BMI Calculator
Calculate your BMI (Body Mass Index) using metric or imperial units. See your weight category and health classification.
• Underweight: BMI < 18.5
• Normal: 18.5 – 24.9
• Overweight: 25 – 29.9
• Obese: BMI ≥ 30
What is BMI Calculator?
A BMI (Body Mass Index) calculator computes a simple health metric based on your height and weight. BMI = weight(kg) / height(m)². It categorizes results as underweight (<18.5), normal weight (18.5-24.9), overweight (25-29.9), or obese (30+). While BMI doesn't account for muscle mass, bone density, or body composition (an athlete may have a high BMI due to muscle), it remains the most widely used screening tool by healthcare providers for identifying potential weight-related health risks in general populations. It's a starting point, not a diagnosis.
How It Works
Enter your weight and height in either metric (kg/cm) or imperial (lbs/feet+inches) units. The tool converts to metric if needed, then calculates BMI using the standard formula: weight in kilograms divided by height in meters squared. It displays your BMI value, the WHO classification category, and a visual indicator showing where you fall on the healthy weight spectrum. The tool also shows the healthy weight range for your height so you can see the target range. Results are immediate and update as you change inputs.
Examples
70 kg, 1.75 m
BMI = 70 / 1.75² = 22.9 Category: Normal weight (18.5–24.9)
180 lb, 5 ft 10 in (70 in)
BMI = 180 × 703 / 70² = 25.8 Category: Overweight (25–29.9)
Quick Reference
| Category | BMI range | Notes |
|---|---|---|
| Underweight | Below 18.5 | May indicate undernutrition; needs clinical context |
| Normal weight | 18.5 - 24.9 | Lower ceiling (~23) advised for some Asian populations |
| Overweight | 25.0 - 29.9 | Athletes often land here despite low body fat |
| Obesity class I | 30.0 - 34.9 | |
| Obesity class II | 35.0 - 39.9 | |
| Obesity class III | 40.0 and above |
Common Use Cases
- •Getting a quick health screening metric during personal fitness planning and goal setting
- •Tracking BMI changes over time as part of a weight management program
- •Understanding where you fall on the WHO weight classification scale
- •Calculating target weight ranges based on your height for general health goals
- •Preparing health information for insurance applications or wellness program requirements
- •Educational purposes — understanding the relationship between height, weight, and health metrics
Frequently Asked Questions
What is a healthy BMI?▼
A BMI between 18.5 and 24.9 is considered normal weight. Below is underweight, above is overweight.
How is BMI calculated?▼
Weight in kilograms divided by height in metres squared. For imperial units, multiply pounds by 703 and divide by height in inches squared. A 70 kg person 1.75 m tall has a BMI of 70 ÷ 1.75² = 22.9.
What are the standard BMI categories?▼
The WHO classification puts underweight below 18.5, normal weight from 18.5 to 24.9, overweight from 25 to 29.9, and obesity at 30 and above. Lower thresholds are recommended for some Asian populations, where health risks appear at a lower BMI.
What are the limitations of BMI?▼
It is a population screening measure, not a diagnosis, and it takes no account of body composition. Muscle is denser than fat, so athletes frequently register as overweight while carrying very little fat. It also ignores fat distribution, which is a stronger risk indicator than total mass, and it is less meaningful for children, pregnant women, and older adults who have lost muscle.
Is BMI calculated differently for children?▼
Yes. The same formula is used but the result is interpreted against age- and sex-specific percentile charts rather than fixed categories, because healthy body composition changes throughout growth. A child's BMI is reported as a percentile, not a category.
What is a better measure than BMI?▼
Waist circumference and waist-to-height ratio capture abdominal fat, which correlates more closely with metabolic risk. Keeping your waist under half your height is a simple, widely cited guide. Body fat percentage is more informative still but needs proper measurement.
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