BMI Calculator Online Tool
BMI Calculator and health category instantly. Free, offline, client-side - your data stays in your browser. Metric and imperial.
Calculate your Body Mass Index with the standard WHO formula. Runs entirely in your browser — no health data leaves your device.
How to Use BMI Calculator Online Tool
- Pick your unit system. Use the dropdown to choose Metric (kilograms and centimetres) or Imperial (pounds and inches). The weight and height labels update automatically so you always know which unit you are entering.
- Enter your weight. Type your weight into the first number field. Decimals are allowed (e.g. 72.5 kg). The default is 70 kg, shown as a placeholder you can overwrite.
- Enter your height. Type your full height - not just the decimal part. For 1.75 m, type 175 in metric, or 69 in imperial. Decimals work here too.
- Calculate. Click "Calculate BMI" or press Ctrl+Enter (Cmd+Enter on Mac). Your BMI appears in big colour-coded numbers below, along with the WHO category.
- Read your category and healthy range. The result line shows whether you are Underweight (blue), Normal (green), Overweight (amber), or Obese (red), plus the healthy weight range for your specific height in the unit you picked.
- Copy or save the result. Click "Copy result" to put a short text summary on your clipboard, or "Download .txt" to save a timestamped report with your inputs and calculated BMI.
- Try different unit systems. Switching between Metric and Imperial updates the labels but keeps the number you typed - re-enter your values in the new unit before recalculating.
Frequently Asked Questions
Is my data secure when using this calculator?
Yes. All BMI calculations happen entirely in your browser using client-side JavaScript. No personal health data is uploaded to any server or stored anywhere.
Is this BMI calculator free to use?
Yes, this tool is completely free with no limits on usage. Calculate your BMI as many times as you need without any subscriptions or hidden fees.
Does this work offline?
Yes. Once the page loads, all calculations work offline. You can bookmark this page and use it anytime without an internet connection.
What units does this calculator support?
The calculator supports both metric (kilograms and centimetres) and imperial (pounds and inches) units. Toggle between the two systems using the dropdown menu at the top.
What is a healthy BMI range?
A healthy BMI typically falls between 18.5 and 24.9. Below 18.5 is considered underweight, 25-29.9 is overweight, and 30 or above is classified as obese according to WHO standards.
Is BMI accurate for everyone?
BMI is a useful screening tool but has limitations. It does not account for muscle mass, bone density, or body composition. Athletes or very muscular individuals may have high BMI without excess fat.
Can children use this BMI calculator?
This calculator uses the standard adult BMI formula. For children and teenagers, BMI must be interpreted using age- and gender-specific percentile charts. Consult a paediatrician for accurate child BMI assessment.
How often should I check my BMI?
For general health monitoring, checking your BMI once every few months is sufficient unless you are actively working on weight management goals. Daily checks are not necessary as healthy weight changes occur gradually.
What should I do if my BMI is outside the healthy range?
If your BMI indicates you are underweight or overweight, consult with a healthcare provider before making major lifestyle changes. They can assess your overall health and recommend appropriate diet and exercise plans.
Why do metric and imperial calculations give slightly different results?
Both systems use the same BMI formula, but rounding during unit conversion can cause minor differences in the final number. The difference is typically negligible and does not affect your BMI category.