BMI Calculator
A simple, accurate way to check if you're at a healthy weight. Enter your height and weight below.
About Body Mass Index (BMI)
Body Mass Index (BMI) is the most widely used screening tool for weight category. Developed by Adolphe Quetelet in the 19th century, it provides a quick numerical estimate of a person's 'thickness' or 'thinness', allowing health professionals to discuss weight problems more objectively.
How to Use This Calculator
Step-by-Step
- 1Select your preferred Unit System: 'US Units' (Pounds/Feet/Inches) or 'Metric Units' (Kilograms/Centimeters).
- 2Enter your Height. Stand tall against a wall without shoes for the most accurate measurement.
- 3Enter your Weight. Use a digital scale in the morning for consistency.
- 4Your BMI will be calculated automatically. Compare your number to the WHO categories below.
Pro Tips
- ✓Use the slider or input fields for precise entry.
- ✓Measure yourself in the morning before eating for the most consistent weight tracking.
- ✓If you are very muscular, consider using our Body Fat Calculator instead, as BMI may overestimate your fat.
The Math Behind It
The formula for BMI is remarkably simple. It represents your weight divided by your height squared.
Metric Formula
BMI = kg / m²Weight in Kilograms divided by Height in Meters squared.
Imperial Formula
BMI = 703 × lbs / in²Weight in Pounds divided by Height in Inches squared, multiplied by a conversion factor of 703.
Interpretation (WHO Standards)
Underweight
< 18.5
Normal
18.5 - 24.9
Overweight
25 - 29.9
Obese
30+
Real World Applications
Medical Screening
Doctors use BMI as a "vital sign" alongside blood pressure and pulse. A high BMI triggers further testing for diabetes (HbA1c), cholesterol, and hypertension. It's the first step in preventative health care.
Life Insurance
Insurance companies use BMI to calculate premiums. Applicants with a BMI in the "Obese" range may pay 25-50% more for coverage because statistically, they are at higher risk for chronic illness.
Fitness Tracking
While not perfect for bodybuilders, BMI is great for the general population tracking weight loss. Dropping from a BMI of 31 (Obese) to 29 (Overweight) significantly reduces the risk of heart disease and stroke.
Frequently Asked Questions
Is BMI accurate for athletes?
BMI is often inaccurate for athletes or bodybuilders because it does not distinguish between muscle mass and fat mass. A bodybuilder with low body fat may have a 'Obese' BMI simply due to weight. In these cases, Body Fat Percentage is a better metric.
Does BMI change with age?
The calculation itself (kg/m²) remains the same, but the *interpretation* changes for children and teens (percentiles are used). For older adults (65+), slightly higher BMI ranges (25-27) are often considered healthy to protect against frailty.
What is the difference between BMI and Body Fat Percentage?
BMI is a height-to-weight ratio. Body Fat Percentage is the percent of your total weight that comes from fat tissue. Body Fat is a more precise health indicator but requires special tools (calipers, DEXA scans) to measure, whereas BMI only requires a scale and tape measure.
Why is waist circumference important?
Waist circumference measures abdominal obesity (visceral fat), which is more dangerous than subcutaneous fat (fat under the skin). If your BMI is normal but you have a large waist measurement (>40in for men, >35in for women), you may still be at risk for heart disease.
How can I lower my BMI?
To lower your BMI, you need to lower your weight. The most effective method is a combination of a calorie-controlled diet (eating less than your TDEE) and increased physical activity. Aim for a sustainable loss of 1-2 lbs per week.