BMI Calculator
Calculate your Body Mass Index (BMI) from height and weight. See where you fall on the BMI scale.
Your BMI is 25.8, which falls in the "Overweight" category. BMI is a screening tool, not a diagnostic measure.
Why This Calculation Matters
The BMI Calculator turns a well-known health formula into an instant lookup. It's most useful when you're tracking a number over time or comparing yourself against published reference ranges from bodies like the CDC, NIH, or WHO. Use it as one data point among many, not a diagnosis.
How to Use This Calculator
- Enter your values in the input fields, each one has a label and help text explaining what to type.
- Results appear instantly as you type; there's no "calculate" button to press.
- Change any input to compare scenarios side by side.
All math happens in your browser. Nothing you type is sent to a server, saved, or shared.
Reading Your Result
A single number tells you less than a trend. Track this value over weeks or months rather than obsessing over day-to-day variation. Hydration, sleep, and timing can all shift short-term readings without reflecting any real change.
What Is BMI?
Body Mass Index (BMI) is a screening tool that estimates body fat based on height and weight. It's calculated as weight (kg) / height (m)².
BMI Categories
- Underweight: Below 18.5
- Normal weight: 18.5-24.9
- Overweight: 25-29.9
- Obesity: 30 and above
Limitations
BMI doesn't distinguish between muscle and fat. Athletes and muscular individuals may have a high BMI without excess body fat. Waist circumference and body fat percentage are complementary measures.
Formula
Metric: BMI = kg / m². Imperial: BMI = (lb / in²) × 703. WHO categories: underweight <18.5, normal 18.5-24.9, overweight 25-29.9, obese ≥30.
Worked Example
A 5'10" (178 cm), 170 lb (77 kg) adult.
- Weight
- 77 kg
- Height
- 178 cm
- Result
- 24.3 (Normal weight)
BMI between 18.5 and 24.9 is classified as normal weight per WHO thresholds.
When to Use This Calculator
- Track personal health metrics over time alongside guidance from your clinician.
- Understand how lifestyle changes may influence a given health number.
- Compare values against recognized reference ranges from CDC, NIH, or WHO.
Limitations & Common Mistakes
- Not a substitute for medical advice. Always consult a qualified clinician for anything that affects your care.
- Population-level formulas don't account for individual medical history, medications, or body composition nuances.
- Reference ranges evolve, use current CDC/NIH/WHO values when accuracy matters.
Frequently Asked Questions
Is BMI accurate?
BMI is a useful screening tool but has limitations. It doesn't distinguish between muscle and fat mass, doesn't account for body composition, and may not be accurate for athletes, elderly, or certain ethnic groups. Use it as one data point alongside waist circumference and other health indicators.
What is a healthy BMI?
The NIH and WHO classify a BMI of 18.5-24.9 as "normal weight." However, health depends on many factors beyond BMI including fitness level, waist circumference, blood pressure, blood sugar, and cholesterol levels.
Should I use the BMI Calculator for medical decisions?
No. This tool is educational. For anything affecting your health or treatment, consult a qualified clinician who can factor in your full medical history.
Which reference values does this use?
Where relevant, thresholds match CDC, NIH, or WHO guidance. Sources are linked in the "Sources & Further Reading" section below.
Is this calculator free to use?
Yes. The BMI Calculator is free, requires no signup, and runs entirely in your browser, your inputs are never sent to a server.
Related Calculators
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Calorie Intake Calculator
Calculate how many calories you should eat daily based on your goals, lose, maintain, or gain weight.
BMI Calculator for Children
Calculate BMI for children and teens (ages 2-20) using CDC growth charts and age-based percentiles.
Related guides
- TDEE: The Only Calorie Number That Actually Drives Weight ChangeBMR tells you the baseline. Calorie intake tells you the input. TDEE is the number that decides whether you lose, maintain, or gain, and it is the one most people miscalculate.
- BMI vs. Body Fat Percentage: Which Number Actually Measures HealthBMI is free and fast. Body fat percentage is more accurate. Waist-to-hip ratio predicts cardiovascular risk better than either. Here is when to use which, and what the CDC and WHO actually recommend.