BMI Calculator — Body Mass Index with Category, Free & Private
Calculate your Body Mass Index and see your weight category (underweight, normal, overweight, obese) based on WHO guidelines. Supports metric and imperial. Runs in your browser — no data sent anywhere.
How to use this tool
- Enter your height and weight.
- Select metric or imperial units.
- Read your BMI value and category.
About BMI Calculator
The BMI Calculator works out your Body Mass Index, a single number that relates your weight to your height and gives a rough sense of whether you fall in a healthy weight range. Pick metric or imperial, enter your weight and height, and the result appears instantly. In metric you enter weight in kilograms and height in centimetres; in imperial you enter weight in pounds and height in feet and inches. The tool converts everything to kilograms and metres internally, so both systems return the same figure.
The math is the standard BMI formula: weight in kilograms divided by height in metres squared. A person weighing 70 kg at 1.75 m has a BMI of 70 / (1.75 x 1.75), which is about 22.9. The result is rounded to one decimal place and sorted into the four World Health Organization categories: underweight below 18.5, normal weight from 18.5 up to 25, overweight from 25 up to 30, and obese at 30 and above. Each category is colour-coded so you can read the verdict at a glance.
BMI is a screening tool, not a diagnosis. Because it uses only height and weight, it cannot tell muscle from fat. A muscular athlete can register as overweight while carrying very little fat, and an older person who has lost muscle can score as normal while having more fat than is ideal. It also says nothing about where fat sits, which matters for health, and the standard adult thresholds do not apply to children, pregnant women, or some ethnic groups for whom different cut-offs are recommended. Treat the number as a starting point for a conversation with a clinician rather than a final word.
This is general health information, not medical advice. The calculation runs entirely in your browser, so your weight and height are never uploaded or stored. Use the result to track trends over time alongside other measures such as waist circumference, blood pressure, and how you actually feel and move, and speak to a doctor before making significant changes to your diet or exercise based on a single figure.
Frequently Asked Questions
- What BMI formula does this use?
- It uses the standard metric formula: weight in kilograms divided by height in metres squared. When you choose imperial, your pounds are converted to kilograms and your feet and inches to metres first, so imperial and metric inputs produce the same BMI value.
- What are the BMI categories?
- The tool uses the World Health Organization adult ranges: below 18.5 is underweight, 18.5 to under 25 is normal weight, 25 to under 30 is overweight, and 30 or above is obese. Your result is placed in one of these four bands and shown in a matching colour.
- Is BMI accurate for everyone?
- No. BMI only compares weight to height and cannot distinguish muscle from fat or show where fat is stored. It tends to overstate body fat in muscular people and understate it in those with low muscle mass. The standard adult thresholds also do not apply to children, pregnant women, or certain populations who have different recommended cut-offs.
- Does it support both metric and imperial units?
- Yes. Switch between metric (kilograms and centimetres) and imperial (pounds, feet, and inches) at the top of the tool. Internally everything is converted to kilograms and metres before the BMI is computed, so the result is consistent regardless of which system you enter.
- How precise is the result?
- The BMI is rounded to one decimal place, for example 22.9. That level of precision is appropriate because BMI is a screening estimate; reporting more decimals would imply an accuracy the measurement does not have, especially since home scales and height readings carry their own small errors.
- Is my weight and height data sent anywhere?
- No. The entire calculation happens locally in your browser. Nothing you type is uploaded to a server, saved to your device, or shared, so you can check your numbers privately.
- Should I use BMI to decide on a diet?
- Treat BMI as one input among several, not a diagnosis. It is useful for spotting trends and as a conversation starter with a healthcare professional. Combine it with measures like waist size and overall fitness, and consult a doctor before making major changes to your diet or activity.
Embed this tool on your site
Free. One line of HTML — the tool runs in your visitor's browser, no data sent to anyone.
<iframe src="https://brevio.pro/embed/bmi-calculator" width="100%" height="600" loading="lazy" style="border:1px solid #e5e5e5;border-radius:8px" title="BMI Calculator — brevio"></iframe> <p style="font:12px/1.4 sans-serif"><a href="https://brevio.pro/tools/bmi-calculator">BMI Calculator</a> by <a href="https://brevio.pro">brevio</a></p>