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BMI Calculator — Body Mass Index, Free & Instant

Body Mass Index with category. Works entirely in your browser. Your files never leave your device.

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What is BMI Calculator?


BMI Calculator is a free tool that calculates your Body Mass Index from your height and weight. BMI is a widely used screening number defined as weight in kilograms divided by height in meters squared. The calculator supports both metric (cm, kg) and imperial (feet/inches, pounds) inputs and shows your result alongside the standard weight category ranges.


The standard BMI categories are: underweight (below 18.5), healthy weight (18.5–24.9), overweight (25–29.9), and obese (30 and above). These thresholds were established by the World Health Organization and are used globally as a general health screening tool. BMI does not distinguish between muscle and fat mass, so athletes and very muscular individuals often measure as overweight despite being healthy.


BMI is most useful as a quick initial screening for potential weight-related health risks, not as a definitive health assessment. A doctor or dietitian uses BMI alongside other measures like waist circumference, blood pressure and blood glucose to get a full picture. The calculator is free, private and works entirely in your browser with no data stored.


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Instant results
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100% private
Files stay on your device
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Always free
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Mobile ready
Works on any device


How to use BMI Calculator


  1. Enter your height — choose centimeters or feet and inches
  2. Enter your current weight in kilograms or pounds
  3. Click Calculate to get your BMI value and category instantly
  4. Review the healthy BMI range and what your result means


Why use OnlineToolsPlus?


OnlineToolsPlus processes everything locally in your browser. Your files, text and data never leave your device, which eliminates server-side privacy risks. With 200+ free tools covering PDF, image, AI writing, developer utilities, calculators, SEO, color tools and more, there is no need to juggle multiple subscriptions or install software.


Frequently asked questions


Is BMI an accurate measure of health?
BMI is a rough population-level screening tool, not a precise individual health assessment. It does not distinguish between muscle and fat, does not account for fat distribution, and has known limitations across different ethnicities and age groups. Use it as one data point alongside other health indicators.


Does it support metric and imperial units?
Yes. Enter height in cm or feet and inches, weight in kg or pounds. The tool converts as needed.


What BMI is considered healthy?
The WHO classifies 18.5 to 24.9 as normal weight for adults. Under 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese. These are statistical ranges, not individual diagnoses.


Is BMI calculated differently for children?
Yes. Children and teens use BMI-for-age percentiles rather than fixed ranges. This tool is calibrated for adults.


Does it send my data anywhere?
No. All calculations run locally.


Should I see a doctor if my BMI is outside the normal range?
A BMI outside the normal range is worth discussing with a healthcare provider, but it is not a diagnosis. Many factors affect health that BMI does not measure.


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Last updated: April 11, 2026

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