BMI calculator
Enter your height and weight in metric or imperial units to calculate your Body Mass Index and see which standard category it falls into. The calculation is instant and completely private.
How to use BMI Calculator
- 1
Choose your units
Switch between metric (cm, kg) and imperial (inches, lb).
- 2
Enter your height
Type your height in the selected unit.
- 3
Enter your weight
Type your weight in the selected unit.
- 4
Read your BMI
See your BMI and its category instantly, with the limits of BMI noted.
What BMI is and how it is calculated
Body Mass Index, or BMI, is a simple number that relates your weight to your height, and it is the most widely used screening measure for whether a person's weight is in a healthy range for their height. The calculation is straightforward: in metric units it is your weight in kilograms divided by the square of your height in metres, and this calculator handles the equivalent formula for imperial units automatically. The result is a single figure that places you on a standard scale. BMI is popular because it requires only two measurements that anyone can obtain, needs no special equipment, and gives a quick, consistent indication that is useful for tracking changes over time and for comparing against widely published categories. This tool computes it for you in either unit system, so you do not have to remember the formula or convert between pounds, stones, kilograms, inches and centimetres yourself — you just enter your height and weight and read the number.
See your category at a glance
A BMI number on its own means little without context, so this calculator also tells you which standard category your result falls into: underweight, normal weight, overweight, or obese, using the widely recognized thresholds. The category is colour-coded so you can take in your result at a glance rather than having to look up where your number sits on a chart. These categories come from the same internationally used ranges that health organizations and clinicians reference, which makes your result easy to interpret and to discuss. Seeing the band, not just the figure, turns an abstract number into something meaningful — it tells you immediately whether your weight is generally considered to be in a healthy range for your height or whether it sits above or below it. Because the category updates the instant you change your inputs, you can also see how a different weight would shift your classification, which is useful if you are setting a goal or tracking progress toward one.
Metric and imperial, no conversion needed
Height and weight are measured differently around the world, and converting between systems by hand is exactly the kind of fiddly step that introduces errors. This calculator removes it. With a single toggle you can work entirely in metric — centimetres and kilograms — or entirely in imperial — inches and pounds — and the correct formula is applied automatically for whichever you choose. You never have to convert your height into metres or your weight into kilograms, or remember the multiplier that imperial BMI requires. This matters because using the wrong units or mishandling a conversion produces a BMI that is badly wrong, which could be alarming or falsely reassuring. By letting you enter your measurements in the units you actually know them in, the tool keeps the input natural and the result accurate. Whether you think of your height in feet and inches or in centimetres, you can use the calculator without any mental arithmetic, and trust that the number it gives you is computed correctly for the units you selected.
Private by design — nothing is uploaded
Your height and weight are personal health information, and they deserve to be treated that way. In1 calculates your BMI entirely in your browser, so the measurements you enter never leave your device. Nothing is uploaded, nothing is stored, and there is no account or sign-up that links this data to you. The result appears instantly because there is no server involved, and the calculator works exactly the same offline as online. This local-only approach means you can check your BMI without registering sensitive health details with any website or wondering where that information might end up. It is a meaningful distinction for a health-related tool: many sites that look up such things transmit your data to a server, whereas here the entire calculation happens on your own machine and is forgotten the moment you close the tab. You get a quick, accurate result with the privacy that personal health figures warrant, which is the standard any tool handling this kind of information should meet.
Understand BMI's limits
BMI is a useful, quick screening tool, but it is important to understand what it does not tell you. Because it considers only height and weight, it cannot distinguish muscle from fat, so a very muscular, athletic person may register as overweight despite having low body fat. It does not account for where fat is carried, for bone density, or for differences related to age, sex and ethnicity, all of which affect what a given BMI means for an individual. It is a population-level measure that works well for general guidance but is not a diagnosis and should not be treated as the final word on anyone's health. This calculator states that plainly alongside your result, because the responsible way to present BMI is with its caveats attached. Use it as one helpful indicator and a way to track changes over time, but for a genuine assessment of your health, a qualified healthcare professional who can consider the full picture is the right source. The number is a starting point for understanding, not a verdict.
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