BMI Calculator

Use our free BMI calculator to check your body mass index in seconds. It is free, needs no signup, and runs entirely in your browser. Enter your height and weight, in metric or imperial units, and you will get your BMI, your category and a simple colour-coded range bar.

What Is BMI?

Body mass index, or BMI, is a simple number calculated from your height and weight. It is weight in kilograms divided by height in metres squared. The result places you in a broad category: underweight, normal weight, overweight or obese. Health professionals use BMI as a quick screening measure because it is easy to calculate and gives a rough sense of whether weight is in a typical range for height.

BMI is not a perfect measure. It does not distinguish muscle from fat, it does not account for age, sex, bone density or where fat is carried, and athletes or very muscular people can score high without excess body fat. That is why this page states clearly that BMI is a general guide only and not medical advice. Use it as a starting point, and speak to a qualified health professional for advice about your own health.

How to Use the BMI Calculator

• Choose your height unit. Select centimetres, or feet and inches if you prefer imperial units.
• Enter your height. Type your height in centimetres, or in feet and inches, as accurately as you can.
• Choose your weight unit. Select kilograms or pounds.
• Enter your weight and click Calculate BMI. Your BMI, shown to one decimal place, appears with its category and a marker on the range bar.
• Start again if needed. Press Clear to reset the form.

Key Features and Benefits

• Metric and imperial. Use centimetres and kilograms, or feet, inches and pounds, without converting by hand.
• Instant result. Your BMI appears to one decimal place as soon as you click Calculate BMI.
• Clear category. See at once whether the result falls in the underweight, normal, overweight or obese range.
• Visual range bar. The coloured bar and marker show where your BMI sits across the four ranges.
• Private. Height and weight are processed in your browser and are never uploaded or stored.
• Free and unlimited. No signup and no limit on how many times you use it.
• Works on any device. The calculator is mobile-friendly and works in any modern browser.

Worked Examples

Example 1 - Metric. A person who is 175 cm tall and weighs 70 kg has a BMI of 22.9, which is in the normal weight range. The calculation is 70 divided by 1.75 squared, which is 70 divided by 3.0625.

Example 2 - Imperial. A person who is 5 feet 9 inches tall and weighs 154 pounds has a height of about 1.75 metres and a weight of about 69.9 kilograms, giving a BMI of about 22.8, also in the normal range. The calculator does both conversions for you.

Example 3 - A higher result. A person who is 170 cm tall and weighs 90 kg has a BMI of 31.1, which falls in the obese range. The range bar marker sits in the red section, making the category easy to see at a glance. Remember that this is a general guide only, and it does not by itself describe anyones health.

Frequently Asked Questions

What is a healthy BMI?

For most adults, a BMI from 18.5 to 24.9 is classed as normal weight. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese. These cut-offs are general screening ranges, not personal health targets, and they are not used in the same way for children.

Is BMI accurate for everyone?

No. BMI does not measure body fat directly. Muscular people, older adults, pregnant people and people of different ethnic backgrounds may find that BMI is less useful for them. Waist measurement, activity level and other health checks give a fuller picture.

Can I use BMI for a child?

Children are usually assessed with age- and sex-specific BMI percentiles rather than adult cut-offs. This calculator uses adult ranges, so it is not suitable as a child BMI assessment.

Is my height and weight stored?

No. The calculation runs in your browser. Your height and weight are not uploaded, saved or shared.

What should I do if my BMI is high or low?

Treat the result as a prompt, not a diagnosis. If you are concerned about your weight or health, speak to a doctor, dietitian or other qualified health professional, who can consider your full health history.

Related Tools

Try the Percentage Calculator for everyday maths, or the Word Counter for instant text counts.

For a fuller picture, many people use BMI alongside other simple checks, such as waist circumference, how active they are, and how they feel day to day. A single number rarely tells the whole story, so it is best to look at trends over time rather than one isolated result. If you recheck your BMI after a change in diet, exercise or lifestyle, use the same units and the same time of day for a fair comparison.