BMI Calculator

What Is BMI?

BMI(Body Mass Index) is a number calculated from your height and weight that gives a rough indication of whether your weight is in a healthy range. It's the most widely used screening tool for weight categories: underweight, healthy weight, overweight, and obese. The standard was developed in the 1830s by Belgian mathematician Adolphe Quetelet and adopted by the World Health Organization for population-level health statistics.

The BMI Formula

The calculation is simple:

• Metric: BMI = weight (kg) ÷ height² (m²)
• Imperial: BMI = (weight (lb) ÷ height² (in²)) × 703

For example, someone who is 170 cm and 65 kg: 65 ÷ (1.70 × 1.70) = 22.5, placing them in the healthy weight range.

BMI Categories (WHO Standard)

• Below 18.5: Underweight
• 18.5 – 24.9: Healthy weight
• 25.0 – 29.9: Overweight
• 30.0 – 34.9: Obese (Class I)
• 35.0 – 39.9: Obese (Class II)
• 40.0 and above: Obese (Class III)

What BMI Doesn't Tell You

BMI is a useful screening tool, but it has real limitations. It measures total weight relative to height, but it cannot tell the difference between fat, muscle, bone, and water. This matters:

• Athletes and bodybuildersoften score "overweight" because muscle is denser than fat. A professional rugby player with 10% body fat might have a BMI of 28.
• Older adultsmay have a "healthy" BMI but high body fat and low muscle mass — a risk that BMI misses.
• Body fat distributionmatters. Fat around the waist carries more health risk than fat around the hips, but BMI can't tell the difference.
• Children and teens need percentile-based charts, not the adult ranges.

Healthy Weight Range for Your Height

This calculator also shows the weight range that corresponds to a BMI of 18.5–24.9 for your height. If your current weight falls within this range, your BMI is in the healthy category. If you're above or below, the range gives you a concrete target.

Alternatives to BMI

For a more complete picture of health, consider these complementary measurements:

• Waist circumference. Over 40 inches (102 cm) for men or 35 inches (88 cm) for women indicates higher metabolic risk.
• Waist-to-hip ratio. Compares waist and hip measurements to assess fat distribution.
• Body fat percentage. Measured with calipers, scales, or DEXA scans. Provides what BMI cannot.

Frequently Asked Questions

Is BMI accurate for everyone?

No. BMI works reasonably for the average sedentary adult but overestimates body fat in muscular people and underestimates it in older adults who have lost muscle. Use it as a starting point, not the final word.

What is a healthy BMI for me?

For most adults aged 20-65, a BMI between 18.5 and 24.9 is considered healthy. People over 65 may benefit from a slightly higher BMI (25-27), as some extra weight can be protective in older age. Consult your doctor for personalized guidance.

Should I use BMI to set weight loss goals?

BMI is a useful reference point, but better goals focus on body fat percentage, waist measurement, fitness level, and how you feel. A 5-10% weight loss can significantly improve health markers even if your BMI doesn't cross a category line.