ƒCalculatorFree
Fitness & Health

BMI Calculator

Calculate your Body Mass Index (BMI) using metric or imperial units. Get your weight category and healthy weight range.

Calculation Inputs

Results computed instantly — your data never leaves your device.

Live Results

Real-Time

BMI

24.2

Category

Normal weight

Healthy Range

53.5 kg - 72 kg

100% Client-SidePrivate & Secure

Recommendation

Congratulations! You are maintaining a healthy body weight. Keep up the balanced diet and regular physical activity.

BMI Scale

< 18.5

Underweight

18.5 – 24.9

Normal

25.0 – 29.9

Overweight

≥ 30.0

Obese

How to Use the BMI Calculator

  1. 1

    Select your unit system: Metric (kg/cm) or Imperial (lbs/inches).

  2. 2

    Enter your weight in the weight field.

  3. 3

    Enter your height in the height field.

  4. 4

    Your BMI score, weight category, and healthy weight range appear immediately.

Formula & Mathematical Basis

BMI = weight (kg) ÷ height² (m²) | Imperial: BMI = 703 × weight (lbs) ÷ height² (in²)

Variable Key

BMI

Body Mass Index — dimensionless ratio of weight to squared height

weight

Body mass in kilograms (metric) or pounds (imperial)

height

Stature in metres (metric) or inches (imperial)

703

Unit-conversion factor for the imperial formula (kg/m² → lbs/in²)

📝 The WHO and CDC classify BMI into four ranges: Underweight (<18.5), Normal weight (18.5–24.9), Overweight (25–29.9), and Obese (≥30). Extended classifications divide Obesity into Class I (30–34.9), Class II (35–39.9), and Class III (≥40).

Step-by-Step Examples

1

Metric calculation — average adult male

Scenario: Weight: 80 kg, Height: 1.80 m

  1. 1.Square the height: 1.80² = 3.24 m².
  2. 2.Divide weight by squared height: 80 ÷ 3.24 = 24.69.
  3. 3.Compare to WHO ranges: 24.69 falls within 18.5–24.9.
✅ BMI = 24.7 → Normal weight. Healthy range for this height: 60–80.9 kg.
2

Imperial calculation — female athlete

Scenario: Weight: 150 lbs, Height: 65 inches (5′5″)

  1. 1.Square height in inches: 65² = 4,225.
  2. 2.Apply factor: 703 × 150 ÷ 4,225 = 24.96.
  3. 3.Note: despite being muscular, BMI classifies as Normal weight.
✅ BMI = 25.0 → Borderline Normal/Overweight. Muscle mass is not distinguished.

Practical Use Cases

  • Population-level obesity screening and public health research
  • Clinical triage — initial assessment before detailed body-composition testing
  • Life and health insurance underwriting (risk stratification)
  • Paediatric growth monitoring (using age- and sex-specific BMI-for-age percentiles)
  • Bariatric surgery candidacy assessment (BMI ≥ 35 threshold)
  • Occupational health checks for physically demanding roles

Common Mistakes to Avoid

  • Treating BMI as a direct measure of body fat — it measures relative weight, not composition.
  • Using the metric formula with imperial measurements (or vice versa) without converting units first.
  • Applying adult BMI ranges to children — use WHO/CDC BMI-for-age growth charts instead.
  • Ignoring other risk factors such as waist circumference, blood pressure, and cholesterol.
  • Athletes with high muscle mass may show "Overweight" BMI despite low body-fat percentage.

Glossary of Terms

BMI (Body Mass Index)
A numerical index derived from height and weight, used as a proxy for body fat and obesity risk at the population level.
Obesity
A chronic condition defined by the WHO as BMI ≥ 30, associated with increased risk of type 2 diabetes, cardiovascular disease, and certain cancers.
Waist-to-Height Ratio
An alternative adiposity index (waist ÷ height) that some studies show correlates more strongly with metabolic risk than BMI.
Body Fat Percentage
The proportion of total body mass that is fat tissue, measured via DEXA, hydrostatic weighing, or bioelectrical impedance.

Frequently Asked Questions

What is a healthy BMI?

▾
A BMI between 18.5 and 24.9 is considered healthy for most adults. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese.

How is BMI calculated?

▾
BMI = weight (kg) ÷ height² (m). For imperial units: BMI = 703 × weight (lbs) ÷ height² (inches). Our calculator handles both unit systems automatically.

Is BMI accurate for everyone?

▾
BMI is a useful screening tool but has limitations. It may overestimate body fat in athletes with high muscle mass and underestimate it in older adults. Consult a healthcare professional for a complete assessment.

What is my ideal weight according to BMI?

▾
The calculator shows your healthy weight range based on your height. This is the weight range where BMI falls between 18.5 and 24.9.

Sources & References

  1. [1]
    Body Mass Index — Obesity— World Health Organization (WHO), 2024
  2. [2]
    About Adult BMI— Centers for Disease Control and Prevention (CDC), 2023
  3. [3]
    Keys et al. — Indices of Relative Weight and Obesity— Journal of Chronic Diseases, 1972

CalculatorFree Health TeamPublic Health & Clinical Nutrition Review

Content reviewed against WHO obesity classification guidelines and CDC clinical guidance.

Related Calculators

Calorie Calculator

Calculate your daily calorie needs using the Mifflin-St Jeor formula. Find your BMR and TDEE for weight loss or gain.

Fitness & Health

Mortgage Calculator

Calculate your monthly mortgage payment including principal, interest, taxes, and insurance (PITI). See the full amortization schedule.

Financial

Mortgage Amortization Calculator

View the complete amortization schedule for any mortgage. See exactly how each payment is split between principal and interest, year by year.

Financial

House Affordability Calculator

Find out how much house you can afford based on your income, debts, and down payment. Uses the 28/36 DTI rule used by mortgage lenders.

Financial

Rent Calculator

Calculate your true total cost of renting including utilities, insurance, parking, and fees. See 10-year projections with annual rent increases.

Financial

Rent vs. Buy Calculator

Compare the true financial cost of renting versus buying a home over time. Find your break-even year and net cost difference.

Financial