses the standard formulas below:
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 falls in the "Normal weight" category.
Healthy BMI Ranges
The table above shows the four standard adult BMI categories used by the WHO and CDC. These ranges apply to adults aged 20 and over and are the same for men and women, though individual healthy weight can vary based on muscle mass, frame size, age, and ethnicity.
BMI vs. Body Fat
Because BMI only uses height and weight, it can't distinguish muscle from fat. A muscular athlete can have a "high" BMI while having very low body fat, while someone with a "normal" BMI could still carry a high proportion of body fat. If you want a more direct estimate of body composition, try our Body Fat Calculator, which uses the U.S. Navy tape-measure method.
Limitations of BMI
- Does not account for muscle mass, bone density, or body composition
- May overestimate body fat in athletes and very muscular individuals
- May underestimate body fat in older adults who've lost muscle mass
- Standard ranges are less reliable for children, teenagers, and pregnant women
- Doesn't reflect where fat is distributed on the body, which also affects health risk
Because of these limitations, BMI is best used as a starting point for a conversation with a healthcare provider, not as a standalone diagnosis. Tools like our Waist-to-Hip Ratio Calculator and Body Fat Calculator can add helpful context alongside BMI.
Frequently Asked Questions
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is classified as "normal weight" by the WHO and CDC. Below 18.5 is considered underweight, 25–29.9 is overweight, and 30 or above is classified as obese.
Is BMI accurate for everyone?
No. BMI is a useful population-level screening tool, but it doesn't measure body fat directly and can be less accurate for athletes, older adults, and people with unusually high or low muscle mass. It is not intended as an individual diagnostic tool.
Does BMI differ for men and women?
The standard BMI formula and category ranges are the same for adult men and women. However, women naturally tend to carry a higher percentage of body fat than men at the same BMI, which is one reason BMI is best interpreted alongside other measurements.
Can I use BMI for children?
Adult BMI categories don't apply to children and teenagers. Pediatric BMI is calculated the same way but interpreted using age- and sex-specific percentile charts, so this calculator is intended for adults aged 20 and over.
What should I do if my BMI is outside the normal range?
Treat it as a starting point, not a diagnosis. Consider your body composition, activity level, and overall health, and speak with a healthcare provider for personalised guidance, especially if your BMI is significantly outside the normal range.
Sources
- World Health Organization — Obesity and overweight
- CDC — About Adult BMI
- NIH National Heart, Lung, and Blood Institute — BMI Calculator
Last reviewed: September 2026. This page is for informational purposes only and is not a substitute for professional medical advice.