Jump to the free BMI calculator
What is BMI?
Body Mass Index (BMI) is a simple screening tool that estimates body fat based on your height and weight. While it doesn’t measure body fat directly, it provides a useful starting point for assessing whether your weight falls within a healthy range.
The BMI Formula
Metric system:
BMI = Weight (kg) / Height (m)²
Imperial system:
BMI = (Weight (lbs) / Height (in)²) × 703
Step-by-Step Example
Metric
For a person who is 175 cm tall and weighs 70 kg:
Height in meters = 175 / 100 = 1.75 m
BMI = 70 / (1.75 × 1.75)
BMI = 70 / 3.0625
BMI = 22.9
Imperial
For a person who is 5'9" (69 inches) and weighs 160 lbs:
BMI = (160 / (69 × 69)) × 703
BMI = (160 / 4761) × 703
BMI = 0.0336 × 703
BMI = 23.6
BMI Categories
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
Important Limitations
BMI is a useful general indicator, but it has limitations:
- Doesn’t distinguish between muscle and fat (athletes may show high BMI despite low body fat)
- Doesn’t account for age, sex, or ethnicity differences
- Not designed for children, pregnant women, or elderly individuals
- Not a diagnostic tool — always consult a healthcare provider
Other useful metrics to consider alongside BMI include waist circumference, body fat percentage, and waist-to-hip ratio.
If you need to convert between metric and imperial units for your measurements, try our free unit converter.
Free BMI Calculator
Calculate your BMI using either metric or imperial units.
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Frequently Asked Questions
What is a healthy BMI range?
A healthy BMI falls between 18.5 and 24.9 according to the World Health Organization. However, BMI is just one screening tool and does not account for muscle mass, bone density, age, or sex. Always consult a healthcare provider for a complete assessment.
Is BMI accurate for athletes?
BMI can be misleading for athletes and muscular individuals. Since muscle weighs more than fat, a highly trained athlete may have a high BMI while having very low body fat. In these cases, body fat percentage or waist-to-hip ratio are more useful metrics.
How often should I check my BMI?
For most adults, checking BMI once every few months is sufficient. Tracking it over time can help you notice trends. Pair it with other health indicators for a more complete picture.
Calculate BMI in Notes Calculator
Notes Calculator has built-in unit conversions and variables, making it ideal for health calculations. Here’s how a BMI calculation looks in the app:
# BMI Calculator
weight = 70 kg
height = 175 cm
height in m
BMI = weight / (height in m) ^ 2
The app converts 175 cm to meters automatically when you type height in m, and variables like weight and height let you tweak values and see your BMI update in real time. You can convert between imperial and metric on the fly — type 160 lbs in kg or 69 inches in cm to switch systems instantly.
Use headings (#) to organize your notes, and tabs to keep separate calculations for different health metrics.