BMI Calculator
Calculate Body Mass Index from weight and height.
BMI measurements
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Result
How to calculate bmi
Body Mass Index (BMI) is a simple screening measure that relates your weight to your height, used widely by health organizations as a quick, population-level indicator — not a diagnosis, but a starting point for a conversation about health with a medical professional.
How the calculation works
BMI = 703 × Weight (lb) ÷ Height (in)². This is the standard imperial-unit BMI formula, mathematically equivalent to the metric formula (weight in kg ÷ height in meters squared) with the 703 constant handling the unit conversion.
Example
A person who is 5'6" (66 inches) and weighs 150 lb: BMI = 703 × 150 ÷ 66² = 703 × 150 ÷ 4,356 ≈ 24.2. Under the standard CDC categories, this falls in the 'normal weight' range (18.5–24.9), just below the 'overweight' threshold of 25.
Frequently asked questions
Is BMI accurate for athletes or very muscular people?
Not reliably — muscle is denser than fat, so a muscular person can have a high BMI while having low body fat. BMI is a population-level screening tool and is known to be less accurate for people with unusually high muscle mass.
What are the standard BMI categories?
Under CDC/WHO adult standards: below 18.5 is underweight, 18.5–24.9 is normal weight, 25–29.9 is overweight, and 30 or above is classified as obese. These categories are population guidelines and don't account for individual variation.
Does BMI apply the same way to children?
No — children and teens are assessed using age- and sex-specific BMI percentiles rather than the fixed adult categories, since body composition changes significantly during growth.
BMI Calculator
BMI = 703 × Weight (lb) ÷ Height (in)². This is the standard imperial-unit BMI formula, mathematically equivalent to the metric formula (weight in kg ÷ height in meters squared) with the 703 constant handling the unit conversion.
Let's understand your bmi result.
Calculate a result above and this guide will help you interpret it using this calculator's own formula and explanation.
Pro Tips for BMI
- BMI doesn't distinguish between muscle and fat, so it can misclassify very muscular individuals as 'overweight' despite low body fat — it's most useful as a broad population screening tool, not an individual diagnosis.
- Track your own BMI trend over time rather than fixating on a single reading — the direction of change often matters more than the exact number for most people's health goals.
- Pair BMI with other measures (waist circumference, body fat percentage, or a conversation with a doctor) for a fuller picture, since BMI alone doesn't capture body composition or fat distribution.
Common BMI Mistakes to Avoid
- Treating BMI as a precise medical diagnosis rather than a screening estimate — it doesn't account for muscle mass, bone density, age, or sex-specific differences in body composition.
- Using outdated height or weight (e.g., from years ago) instead of current measurements, which produces a BMI that no longer reflects your actual status.
When to Use This Calculator
Body Mass Index (BMI) is a simple screening measure that relates your weight to your height, used widely by health organizations as a quick, population-level indicator — not a diagnosis, but a starting point for a conversation about health with a medical professional.