Use this BMI Calculator to calculate your body mass index from your height and weight in seconds. It also interprets the number using widely used BMI categories so you can understand whether your BMI falls in underweight, normal weight, overweight, or obesity ranges.
What BMI Means (and What It Doesn’t)
Body Mass Index (BMI) is a screening measure that relates body weight to height. It helps identify general weight categories that correlate with health risks at a population level.
BMI is useful for quick comparisons, but it is not a direct measure of body fat. People with very muscular builds, older adults, athletes, and pregnant individuals may have BMI values that do not perfectly reflect body fat or health risk.
BMI Formula You’ll Use
The BMI formula depends on the unit system. The calculator applies the correct math automatically based on your inputs.
Metric formula (kg and m)
BMI = weight (kg) / [height (m)]²
- Convert centimeters to meters by dividing by 100.
- Square the height in meters.
Imperial formula (lb and in)
BMI = (weight (lb) / [height (in)]²) × 703
- Use inches for height and pounds for weight.
- The constant 703 converts the units to make BMI comparable.
BMI Categories (Adult, Standard Ranges)
After you calculate BMI, you can interpret it using standard adult categories.
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Normal weight |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obesity |
These ranges are designed for adults. For children and teens, BMI is interpreted differently using age- and sex-specific percentiles.
How to Measure Height and Weight for Accurate Results
Small measurement errors can shift your BMI category, so use consistent methods.
- Height: Stand straight without shoes. For best accuracy, measure at the same time of day.
- Weight: Weigh with minimal clothing. Use the same scale if possible.
- Units: Enter the units you actually measured (cm vs in, kg vs lb). The calculator handles conversions, but you must input correctly.
Using the BMI Calculator (Step-by-Step)
- Enter your height and choose the correct unit (cm/in).
- Enter your weight and choose the correct unit (kg/lb).
- Click Calculate BMI.
- Read the result and the category shown below.
- If needed, adjust inputs and recalculate to see how changes affect your BMI.
The calculator computes BMI using the standard formula and then maps the value to the adult category ranges.
Practical Examples: Real-World Use Cases
Example 1: Quick health screening
Jordan is 175 cm tall and weighs 72 kg. The BMI Calculator converts height to meters, squares it, divides weight by the squared height, and returns a BMI that falls in the normal weight range. Jordan uses the result as a starting point for lifestyle goals, not as a diagnosis.
Example 2: Tracking progress over time
Sam is 5 ft 10 in and weighs 210 lb. After a few months of consistent changes, Sam weighs 195 lb but keeps the same height. Recalculating BMI shows whether the number moved into a lower category, which can help motivate continued progress.
Common Questions About BMI
Frequently Asked Questions
What is a BMI Calculator and how does it work?
A BMI Calculator computes body mass index using your height and weight. It converts your units if needed, then applies the standard BMI formula for metric or imperial measurements. The result is compared to adult BMI ranges to label underweight, normal weight, overweight, or obesity.
Is BMI the same for men and women?
For adults, BMI categories use the same cutoffs for men and women. The calculation itself does not include sex. However, health risk can vary by body composition and fat distribution, so BMI is a screening tool, not a complete health assessment.
How accurate is BMI for estimating health risk?
BMI is reasonably useful for large groups, but it cannot directly measure body fat. It may misclassify muscular individuals or people with different body shapes. For a fuller picture, combine BMI with waist measurements, blood pressure, cholesterol, and glucose testing.
Should children and teens use the same BMI categories?
No. Children and teens use BMI-for-age percentiles because growth changes body composition over time. A number that is “normal” for one age may be different at another age. Clinicians typically use CDC or WHO growth charts for interpretation.
What should I do if my BMI is in an unhealthy range?
If your BMI falls in an underweight, overweight, or obesity range, consider talking with a healthcare professional. They can assess diet, activity, medical history, and other risk factors. Small, sustained changes in nutrition and exercise often improve BMI and overall health.
Limitations and When to Seek Medical Advice
BMI does not account for muscle mass, fat distribution, age-related changes, or ethnicity-specific differences. It also cannot confirm a diagnosis.
If you have symptoms, a known medical condition, or you’re an athlete, older adult, or pregnant, use BMI as one data point. For personal guidance, consult a clinician or registered dietitian.
Bottom Line
The BMI Calculator gives you a fast, standard BMI number from height and weight. Use it to understand your category and guide next steps, then rely on additional health measures for decisions.