How it works
Metric input uses weight in kilograms divided by height in metres squared. Imperial input converts height to metres and weight to kilograms first, so the same person produces the same BMI in either unit system. The WHO bands then label the result.
- BMI is a screening number, not a diagnosis; muscle mass, age and body composition are not part of it.
Why it matters
BMI is used in forms, insurance and clinical triage because it needs only two measurements. The danger is treating a screening threshold as an individual verdict, especially in athletes or older adults where the number misclassifies body composition.
A worked example
A 175 cm adult weighing 70 kg has a BMI of 70 ÷ 1.75² = 22.9, in the normal WHO band. Converted to 68.9 inches and 154.3 pounds, the same person still reads 22.9.
Common mistakes
- Mixing metres and centimetres in the height input.
- Applying adult bands to children.
- Treating BMI as a measure of health or body fat.
Practical tips
Pair BMI with waist measurement and trends over time rather than a single reading. If the number matters for a medical decision, use it as one input among several, with a clinician doing the interpretation.
How to use it
- Open the tool. Everything runs in your browser tab.
- Paste or type your input, then choose the action you need.
- Check the result and copy it with one click.
Common questions
Is BMI a diagnosis?
No. It is a screening number. Muscle mass, age, sex and body composition are not part of the formula.
Why does BMI stay the same after switching units?
Switching cm/kg to in/lb converts the height and weight values, so the same person keeps the same BMI.
Which BMI bands are used?
The standard WHO screening bands: under 18.5, 18.5-24.9, 25-29.9 and 30 or above.
Is this tool really free?
Yes. There is no account, no paywall and no usage limit. Tools App is funded by aumenso, the studio behind it.
Is anything I enter uploaded?
No. The tool runs in your browser tab; what you enter is never sent to us and never stored.