BMI Calculator

What this calculator does

The BMI Calculator computes Body Mass Index from your height and weight and places the result in one of the four standard adult categories: Underweight below 18.5, Healthy Weight 18.5–24.9, Overweight 25.0–29.9, and Obesity 30.0 and above.

It works in metric (kg and cm) or imperial (lb, ft and in) and converts internally, so the same underlying formula produces both answers. Quick-select buttons cover common weights from 50 to 100 kg and heights from 150 to 190 cm.

Beyond the single number it shows the healthy weight range for your height in both kg and lb, a weight-change calculator for reaching a target, and a BMI-change calculator. The page also carries its own sections on athlete limitations and BMI during pregnancy, because those are the two cases where the number misleads most often.

How to use it

1. Choose your unit systemMETRIC (kg, cm) or IMPERIAL (lb, ft, in). The engine converts imperial input to metres and kilograms internally, so switching units changes the inputs and not the result.
2. Enter height and weightMetric takes centimetres and kilograms; imperial takes feet plus inches and pounds. Decimals are accepted, and the quick-select buttons are there when you just want a nearby round figure.
3. Press CALCULATE BMIThe result appears with one decimal place and the category it falls into, along with the standard range for that category.
4. Read the healthy weight range for your heightBelow the result the tool inverts the formula to show the weight range corresponding to BMI 18.5 to 24.9 at your height, in both kilograms and pounds. This is usually more actionable than the index itself.
5. Use the weight-change and BMI-change sectionsThese answer the two follow-up questions directly: what weight would put me at a given BMI, and what BMI would a given weight produce. Both use the same formula in reverse.

What the results mean

Underweight — below 18.5

The BMI falls below the standard adult healthy-weight range. As with every category this is a population band, not a diagnosis; a small frame and a genuine nutritional problem produce the same number.

Healthy Weight — 18.5 to 24.9

Within the standard adult range. It is a wide band by design, because height and weight alone cannot resolve build, muscle mass or fat distribution.

Overweight — 25.0 to 29.9

Above the standard healthy-weight range for adults. This is the band where muscular people are most often misclassified, which the page's own athlete-limitation section addresses.

Obesity — 30.0 and above

Within the obesity classification for adults. The tool reports the category and the range; what it means for any individual is a clinical question.

The healthy weight range for your height

Derived by rearranging the formula: 18.5 × height² and 24.9 × height², rounded to one decimal place and shown in kg and lb. Because BMI scales with the square of height, that range widens noticeably as height increases.

The formula

These are the expressions the calculator evaluates, written out so you can reproduce any result by hand.

Worked example

Limits worth knowing

A browser can only report what the platform gives it. These are the honest boundaries of this page, so a result is never read as more than it is.

• BMI does not measure body fat. It is height and weight only, so it cannot distinguish muscle from fat, and it says nothing about where weight is carried — which is the part that matters clinically. The page's own FAQs on body fat and accuracy say the same.
• The four categories shown are the standard adult bands. They are not applicable to children or teenagers, who are assessed against age-and-sex percentile charts instead, and the page states this in its own children and teenagers FAQs.
• It is misleading for muscular and athletic builds. Dense muscle weighs more than fat for the same volume, so trained people frequently land in Overweight while carrying little fat. The page ships a dedicated Important Athlete Limitation section for exactly this reason.
• It is not appropriate during pregnancy, and the page has a section saying so. Pre-pregnancy BMI is what clinicians use; a figure calculated during pregnancy does not mean what the categories imply.
• This is a calculator, not a medical assessment. It cannot account for age, sex, ethnicity, frame size, health conditions or medication, and no result here should replace a conversation with a clinician.

Tips

• Weigh yourself the same way each time — same time of day, similar clothing — if you plan to track the number. Day-to-day fluctuation of a kilogram or two is normal and will move BMI by several tenths.
• The healthy weight range is more useful than the index. It converts an abstract number into kilograms you can actually act on.
• Measure your height rather than recalling it. Height is the squared term, so a 3 cm error moves BMI more than a 1 kg weight error does.

Troubleshooting

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