BMI Calculator – Body Mass Index, Category & Healthy Weight Range (Free Online)

BMI Calculator – Body Mass Index, Category & Healthy Weight Range

Use this free BMI Calculator to compute your Body Mass Index from height and weight in metric or imperial units. See your adult BMI category (WHO), BMI Prime, and the healthy weight range for your height. Everything runs in your browser—no data saved.

Contents: BMI Calculator • How It Works • Adult BMI Categories • FAQ

BMI Calculator

Units Metric (kg, cm) Imperial (lb, ft/in)

Weight (kg)

Height (cm)

Weight (lb)

Height (ft / in)

Auto-calc while typing

Your BMI

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BMI Prime

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BMI ÷ 25 (healthy upper bound)

Healthy Weight Range

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for BMI 18.5–24.9

Disclaimer: BMI is a general screening tool for adults and does not replace medical advice. It may not reflect body composition for athletes, pregnant people, or certain conditions.

How This BMI Calculator Works

• For metric: BMI = weight (kg) ÷ [height (m)]².
• For imperial inputs: values are converted to kg/cm, then the same formula is used.
• BMI Prime = BMI ÷ 25 (the upper bound of the “normal” range). Prime < 1 means below 25; > 1 means above.
• Healthy weight range is computed from BMI 18.5–24.9 for your height.

Adult BMI Categories (WHO)

Category	BMI (kg/m²)
Underweight	< 18.5
Normal weight	18.5–24.9
Overweight	25.0–29.9
Obesity	≥ 30.0

FAQ – BMI Calculator

What inputs do I need?

Just enter your height and weight (in metric or imperial). The calculator converts and computes BMI automatically.

Do I need to fast or measure at a certain time?

No. BMI uses your current height and weight only.

Why is my category different from other sites?

Some regions use extra sub-classes (e.g., Class I/II/III obesity) or population-specific cutoffs. This tool uses standard WHO adult ranges.