A BMI calculator (Body Mass Index calculator) instantly tells you your BMI based on your height and weight. It’s a widely used screening tool to categorize weight status — underweight, normal weight, overweight, or obese — and is available completely free online with no sign-up required.
What Is BMI?
BMI stands for Body Mass Index. It is calculated by dividing your weight in kilograms by the square of your height in metres (kg/m²). BMI was developed by Belgian mathematician Adolphe Quetelet in the 1830s and is now used globally by health professionals as a quick screening tool.
BMI Formula
| Unit System | Formula |
|---|---|
| Metric | BMI = weight (kg) ÷ height (m)² |
| Imperial | BMI = (weight (lbs) ÷ height (in)²) × 703 |
BMI Categories for Adults
| BMI Range | Weight Status |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obese (Class I) |
| 35.0 – 39.9 | Obese (Class II) |
| 40.0 and above | Severely Obese (Class III) |
How to Calculate BMI
- Open the free BMI calculator at ReadyGoTools
- Select your unit system: metric (kg/cm) or imperial (lbs/inches)
- Enter your weight and height
- Your BMI score and weight category are calculated instantly
- Compare your result to the BMI categories table above
BMI Calculator for Men vs Women
The standard BMI formula is the same for men and women. However, BMI does not account for differences in body composition — men typically have more muscle mass, and women typically have more body fat at the same BMI. For this reason, BMI is considered a screening tool, not a diagnostic measure. Always consult a healthcare professional for a full assessment.
Limitations of BMI
BMI is a useful starting point, but it has well-documented limitations according to the CDC’s BMI overview:
- Does not distinguish between muscle and fat mass
- May overestimate obesity in athletic individuals
- May underestimate body fat in older adults with low muscle mass
- Does not account for fat distribution (e.g., visceral vs subcutaneous fat)
- Different ethnic groups may have different health risks at the same BMI
FAQ — BMI Calculator
What is a healthy BMI for adults?
A BMI between 18.5 and 24.9 is considered a healthy weight range for most adults. However, this is a general guideline — individual health depends on many factors beyond BMI.
Is BMI accurate?
BMI is a useful screening tool but is not a direct measure of body fat or health. Athletes, pregnant women, the elderly, and growing children may get misleading BMI readings. Use it as one of several indicators.
What BMI is considered obese?
A BMI of 30.0 or higher is classified as obese according to the World Health Organization. Class I obesity is 30–34.9, Class II is 35–39.9, and Class III (severe obesity) is 40 or above.
How do I calculate BMI in pounds and inches?
Using the imperial formula: BMI = (weight in pounds ÷ height in inches²) × 703. For example, a person who is 5’9″ (69 inches) and weighs 160 lbs has a BMI of (160 ÷ 4761) × 703 = 23.6.
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