BMI Calculator
find your Body Mass Index instantly
Calculate your Body Mass Index (BMI) from your height and weight, with the formula and category shown clearly. Free, unlimited, no sign-up needed.
Enter your height and weight
BMI Categories (WHO Standard, Adults)
These are the standard WHO adult ranges. BMI for children and teenagers (under 18) is age- and gender-specific and should be checked against growth charts, not this adult scale — talk to a doctor for a proper reading.
Free Online BMI Calculator for Students
This free BMI calculator instantly finds your Body Mass Index from your height and weight, in either metric (kg/cm) or imperial (lb/ft-in) units — with the exact formula and category shown, not just a number. It's useful for Biology and Physical Education coursework, health awareness projects, or simply checking your own numbers.
BMI is calculated as weight in kilograms divided by height in metres squared (BMI = kg ÷ m²). It's a simple screening tool, not a diagnosis — it doesn't account for muscle mass, bone density, age, or body composition, so two people with the same BMI can have very different body types.
If you're studying BMI, nutrition, or human physiology for Biology homework, StudyHelpAI's free AI tutor can explain the underlying concepts — like why BMI is used as a population-level screening tool and where it falls short for individuals — step by step in English or Tamil.
← Back to Biology Homework HelpBMI Calculator — Questions Answered
Yes — it's completely free with no sign-up, no daily limit, and no ads. It runs entirely in your browser, so results are instant.
BMI = weight (kg) ÷ height (m)². For imperial units, weight in pounds and height in inches are first converted to kilograms and metres before the same formula is applied, so results match exactly either way.
No — BMI is a simple screening tool, not a full health assessment. It doesn't distinguish muscle from fat, so athletes and very muscular people can show a higher BMI without being overweight. It's also not designed for children, pregnant women, or the elderly in the same way as adults.
This calculator uses the standard adult BMI categories. BMI for anyone under 18 needs to be plotted on age- and gender-specific growth charts (BMI-for-age percentiles) rather than the fixed adult ranges shown here — a doctor or school health check is the right way to interpret it.
For adults, the WHO defines 18.5 to 24.9 as the "normal weight" range. Below 18.5 is classed as underweight, 25.0 to 29.9 as overweight, and 30.0 and above as obese.