Want to work out your BMI? It’s straightforward: divide your weight in kilograms by your height in metres squared. That’s all you need. This short guide explains the exact calculation, what the result means for your health, and why it’s worth checking now and then. Skip the sums and use our free BMI Calculator to see your weight category in seconds.
Understanding how to calculate bmi
BMI stands for Body Mass Index. It’s a single number that gives a rough idea of whether your weight is in a healthy range for your height. It doesn’t measure body fat directly, but it’s a useful starting point because it’s quick, cheap and easy. All you need are two numbers: your weight in kilograms and your height in metres. Square the height, then divide the weight by that figure. For example, if you weigh 70 kg and are 1.75 m tall, your BMI is 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9. That puts you in the ‘healthy’ range, which is usually between 18.5 and 24.9.
The categories are simple. Below 18.5 is underweight, 18.5 to 24.9 is healthy, 25 to 29.9 is overweight, and 30 or above is obese. Children have different charts because their bodies are still growing, so don’t use the adult numbers for them. Also, BMI won’t tell you if you’re carrying extra muscle instead of fat, which is why athletes sometimes get misleading results.
How to work it out, step by step
- Enter your weight in kilograms.
- Enter your height in centimetres.
- Your BMI and weight category (underweight, normal, overweight, obese) appear instantly.
BMI = weight (kg) ÷ height (m)²Why it matters
The danger comes when people take the number too seriously. A high BMI might just mean you’ve got a lot of muscle—think rugby players or weightlifters—but most of the time it’s a sign you’ve got more fat than is healthy. The real issue is when people ignore it until their clothes stop fitting or a doctor brings it up. If you’re in the overweight or obese range, it’s worth speaking to your GP about what that might mean for your long-term health, not just your waistline.
Free tools for this
| Tool | What it does |
|---|---|
| BMI Calculator | Find your Body Mass Index (BMI) and weight category in seconds. |
| Ideal Weight Calculator | Estimate a healthy target weight range for your height and gender. |
| BMR Calculator | Find how many calories your body burns at rest and each day. |
Try the BMI Calculator
Skip the manual maths — enter your numbers and get the answer instantly.
Open the BMI Calculator →Good to know
Remember that these figures are general guides, not medical advice. Bodies differ, so treat the result as a starting point and speak to a qualified professional before making decisions about your health.
Key takeaways
- Weigh yourself in kilograms and measure your height in metres (without shoes).
- Square your height, then divide your weight by that number to get your BMI.
- Check the result against the standard categories to see where you stand.
Frequently asked questions
What is a healthy BMI?
For adults, a BMI between 18.5 and 24.9 is generally considered the healthy range. Below 18.5 is classed as underweight, 25 to 29.9 as overweight, and 30 or more as obese.
Is BMI accurate for athletes?
Often not. Muscle is denser than fat, so a very muscular person can land in the overweight or obese category while carrying very little fat. If you train seriously, a body-fat measurement tells you far more than BMI does.
Does BMI work for children?
No. Children and teenagers are assessed using age- and sex-specific BMI percentiles, because healthy ranges change as they grow. This calculator uses the adult categories only.
What units does it take?
Kilograms for weight and centimetres for height. If you work in pounds and feet, convert first: one pound is about 0.4536 kg, and one foot is 30.48 cm.
Why does the healthy weight range matter more than the BMI number?
Because a range in kilograms is something you can act on. The calculator shows the weight span that corresponds to a BMI of 18.5 to 24.9 at your height, which is easier to interpret than a single index value. It is still a guide, not a target set by a clinician.
