BMI Calculator — Find Out Your Body Mass Index Online

Use our free online BMI calculator to quickly find out your body mass index and your weight category (Underweight, Normal, Overweight, Obesity I–III). There is no download and no signup required — the calculation runs instantly in your browser.

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What is BMI?

Body Mass Index (BMI) is a simple screening measure that relates your weight to your height. It is widely used to classify weight status and give a quick indication of potential health risks associated with being underweight or overweight.

BMI is calculated by the formula:

• Metric: BMI = weight (kg) / height (m)^2
• Imperial: BMI = weight (lb) × 703 / height (in)^2

While BMI does not measure body fat directly, it helps identify general weight ranges and is recognized in public health guidelines, including WHO classifications.

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How to use the BMI calculator

1. Select units: choose metric (cm, kg) or imperial (ft/in, lbs).
2. Enter height: either in centimeters or feet and inches.
3. Enter weight: either in kilograms or pounds.
4. Click Calculate to see your BMI and category instantly.

You can switch units at any time — the tool supports both metric and imperial measurements.

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BMI categories (WHO)

• Underweight: BMI < 18.5
• Normal: 18.5 ≤ BMI < 25
• Overweight: 25 ≤ BMI < 30
• Obesity I: 30 ≤ BMI < 35
• Obesity II: 35 ≤ BMI < 40
• Obesity III: BMI ≥ 40

The calculator also shows an ideal weight range for your height based on the Normal BMI interval 18.5–24.9, both in kg and lbs.

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Why use an online BMI calculator?

• Fast and free: no cost, no ads, no email required.
• Mobile-friendly: works on phones, tablets, and desktops.
• Privacy-first: calculations run locally; nothing is sent to servers.
• Clear output: numeric BMI plus category and ideal range.
• Helpful for tracking: quick check when monitoring weight changes.

If you are planning health goals, pairing BMI with waist circumference, activity level, and nutrition quality creates a more complete picture.

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Interpreting your results

• Underweight: may indicate insufficient energy intake or a medical condition. Consider increasing nutrient-dense foods and consulting a professional if unintentional.
• Normal: generally associated with lower risk; maintain balanced habits and regular activity.
• Overweight: elevated risk of cardiovascular and metabolic issues over the long term; gradual lifestyle adjustments can help.
• Obesity I–III: higher health risks; talk to a clinician for a personalized plan.

BMI is a screening tool, not a diagnosis. Individual health varies with genetics, age, muscle mass, and distribution of fat. For athletes and muscular individuals, BMI can overestimate fatness.

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Common questions

Is the BMI calculator accurate?
BMI uses height and weight only, so it is approximate. It is useful for population-level screening but less precise for individuals with high muscle mass or unique body composition.

Can I use imperial measurements?
Yes. Choose ft/in for height and lbs for weight. The tool automatically applies the correct formula.

What is an ideal BMI?
There is no single “ideal” for everyone, but the Normal category (18.5–24.9) is commonly referenced. Our calculator also shows the corresponding ideal weight range for your height.

Should I rely only on BMI?
No. Combine BMI with waist measurement, physical activity, diet quality, and where possible body fat percentage for a fuller picture.

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Tips for healthy change

• Focus on gradual adjustments: small weekly changes compound.
• Prioritize whole foods, adequate protein, fruits, and vegetables.
• Aim for regular movement: walking, resistance training, and activities you enjoy.
• Track habit consistency more than scale fluctuations.

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Conclusion

Looking for a free online BMI calculator? Use this tool to find out your body mass index, check if you are underweight, normal, overweight, or obese, and see your ideal weight range. It works instantly with no download and no signup.

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