Free Body Mass Index Calculator
BMI Calc Now is a free online Body Mass Index calculator that computes your BMI from weight and height using the WHO formula (BMI = kg/m²). It displays your BMI value, WHO classification with color coding, a visual gauge, healthy weight range, BMI Prime, and Ponderal Index. Available in 20 languages with metric and imperial units — no sign-up required and no data collected.
Calculate your BMI instantly — no sign-up, no data collected, available in 20 languages.
How to Use This Calculator
Choose your unit system
Toggle between Metric (kg/cm) and Imperial (lbs/ft-in). All labels update automatically.
Enter your weight
Type your weight in kilograms or pounds. The calculator accepts values from 1 to 500 kg (or 1 to 1,100 lbs).
Enter your height
For Metric, enter your height in centimeters. For Imperial, enter feet and inches separately. The calculator accepts heights from 1 to 300 cm (or 1 to 120 inches).
View your results
Your BMI is calculated instantly. You will see your BMI value, WHO category with color coding, a visual gauge, your healthy weight range, BMI Prime, and Ponderal Index.
Copy or share your result
Click the copy button to save your BMI result to your clipboard. Share it with your healthcare provider or keep it for your personal records.
What Is BMI?
Body Mass Index, or BMI, is a numerical value calculated from your weight and height. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and is now used worldwide as a quick screening tool to categorize individuals into weight status categories.
The formula is straightforward: BMI equals your weight in kilograms divided by your height in meters squared (BMI = kg / m²). For imperial units, the formula is weight in pounds multiplied by 703, divided by height in inches squared.
The World Health Organization uses BMI to classify adults into categories ranging from Severe Thinness (below 16) to Obese Class III (40 and above). A BMI between 18.5 and 24.9 is considered normal weight. While BMI is a useful starting point, it does not distinguish between muscle and fat mass, and should be considered alongside other health assessments.
BMI = weight (kg) / height² (m²)
BMI Classification Table (WHO)
| Classification | BMI Range (kg/m²) | Example Weight (5'9") |
|---|---|---|
| Severe Thinness | < 16 | < 108 lbs(< 49 kg) |
| Moderate Thinness | 16 – 17 | 108 – 115 lbs(49 – 52 kg) |
| Mild Thinness | 17 – 18.5 | 115 – 125 lbs(52 – 57 kg) |
| Normal | 18.5 – 25 | 125 – 169 lbs(57 – 77 kg) |
| Overweight | 25 – 30 | 169 – 203 lbs(77 – 92 kg) |
| Obese Class I | 30 – 35 | 203 – 236 lbs(92 – 107 kg) |
| Obese Class II | 35 – 40 | 236 – 270 lbs(107 – 123 kg) |
| Obese Class III | > 40 | > 270 lbs(> 123 kg) |
* Example weights shown for a person 5'9" (175 cm) tall
Health Risks Associated with BMI
Risks of Being Overweight
A BMI above 25 is associated with increased risk of several serious conditions, according to the Centers for Disease Control and Prevention (CDC):
- High blood pressure (hypertension)
- Elevated LDL cholesterol and triglycerides, lower HDL cholesterol
- Type 2 diabetes
- Coronary heart disease and stroke
- Gallbladder disease
- Osteoarthritis and joint deterioration
- Sleep apnea and breathing problems
- Certain cancers (breast, colon, kidney, liver, endometrial)
- Clinical depression and anxiety
- Reduced quality of life and increased mortality risk
Risks of Being Underweight
A BMI below 18.5 also carries health risks that should not be overlooked:
- Malnutrition and vitamin deficiencies
- Anemia (reduced ability to transport oxygen)
- Osteoporosis and increased fracture risk
- Weakened immune system
- Growth and development issues in younger adults
- Hormonal imbalances and reproductive issues
- Increased surgical complication risk
- Higher overall mortality risk
If your BMI falls outside the 18.5–25 range, consider consulting a healthcare professional. BMI is a screening tool — not a diagnosis.
Limitations of BMI
BMI is a useful screening tool, but it has important limitations. Because the formula uses only weight and height, it cannot distinguish between muscle mass, bone density, and body fat. This means BMI may overestimate body fat in athletes and muscular individuals, and underestimate it in older adults who have lost muscle mass.
BMI is also influenced by factors it does not measure, including age, sex, ethnicity, and fat distribution. For example, older adults tend to carry more body fat than younger adults at the same BMI. Women typically have more body fat than men at equivalent BMI values. And certain ethnic groups — particularly South Asian and East Asian populations — may face higher health risks at lower BMI thresholds.
Despite these limitations, BMI remains a reliable indicator of body fat for roughly 90–95% of the general population. For the most complete picture, use BMI alongside waist circumference, body fat percentage, and clinical assessments from a qualified healthcare professional.