BMI Calculator
More than 2 million people visit a “BMI calculator” page each day to quickly check whether their weight falls within a healthy range. Body mass index (BMI) is a simple screening tool that estimates body fat based on your height and weight. It doesn’t measure body fat directly, but years of research show it reliably flags potential weight‑related health risks for most adults.
Use the free calculator on this page to get your BMI instantly – just enter your measurements, and the tool does the rest.
Your BMI:
Remember: BMI is just one health indicator. For a complete evaluation and personalized recommendations, consult a healthcare professional.
How Is BMI Calculated?
BMI uses a straightforward formula that relates weight to height squared. The result is a single number that places you into one of four main categories: underweight, healthy weight, overweight, or obesity.
Metric formula
BMI = weight (kg) ÷ height² (m²)
Imperial formula
BMI = [weight (lb) ÷ height² (in²)] × 703
Example
A person who weighs 70 kg and is 1.75 m tall:
70 ÷ (1.75 × 1.75) = 22.86 → healthy weight range.
The calculator above accepts both metric (kilograms, centimeters) and imperial (pounds, feet) inputs. After you enter your height and weight, it computes your BMI and highlights the corresponding WHO‑recognized category.
WHO BMI Categories for Adults
The World Health Organization (WHO) defines the following cut‑off points for adults aged 20 and older. These values apply to men and women alike and are the standard used by most health authorities worldwide.
| Category | BMI (kg/m²) |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese (Class I) | 30.0 – 34.9 |
| Obese (Class II) | 35.0 – 39.9 |
| Obese (Class III) | 40.0 and above |
When your result appears, the calculator also displays a color‑coded bar so you can see at a glance where your number falls within these ranges.
What a BMI Number Tells You
A high BMI is linked to an increased chance of developing heart disease, type 2 diabetes, high blood pressure, and certain cancers. A very low BMI can signal malnutrition, weakened immunity, or an underlying condition. However, BMI is a population‑level tool; it doesn’t account for muscle mass, bone density, or fat distribution in an individual.
For this reason, doctors often combine BMI with other measures – like waist circumference, blood tests, and family history – to make a full health assessment.
BMI for Children and Teens
Interpreting BMI for children (ages 2–19) is different. Because their bodies are still growing, the calculation uses age‑ and sex‑specific percentiles based on CDC growth charts.
- Underweight: less than the 5th percentile
- Healthy weight: 5th to less than 85th percentile
- Overweight: 85th to less than 95th percentile
- Obesity: 95th percentile or above
Our calculator includes the option to select a child’s age and sex, and it automatically references the correct percentile curves.
Why the BMI Formula Doesn’t Suit Everyone
BMI has known limitations, especially for:
- Athletes and bodybuilders – high muscle mass can push BMI into the “overweight” or “obese” range while the person has very low body fat.
- Older adults – muscle loss often leads to a lower BMI that hides excess fat.
- Pregnant people – weight gain during pregnancy is normal and not captured by standard BMI categories.
- Certain ethnic groups – some populations have higher health risks at a lower BMI; for example, people of South Asian descent may develop diabetes at a BMI of 23, which is still in the “healthy” range.
If you belong to one of these groups, talk to a healthcare provider about whether additional tests are right for you.
How to Maintain a Healthy BMI
Reaching and staying in the 18.5–24.9 range isn’t just about the number on a scale; it’s about long‑term habits.
- Move more – aim for 150 minutes of moderate aerobic activity each week, such as brisk walking or cycling.
- Monitor your waistline – even a 5–10% weight loss can significantly lower blood pressure and cholesterol.
- Choose nutrient‑dense foods – fill half your plate with vegetables, a quarter with whole grains, and a quarter with lean protein.
- Sleep well – consistent 7–9 hours a night helps regulate hunger hormones.
- Recheck periodically – use the calculator every few months to track changes, but don’t obsess over daily fluctuations.
This article is for informational purposes only and does not replace professional medical advice. Always consult your doctor before making changes to your diet or exercise routine.