BMI Calculator
Enter your height and weight to see your body mass index, WHO category and healthy weight range. Free, instant, private.
The arithmetic behind the number
Body mass index is weight in kilograms divided by height in metres squared. That single division is the entire calculation. There is no hidden adjustment for age, sex, frame size or anything else.
When you switch to imperial, this page does not use the familiar 703 shortcut. It converts first: feet and inches are added into total inches and multiplied by 0.0254 to get metres, and pounds are multiplied by 0.45359237 to get kilograms. The same metric division then runs. Because the conversion factors are exact, entering the same body in either unit system returns the same figure to the decimal place shown.
A worked example
Take someone 182 centimetres tall weighing 96 kilograms.
182 cm becomes 1.82 m. Squared, that is 3.3124. Then 96 divided by 3.3124 gives 28.98, which the page rounds and displays as 29.0. The category shown is Overweight, and the healthy weight range printed underneath is 61.3 kg to 82.5 kg, because 18.5 times 3.3124 is 61.28 and 24.9 times 3.3124 is 82.48.
The marker on the coloured bar sits at 56 per cent of the way across, because the bar maps a BMI of 15 to the far left and 40 to the far right, and 29 sits a little past the middle of that span.
The exact cut points used here
The category label comes from three comparisons in order: below 18.5 returns Underweight, below 25 returns Normal weight, below 30 returns Overweight, and anything else returns Obese.
Worth knowing: the labels printed under the scale bar read 18.5 to 24.9 and 25 to 29.9, but the code tests against 25 and 30. A BMI of 24.96 is therefore labelled Normal weight even though it rounds to 25.0 on screen. The healthy weight range is a separate calculation drawn at 18.5 and 24.9, so it is very slightly narrower at the top than the category boundary.
What this number can and cannot tell you
BMI was built to describe populations, not to assess one person. It has no way to tell muscle from fat, so a heavily built rugby player and a sedentary person of identical height and weight get the same score with very different bodies underneath.
It also says nothing about where weight sits. Two people at BMI 28 can have quite different waist measurements, and abdominal fat is the part clinicians usually care about most. Age changes body composition without changing the formula, and several health bodies apply lower thresholds for some populations than the ones used here.
It is not valid for children or teenagers, who are assessed against age and sex percentile charts rather than fixed adult numbers, and it is not meaningful during pregnancy.
None of that makes BMI useless. It is a cheap, repeatable number that flags when a conversation might be worth having. It is not a diagnosis, and nothing on this page is medical advice. If the result concerns you, a doctor can look at waist measurement, blood pressure, blood results and your history together, which is a far better picture than one ratio.
Related calculators
If you want an energy figure rather than a weight ratio, the Calorie Calculator estimates resting metabolic rate and daily maintenance calories from the same height and weight inputs. To convert between stones, pounds and kilograms before entering a figure here, use the Unit Converter. If you are tracking change over a period, the Date Difference Calculator will count the exact days and weeks between two weigh-ins.
Questions people ask
Is a BMI of 29 something to worry about?
On its own, no single number answers that. A 29 sits in the overweight band under the thresholds this page uses, but a muscular person and someone carrying significant abdominal fat can both land there. It is a reason to check in with a doctor, not a verdict.
Does this page use the 703 imperial formula?
No. It converts inches to metres and pounds to kilograms using exact factors, then runs the metric division. The 703 multiplier is a rounded approximation of that conversion, so results here can differ from a 703-based calculator in the second decimal place.
Can I use this for a child?
Not meaningfully. The adult cut points do not apply to growing bodies. Paediatric BMI is read against age and sex percentile charts, which this tool does not include.
How is the healthy weight range worked out?
It reverses the formula. Your height in metres is squared, then multiplied by 18.5 for the lower figure and 24.9 for the upper one. In imperial mode those two kilogram values are divided by 0.45359237 to display as pounds.
Is anything I type here sent away?
Nothing is sent anywhere. Everything runs in your browser, so your height and weight never leave your device. No figure is uploaded, logged or stored between visits.