BMI Calculator

Enter your height and weight in the tool above, and it will work out your Body Mass Index (BMI), show your category, and give the healthy-weight range for your height. For example, a height of 175 centimetres and a weight of 70 kilograms gives a BMI of 22.9, labelled Normal weight, with a healthy weight range of roughly 56.7 kg to 76.3 kg.

Last tested: 1 November 2026.

Disclaimer: this page gives general information only. It does not give medical advice, diagnose any condition, or replace a healthcare professional. If you are worried about your weight or health, talk to a clinician who can see your full history.

How to use this BMI calculator

1. Choose your height unit: centimetres, or feet and inches.
2. Enter your height.
3. Choose your weight unit: kilograms or pounds.
4. Enter your weight, then click Calculate BMI.

Read your BMI, your category, and the healthy weight range for your height. If you enter a missing or impossible height or weight, the tool shows a plain error instead of a result.

A worked example from the live tool

With a height of 175 centimetres and a weight of 70 kilograms, the tool shows: “Your BMI is 22.9 — Normal weight.” It also shows: “For a height of 175 cm, a healthy weight range (BMI 18.5–24.9) is roughly 56.7 kg to 76.3 kg.” An imperial check, 5 feet 9 inches and 154 pounds, gives a BMI of 22.7, also labelled Normal weight, with a range of roughly 56.8 kg to 76.5 kg.

How the formula works, with sources

BMI is weight in kilograms divided by height in metres squared. In symbols, BMI = weight (kg) ÷ height (m)². For 175 centimetres and 70 kilograms, height in metres is 1.75, so the calculation is 70 ÷ (1.75 × 1.75) = 22.9, rounded to one decimal place. The tool converts pounds by multiplying by 0.45359237 and converts feet and inches by 0.0254 per inch, so the same formula applies in either unit system.

The category boundaries used here follow the adult categories published by the Centers for Disease Control and Prevention (CDC), About Body Mass Index, and CDC, Adult BMI Categories, and the method is also described by the NHS, Calculate your body mass index. The table below compares those published category names with the labels this tool shows.

The numbers match; only the middle label differs, and this tool does not split obesity into classes. Keep that label difference in mind when you compare the result with a clinic or health-service page.

What BMI cannot see

BMI adjusts weight for height, but it cannot see body composition. It does not distinguish muscle from fat, bone density, or where fat is carried, and it does not measure fitness, diet, or blood pressure. Two people with the same BMI can have very different amounts of muscle and fat, so a high BMI does not by itself mean a person is unfit, and a BMI in the middle range does not by itself rule out a health risk. Waist circumference, waist-to-height ratio, body fat percentage, and blood pressure can add context, but they are not part of this tool.

Who should not use adult cut-offs

The adult cut-offs above do not apply in the same way to children and teenagers, for whom BMI is interpreted using age- and sex-specific charts, or to pregnant people, and they can be misleading for very muscular people and some athletes. Ethnicity can also affect interpretation: some populations develop health risks at lower BMI thresholds than the standard cut-offs suggest. If any of these apply to you, treat the result as a rough guide only and talk to a clinician about what it means for you.

Limits and common mistakes

• Measure height without shoes, standing straight, and weigh yourself at a similar time of day, in similar clothing, on the same scale, because weight fluctuates naturally with hydration, meals, and clothing.
• Do not round your height or weight before you enter it; small errors change the result, especially for shorter heights.
• A single BMI is a snapshot. Repeated measurements over weeks show a trend better than one day’s number.
• A height over 3 metres, or a missing or zero weight, returns a plain error, not a result.
• This page gives general information only. It does not diagnose any condition or replace a healthcare professional.

Privacy note

Your height and weight stay in your browser and are never sent to a server or stored by this tool. If you have a question about this page, use the contact page.

Related tools

Try the age calculator to work out exact age in years, months and days, the unit converter to switch between metric and imperial units for length, weight, and temperature, and the percentage calculator for a share or a change. See all of them on the calculators hub.

Frequently asked questions

What is a good BMI?

For most adults, a BMI between 18.5 and 24.9 is considered the healthy range. Below 18.5 is underweight, 25 to less than 30 is overweight, and 30 or above is in the obesity range. This tool labels the middle range “Normal weight”.

Is BMI accurate for muscular people?

Not always. BMI cannot distinguish muscle from fat, so very muscular people can have a high BMI without a high amount of body fat. In that case, the category alone is misleading.

Can children use this calculator?

Children and teenagers should not be judged by the adult cut-offs on this page. Their BMI is interpreted using age- and sex-specific charts, so a clinician or school health service should interpret a child’s result.

Why does my BMI change during the day?

Weight fluctuates naturally with hydration, meals, clothing, and the time of day, so a scale reading can shift by a kilogram or more. Weigh yourself at a similar time, in similar clothing, and look at the trend over weeks rather than one day’s number.

Is my height and weight uploaded or stored?

No. The calculation runs entirely in your browser. Your measurements are never sent to a server or stored by this tool.

What should I do if the result worries me?

Talk to a clinician who can see your full history. This page gives general information only and does not diagnose any condition or replace a healthcare professional.

Healthy-weight range by height (BMI 18.5-24.9, adults)

This chart is computed from weight = BMI x height in metres squared, rounded to one decimal. It shows a band, not a single target weight, and it uses adult cut-offs only. Children use age and sex charts, and the muscle and pregnancy caveats already on this page still apply. The 175 cm row checks against the live tool: 56.7-76.3 kg.

Obesity classes, and what this tool shows

Published obesity classes are 30.0-34.9, 35.0-39.9, and 40.0 or above. All three map to this tool’s single label, Obese. The tool does not report a class.

How to read the result: the tool shows three labelled boxes, the BMI number, the category using the tool’s label, and the healthy-weight range for the entered height. This page gives general information only and does not give medical advice.