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BMI Calculator – Calculate Your Body Mass Index Online

BMI Calculator

The BMI Calculator (Body Mass Index) is a simple, free online tool that estimates your body fat based on height and weight. Use this bmi calculator to quickly determine your BMI, see your weight category (underweight, normal, overweight, obese), and find your healthy weight range. It is an excellent weight calculator and healthy weight calculator for adults. Whether you want to calculate bmi for fitness tracking, medical screening, or personal health goals, this bmi checker provides accurate results with a clear step‑by‑step explanation. The included bmi chart helps you visualise where you fall on the scale.

BMI Scale18.5253040+Underweight | Normal | Overweight | ObeseBMI = weight (kg) ÷ height² (m)Healthy range: 18.5 – 24.9

BMI Formula & Classification

Metric: BMI = weight (kg) ÷ height² (m²)

Imperial: BMI = weight (lb) ÷ height² (in²) × 703

Categories: Underweight (<18.5) | Normal (18.5–24.9) | Overweight (25–29.9) | Obese (≥30)

How to Use This BMI Calculator

  1. Choose Metric (kg/cm) or Imperial (lb, ft/in).
  2. Enter your weight and height.
  3. Click “Calculate BMI”.
  4. View your BMI, category, and healthy weight range.
Limitations of BMI

BMI does not directly measure body fat percentage. It may overestimate body fat in muscular individuals (athletes) and underestimate in older adults who have lost muscle mass. For children and teens, BMI is age‑ and sex‑specific (percentile charts). Always consult a healthcare provider for a complete health evaluation.

WHO Body Mass Index (BMI) Categories & Health Risk Table

Weight CategoryBMI Range (kg/m²)BMI Prime RatioAssociated Health Risk Level
Underweight< 18.5< 0.74Nutritional deficiency & osteopenia risk
Normal Weight18.5 – 24.90.74 – 1.00Lowest risk for chronic metabolic disease
Overweight25.0 – 29.91.00 – 1.20Increased cardiovascular & diabetes risk
Obese Class I (Moderate)30.0 – 34.91.20 – 1.40High metabolic & joint disease risk
Obese Class II (Severe)35.0 – 39.91.40 – 1.60Very high cardiovascular risk
Obese Class III (Morbid)≥ 40.0≥ 1.60Extremely high severe mortality risk

Why Use a BMI Calculator?

This body mass index calculator is based on WHO standards. Use it as a reliable bmi checker and healthy weight calculator. Share it with friends and family to help them understand their BMI.

Frequently Asked Questions About BMI

  • What is a healthy BMI for adults? Between 18.5 and 24.9.
  • Is BMI the same for men and women? Yes, the same formula applies to adults of both sexes, but body fat distribution differs.
  • Can I use this calculator for children? No, children use BMI‑for‑age percentiles. Use a specialised paediatric calculator.
  • How often should I check my BMI? Once a month or as recommended by your doctor.

How to Achieve a Healthy BMI

If your BMI is outside the normal range, small lifestyle changes can help. For overweight or obesity, focus on balanced nutrition, portion control, and regular exercise. For underweight, increase calorie intake with nutrient‑dense foods and strength training. Use this BMI calculator to track your progress over time.

Bookmark this bmi calculator to use it as your go‑to body mass index calculator, weight calculator, and healthy weight calculator.

Step‑by‑Step Manual Example

Metric: Weight = 70 kg, Height = 1.70 m (170 cm)

BMI = 70 / (1.70 × 1.70) = 70 / 2.89 = 24.22 → Normal weight

Healthy weight range: 18.5 × 2.89 = 53.5 kg to 24.9 × 2.89 = 72.0 kg

Frequently Asked Questions about BMI

What is Body Mass Index (BMI)?
Body Mass Index (BMI) is a standardized screening metric that compares your weight to your height squared. It classifies individuals into underweight, normal weight, overweight, or obese categories.
How is BMI calculated?
Metric: BMI = weight (kg) / height² (m²). Imperial: BMI = [weight (lbs) / height² (in²)] × 703. Our calculator supports both measurement systems automatically.
What is a normal healthy BMI range?
According to the World Health Organization (WHO), a healthy adult BMI ranges from 18.5 to 24.9 kg/m².
How is ideal healthy weight calculated from BMI?
Healthy weight range is calculated by multiplying 18.5 and 24.9 by your height in meters squared: Min Weight = 18.5 × h², Max Weight = 24.9 × h².
Is BMI accurate for athletes and bodybuilders?
BMI can overestimate body fatness in athletes with dense muscle mass, as muscle weighs more than fat. It should be combined with body fat percentage or waist circumference.
Is BMI accurate for older adults?
In older adults, age-related muscle loss (sarcopenia) may cause BMI to underestimate body fat. A slightly higher BMI (23–27) is often considered protective in elderly populations.
What is BMI Prime?
BMI Prime is the ratio of a person's actual BMI to the upper limit of normal BMI (25). A BMI Prime under 0.74 is underweight, 0.74–1.00 is normal, and over 1.00 is overweight.
Can this BMI calculator be used for children and teenagers?
No. Children and teens aged 2–19 must use CDC BMI-for-age percentile growth charts, which account for age and biological sex development.