Overview
Calculate Body Mass Index from metric or imperial measurements, with the standard adult classification shown alongside the score. Switch between kilograms/centimetres and pounds/feet+inches with one toggle; the result updates as you type and the calculation runs in your browser. BMI is a population screening measure, and this page treats it that way rather than as a diagnosis.
How It Works
Pick Metric (kg/cm) or Imperial (lb/ft+in) at the top. In metric mode enter weight in kilograms and height in centimetres; in imperial mode enter weight in pounds and height as feet plus inches in two fields. The result card shows the BMI score to one decimal place and its classification immediately: Underweight below 18.5, Normal weight from 18.5 to 24.9, Overweight from 25 to 29.9, and Obese at 30 or above. Beneath the score, the card lists all four WHO adult categories with their boundaries and highlights the one you fall in.
Step-by-Step Usage Guide
- Pick Metric or Imperial; both produce the same score for the same person.
- Enter weight, and height either in centimetres or as feet plus inches.
- Read the BMI score, its classification, and the category table in the result card.
- Treat the number as a screening signal; discuss it with a healthcare professional.
Technical Specifications & Standards
The formula is the standard Quetelet index: weight in kilograms divided by the square of height in metres. Imperial input is converted exactly before the formula runs - pounds by the defined factor 0.45359237 kilograms per pound, feet and inches to metres at 0.0254 metres per inch - so a person's BMI is identical whichever unit system they type, and the two paths are tested against each other. Non-positive or invalid inputs are guarded and produce a dash rather than a division error. The classification thresholds - 18.5, 25 and 30 - are the World Health Organization's adult cut-offs, the same points the CDC's adult calculator applies. What BMI cannot see is at least as important as what it computes: it does not distinguish muscle from fat, so athletes with high lean mass routinely score as overweight; it says nothing about fat distribution, which is why waist measures matter; and the thresholds were calibrated on adult populations, so they are not valid for children, who use age-and-sex percentile charts, or in a straightforward way during pregnancy. The page carries a standing notice to this effect: BMI is a screening measure, not a diagnosis, and not medical advice.
Targeted Use Cases
- A quick self-check against the standard adult bands before a health review.
- Tracking a weight-management programme's direction over weeks.
- Fitness onboarding forms that record a baseline BMI from clients who measure in pounds and feet.
- Understanding why a muscular training partner scores in the overweight band.
Notes & Gotchas
- Measure height without shoes and weight at a consistent time of day.
- Read the category alongside waist circumference, not in isolation.
- Do not use adult thresholds for children or teenagers - they need percentile charts.
- Take a high score with muscle mass as a prompt for body-composition measures, not alarm.
Frequently Asked Questions
Does the calculator accept pounds and inches?
Yes. Toggle to Imperial and enter pounds and feet plus inches; the tool converts to exact metric factors (0.45359237 kg per pound, 0.0254 m per inch) before computing, so the score matches the metric path to full precision.
Is BMI accurate for athletes?
Often not. BMI does not distinguish muscle from fat, so people with high lean mass can score as overweight despite low body fat. Waist measurement or body-composition testing is more informative for them.
Is this medical advice?
No. BMI is a population screening measure, and the page says so. A clinician interpreting it alongside other measurements is the only sound basis for health decisions.
What are the category boundaries?
Underweight below 18.5, normal weight 18.5 to 24.9, overweight 25 to 29.9, obese 30 and above - the WHO adult cut-offs, also used by the CDC's adult calculator.