⚖️ BMI Calculator
Compute your Body Mass Index and see your health category. A quick general indicator of weight status (not medical advice). Free, unlimited, private — works entirely in your browser.
How to use
- Enter your height — switch between centimetres and feet/inches using the unit toggle at the top.
- Enter your weight in kilograms or pounds, matching the unit system you chose.
- Click 'Calculate BMI' to see your Body Mass Index instantly, along with your health category.
- Read the category (Underweight, Normal, Overweight, Obese) and the healthy weight range for your height.
FAQ
Is it really free?
Yes — every tool on this site is 100% free with no limits, no signup and no watermarks.
Is my data private?
Absolutely. All processing happens locally in your browser. Your files are never uploaded to any server.
What is the BMI formula?
BMI = weight (kg) ÷ height (m)². In imperial units: BMI = 703 × weight (lb) ÷ height (in)². The calculator applies the formula automatically — you just enter height and weight.
What are the BMI categories?
The WHO standard categories are: under 18.5 Underweight, 18.5–24.9 Normal weight, 25–29.9 Overweight, and 30+ Obese (with 30–34.9 Class I, 35–39.9 Class II, 40+ Class III). These cut-offs are the same for adult men and women.
Is BMI accurate for athletes or muscular people?
Not always. BMI cannot distinguish muscle from fat, so very muscular people may score as 'overweight' despite low body fat. Similarly, it can underestimate risk in older adults with low muscle mass. Treat BMI as a screening tool, not a diagnosis — waist circumference and body-fat percentage give a fuller picture.
Does BMI work for children and teenagers?
Children's BMI is interpreted differently — using age- and sex-specific percentiles rather than the adult cut-offs — because healthy body composition changes as kids grow. This calculator uses the adult scale; for under-18s, consult a paediatric growth chart or your doctor.
📘 Complete Guide to Body Mass Index
Body Mass Index (BMI) is the world's most widely used quick check for weight-related health risk. It takes ten seconds to compute, needs no equipment beyond a scale and tape measure, and correlates reasonably well with body fat at population level. This guide explains what the number means, where it falls short, and how to use it wisely alongside other measures.
A brief history
BMI was devised in the 1830s by Belgian statistician Adolphe Quetelet as the "Quetelet Index" — a way to describe the "average man," not to judge individual health. It was revived in the 1970s by physiologist Ancel Keys, who found it the best simple proxy for body fat among easy measurements, and the WHO adopted its now-familiar cut-offs in the 1990s. Knowing this history helps: BMI was designed as a population statistic that got drafted into personal health duty.
Reading your result
A BMI of 22, for example, sits comfortably in the normal range (18.5–24.9). The calculator also shows your healthy weight range for your height — arguably more actionable than the index itself, because it gives you a concrete target band in kilograms or pounds. Small fluctuations of 0.5–1 BMI point day to day are normal (water retention, meals, weighing at different times); trends over weeks matter, not single readings.
Limitations you should know
BMI ignores body composition (muscle vs fat), fat distribution (belly fat carries more risk than hip fat at the same BMI), age (older adults can have risky fat levels at "normal" BMI), sex, and ethnicity (some Asian populations face elevated diabetes risk at lower BMIs, and several countries publish adjusted cut-offs). Athletes, pregnant women, and the very tall or short should interpret results cautiously.
What to track alongside BMI
For a fuller picture, add waist circumference (over 94 cm for men / 80 cm for women signals increased risk in many guidelines), waist-to-height ratio (keep it under 0.5), and how you actually feel and move. If your BMI is outside the normal range and stays there, that is a good prompt for a conversation with a healthcare professional — not a verdict.
Privacy note
Height and weight are personal health data. This calculator processes everything locally in your browser; nothing is uploaded, stored, or shared.
📖 Step-by-step tutorial
New to this tool? Read our step-by-step guide to calculating your BMI online — with worked examples and practical tips.