Calculators

BMI Calculator – Calculate Body Mass Index in Metric & Imperial

Work out your Body Mass Index (BMI) from height and weight in seconds with WHO categories.

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Fast, secure & processed 100% locally in your browser

About This BMI Calculator

This BMI calculator estimates your Body Mass Index from your height and weight, and tells you which World Health Organization weight category the result falls into. It is useful for anyone who wants a quick, numbers-based snapshot of where their weight sits relative to commonly used adult reference ranges — whether you are tracking a fitness goal, preparing for a doctor's appointment, or simply curious. The calculator supports both metric (kg and cm) and imperial (pounds, feet and inches) inputs, converts between them automatically, and displays your healthy weight range, how far you are from the nearest category boundary, and the exact formula it used.

BMI is a screening tool, not a diagnosis. It does not distinguish between muscle, fat and bone, so athletes and people with very high muscle mass often read as "overweight" while older adults may have a normal BMI despite low muscle mass. It is also not validated for children, pregnant women, or people under 20 in the same way it is for adults. Use this calculator as one data point among many and, if it raises any concerns, speak with a qualified healthcare professional.

How to Use the BMI Calculator

Choose your unit system — metric (kg / cm) or imperial (lb / ft + in).
Enter your age and, optionally, your gender. The BMI formula itself does not use gender for adults.
Type your height. In imperial mode you can enter feet and inches separately.
Type your weight in kg or pounds, depending on the mode you selected.
Click Calculate BMI. Your BMI, category, healthy weight range and distance to the nearest boundary appear instantly.
Use Copy, Print or Export to save the summary for your records.

Key Features

Metric and imperial units — switch between kg / cm and lb / ft + in at any time.
WHO adult categories — underweight, normal, overweight and obesity classes I–III.
Healthy weight range — the kg (or lb) span that would put you between BMI 18.5 and 24.9.
Distance to nearest boundary — how many kg or lb separate you from the next category.
Visual gauge — see at a glance where your BMI sits on the standard adult scale.
Category notes — a short plain-language summary for each result.
Formula shown — the calculator displays exactly which equation it used.
Session history — keep the last few results visible while you experiment.
Copy, print and export the summary as text for your notes or a doctor visit.

Frequently Asked Questions

What is BMI and how is it calculated?

BMI (Body Mass Index) is a single number derived from your height and weight. The metric formula is BMI = kg ÷ m² — for example, 70 kg at 1.70 m gives 70 ÷ (1.70 × 1.70) ≈ 24.2. The imperial formula is BMI = 703 × lb ÷ in². Both give the same result for the same person.

What is a healthy BMI range for adults?

The World Health Organization considers a BMI between 18.5 and 24.9 as the "normal weight" range for adults aged 20 and over. Below 18.5 is classified as underweight, 25.0–29.9 as overweight, and 30.0 and above as obesity, which is further split into classes I, II and III.

Does BMI apply to children and teenagers?

Not in the same way. Children and adolescents are still growing, so their BMI is interpreted using age- and sex-specific percentile charts rather than fixed adult cut-offs. If you are calculating for someone under 20, use a paediatric BMI percentile tool instead of the adult categories shown here.

Why might BMI give a misleading result?

BMI cannot tell the difference between muscle, fat, and bone. Muscular athletes often register as "overweight" despite low body fat, and older adults can have a normal BMI with relatively little muscle. It also does not account for where fat is stored, which matters for health risk. BMI is best used as a rough screening tool alongside other measures such as waist circumference and body composition.

Is my data sent anywhere?

No. Everything runs inside your browser using JavaScript. Your height, weight, age and results are calculated locally and stored only in the page's memory — they are cleared as soon as you refresh or close the page. Nothing is uploaded to a server.