BMI Calculator
Health is more than a number, but numbers help us track it. Measure your Body Mass Index instantly to understand your weight relative to your height.
The First Metrics of Health
In a world of smart rings, continuous glucose monitors, and genetic testing, the Body Mass Index (BMI) remains the most widely used screening tool for weight categories. Why? Because it's simple, non-invasive, and provides a quick "snapshot" of whether your weight is appropriate for your frame.
Our BMI Calculator takes the math out of the equation. Whether you use pounds or kilograms, feet or meters, we standardize the data to give you a clear answer based on World Health Organization (WHO) guidelines.
Interpreting the Numbers
The result you get is a unitless number (kg/m²). Here is how doctors generally categorize it:
Underweight (< 18.5)
Being underweight can be a sign of malnutrition or underlying health issues. It may weaken the immune system.
Normal Weight (18.5 – 24.9)
This range is statistically associated with the lowest risk of weight-related diseases like Type 2 Diabetes and heart disease.
Overweight (25 – 29.9)
Carrying excess weight may increase the risk of cardiovascular issues. Lifestyle changes are often recommended.
Obesity (30+)
Divided into Class I, II, and III. This category correlates strongly with high blood pressure, diabetes, and joint problems.
The Formula Behind the Tool
BMI was invented by Adolphe Quetelet in the 1830s. The math is surprisingly simple:
If you use pounds and inches, the formula includes a conversion factor: (Weight lbs / Height in²) x 703. Our calculator handles these conversions automatically so you don't have to navigate the math.
⚠️ The "Muscle Paradox" (Limitations)
BMI is a useful population-level metric, but it is flawed at the individual level. It assumes that weight comes from fat.
Example: An NFL linebacker might be 6'3" and 250lbs of pure muscle. His BMI would be 31.2 (Obese). However, he is likely rigorous healthy. Conversely, an elderly person might have a "Normal" BMI but very low muscle mass ("skinny fat"), which carries its own health risks. Always consult a doctor for a true health assessment.
Goal Setting
Trying to get in shape? Don't just track pounds lost. Track your movement into a healthier BMI category to visualize the reduction in health risk.
Insurance Screenings
Many life insurance policies use BMI bands to determine premiums. Knowing your number beforehand helps you understand potential costs.
Clothing Fit
While not a size guide, BMI provides a general frame of reference for body composition when shopping for brands with different sizing charts.
Frequently Asked Questions
Is BMI the same for men and women?
The formula is the same. However, women statistically carry more body fat than men at the same BMI level. Doctors often interpret the risk factors slightly differently based on gender.
Why is waist circumference important?
Waist measurement tracks visceral fat (belly fat), which is more dangerous for heart health than subcutaneous fat (under skin). Combining BMI with waist measurement is a better predictor of health.
Can I use this for my child?
You can use it to get the number, but do not use the adult categories (Underweight/Overweight) for kids. Children need to be compared against growth charts (Percentiles) for their specific age and gender.
Medical Disclaimer
This tool is for informational purposes only. It is not a medical diagnosis. Please consult a healthcare professional before making drastic diet or exercise changes.
Data Privacy
We do not store your weight or height data. This tool runs entirely in your browser.