BMI Calculator
Body Mass Index from height and weight with WHO clinical classification bands.
Understanding this tool
Why nurses use it
Body Mass Index is a quick screening measure used on admission, in nutrition assessment, and as context for weight-based protocols. It helps nurses communicate nutritional status using a standard WHO classification.
When to use it
Use for adult screening and documentation — not as a sole measure of health or body composition. Paediatric BMI uses growth charts instead.
Calculate
How to use this calculator
- Measure or obtain weight and height (use unit selectors if needed).
- Calculate BMI and note the WHO category.
- Document and escalate nutrition concerns per local pathway.
How the calculation works
BMI = weight (kg) ÷ height (m)². Height is converted to metres before squaring. Categories: underweight <18.5, normal 18.5–24.9, overweight 25–29.9, obese ≥30.
Formula used by this tool — verify units before applying at the bedside.
Worked example
Limitations & clinical notes
- WHO categories are for adults; not validated for children or athletes.
- Does not measure body composition.
References
Key sources: WHO — Body mass index classification.
Don’t miss new nursing tools
Subscribe for alerts when we add calculators, clinical scores, and reference updates to NurseOnShift.
Disclaimer: This calculator is for educational and bedside double-check purposes only. It does not replace institutional protocols, prescriber orders, pharmacist verification, or clinical judgment. Always follow your local policies — especially for high-risk medications, infusions, pediatrics, and critical care. If the patient is acutely unwell, escalate immediately rather than relying on any calculator output.