BMI Calculator
Enter height and weight in metric or imperial units to get your body mass index and the WHO adult category it falls in. It is for adults aged 20 and over, it is a screening number rather than a diagnosis, and your inputs stay in your browser.
Runs in your browser
Free, no sign-up. BMI is calculated in your browser. Height and weight are never uploaded, stored, put in a link, or sent to analytics; events record only that a calculation happened.
BMI Calculator
Calculate body mass index with metric or imperial inputs.
Enter height and weight, then choose your preferred units to calculate BMI.
How to use the BMI Calculator
- Use the cm / in switch to choose the unit for Height and the kg / lb switch for Weight. Switching a unit converts the number already typed, rounded to one decimal.
- Type your height and weight.
- Read the Result panel: the BMI to one decimal place, the category, and the WHO range it sits in.
- If a value is zero, negative, not a number, or outside the supported range (0.5-2.8 m and 2-700 kg), the panel shows an error instead of a BMI. Press Reset to clear everything.
Worked example
Sample data
Height: 175 cm Weight: 70 kg
BMI 22.9 Category: Normal (WHO range 18.5 - 24.9)
175 cm is 1.75 m, and 70 / (1.75 x 1.75) = 22.86, shown as 22.9. The same person entered as 69 in and 154 lb gives 22.7 because the imperial numbers are rounded.
How it works
The formula
BMI is weight divided by height squared. Imperial inputs are converted to kilograms and metres first (1 in = 2.54 cm, 1 kg = 2.2046226218 lb), which gives the familiar shortcut of about 703 times pounds divided by inches squared.
The result is rounded to one decimal place before the category is chosen, so 24.95 would show as 25.0 and be classed as Overweight.
BMI = weight (kg) / height (m)^2 Imperial shortcut: BMI = 703 x weight (lb) / height (in)^2
WHO adult categories used
The tool shows four bands: Underweight below 18.5, Normal 18.5 to 24.9, Overweight 25 to 29.9, and Obese 30 and above. The Obese band is not split into classes I, II and III.
These cut-offs are for adults aged 20 and over. Children and teenagers are assessed against age- and sex-specific growth charts, so this tool is not suitable for them.
What BMI cannot tell you
BMI uses only height and weight. It does not measure body fat, muscle, bone density or where fat is carried, so it can misclassify people who are very muscular, older, or from populations where health risks begin at lower BMI values. It is also not designed for pregnancy. Use it as one screening number and talk to a clinician about what it means for you.
Inputs, outputs and limits
Inputs
- Height in cm or inches
- Weight in kg or pounds
Outputs
- BMI to one decimal place
- WHO adult category
- The WHO range for that category
Limits
- Adults aged 20 and over only; not for children, teenagers or pregnancy.
- Not a diagnosis. Athletes and people with high muscle mass can be misclassified.
- Uses the standard WHO cut-offs; it does not apply lower, population-specific cut-offs.
- Accepts heights from 0.5 to 2.8 m and weights from 2 to 700 kg.
Processing
- BMI is calculated in your browser. Height and weight are never uploaded, stored, put in a link, or sent to analytics; events record only that a calculation happened.
Frequently asked questions
Is my height and weight saved or sent anywhere?
No. The calculation runs in this page's JavaScript. Nothing is uploaded or stored, there is no share link for this tool, and analytics never receive the values or the result.
Can I use this for my child or teenager?
No. Under 20, BMI is interpreted against growth charts for the child's age and sex, not the adult bands used here. Ask a paediatrician or school nurse.
Is a normal BMI the same as being healthy?
No. BMI is a quick screening number. It says nothing about fitness, diet, blood pressure, blood sugar or body fat, so a normal BMI does not rule out health problems and an overweight BMI does not prove them.
Why might my result be misleading?
Muscle weighs more than fat, so athletes and strength trainers often read as overweight. Older adults can have a normal BMI with little muscle. Some Asian and other populations are at higher risk at lower BMI values than the standard cut-offs.
Does it work during pregnancy?
No. Weight changes in pregnancy are expected and are tracked by your midwife or doctor with different guidance.
Why did my imperial and metric answers differ slightly?
Converting a typed value rounds it to one decimal place, and the BMI is rounded to one decimal. Enter exact values in one system to avoid the small gap.
Scope, sources and limitations
- Applies to
- Adults aged 20 and over, WHO standard BMI cut-offs. Not for children, teenagers or pregnancy.
- Last reviewed
- Not yet independently reviewed. Check results against the sources below.
- Sources
- A screening measure, not a medical diagnosis.
- Not valid for children, teenagers or pregnancy.
- Does not measure body fat or muscle; athletes and older adults can be misclassified.
- Some populations have lower WHO-recommended action points; ask a clinician.
Need this workflow inside your product?
We build calculators, converters and processing steps like this one directly into your web or mobile product, with your rules and branding.