Free BMI Calculator
Calculate your Body Mass Index (BMI) instantly with our free online BMI calculator. Supports imperial and metric units. See your BMI category and what it means for your health.
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Your BMI
24.4
Category
Normal weight
BMI Categories:
Underweight: Below 18.5 · Normal: 18.5–24.9 · Overweight: 25–29.9 · Obese: 30+
BMI is a screening tool and does not directly assess body fat or health. Consult a healthcare provider for medical advice.
Formula
BMI = weight (kg) / height (m)² — or BMI = (weight (lbs) × 703) / height (in)²What Is BMI and How Is It Calculated?
Body Mass Index (BMI) is a simple numerical value calculated from your height and weight. Developed by Belgian mathematician Adolphe Quetelet in the 1830s, BMI has become one of the most widely used screening tools for categorizing weight status. The formula divides your weight by the square of your height, producing a number that falls into one of four main categories: underweight, normal weight, overweight, or obese.
For imperial measurements, the formula multiplies your weight in pounds by 703, then divides by height in inches squared. For metric, it's simply your weight in kilograms divided by your height in meters squared. Our calculator handles both systems automatically.
Understanding BMI Categories
The World Health Organization (WHO) defines four primary BMI categories for adults:
- Underweight (below 18.5) — may indicate malnutrition, eating disorders, or other health conditions
- Normal weight (18.5–24.9) — generally associated with the lowest health risks
- Overweight (25–29.9) — may increase risk of cardiovascular disease and type 2 diabetes
- Obese (30 and above) — significantly higher risk of various health conditions
Limitations of BMI
While BMI is a useful starting point, it has well-documented limitations. It cannot distinguish between muscle mass and body fat — a muscular athlete may be classified as 'overweight' despite having very low body fat. Similarly, older adults who have lost muscle mass might have a 'normal' BMI despite carrying excess fat.
BMI also doesn't account for fat distribution. Research shows that where you carry fat matters: visceral fat around the abdomen poses greater health risks than subcutaneous fat elsewhere. For a more complete picture, consider using our Body Fat Calculator alongside BMI.
Tips for Maintaining a Healthy BMI
- Focus on whole foods — fruits, vegetables, lean proteins, and whole grains support healthy weight management
- Stay active — aim for at least 150 minutes of moderate exercise per week
- Monitor portions — even healthy foods can contribute to weight gain in excess
- Get adequate sleep — poor sleep is linked to weight gain and metabolic disruption
- Track your progress — regular measurements help you stay accountable
Frequently Asked Questions
What is a healthy BMI range?
A healthy BMI falls between 18.5 and 24.9, classified as 'normal weight.' However, BMI is just one indicator of health. Athletes with high muscle mass may have a higher BMI but still be very healthy. Always consider BMI alongside other measurements like body fat percentage and waist circumference.
How accurate is BMI as a health indicator?
BMI is a useful screening tool but has limitations. It doesn't distinguish between muscle and fat, doesn't account for bone density, and may be less accurate for athletes, elderly individuals, and pregnant women. It's best used as a starting point alongside other health metrics.
How is BMI calculated differently for children?
For children and teens (ages 2-20), BMI is calculated the same way but interpreted using age- and sex-specific percentiles. A child's BMI is compared to other children of the same age and sex because body composition changes as they grow.
Can you have a normal BMI but still be unhealthy?
Yes, this is sometimes called 'normal weight obesity.' You can have a BMI in the normal range but carry excess body fat, especially around the midsection. This visceral fat is linked to higher risks of heart disease and diabetes, which is why body fat percentage is an important complementary measurement.
How often should I check my BMI?
Checking your BMI once every few months is sufficient for most adults. More important than any single reading is the trend over time. If you're actively trying to lose or gain weight, monthly check-ins can help track progress, but daily fluctuations in weight are normal and not cause for concern.