BMI Calculator
Body mass index is weight divided by height squared. It is a screening tool designed for populations, not a measure of body composition — but it is the number clinical thresholds and eligibility criteria are written in terms of, which is why it is worth knowing yours.
Your result
Fill in the fields on the left and your result appears here.
How BMI is calculated
BMI is weight in kilograms divided by height in metres squared. Imperial inputs are converted before the calculation, so the result is identical either way.
The categories are conventional cut-points applied to that figure: under 18.5 underweight, 18.5 to 24.9 healthy weight, 25 to 29.9 overweight, and 30 and above divided into three classes of obesity.
- Dividing by height squared is an approximation — it under-corrects for very tall people and over-corrects for very short ones.
- The cut-points were derived largely from populations of European ancestry, and lower thresholds are used in some countries for populations where metabolic risk rises at lower BMI.
- The healthy-weight range shown above is simply the weight range that produces a BMI between 18.5 and 24.9 at your height.
Track it, don't recalculate it.
Pep AI logs your weight, meals and protein alongside your schedule, so the numbers on this page turn into a trend instead of a one-off. Free on iOS and Android.
What BMI cannot tell you
BMI does not distinguish fat from muscle. A well-muscled person can register as overweight while carrying very little fat, and someone with low muscle mass can sit in the healthy range while carrying a great deal. It also says nothing about where fat is distributed, and abdominal fat carries different risk from the same amount elsewhere.
That is not a reason to dismiss it. At a population level BMI correlates well enough with health outcomes to be genuinely useful, and it costs nothing to measure — which is precisely why it became standard. The error is treating an individual reading as a verdict rather than as one input.
Waist circumference, waist-to-height ratio and a body-fat estimate all add information BMI does not carry, and taking two or three together gives a considerably better picture than any one alone.
Frequently asked questions
This calculator is general information for healthy adults, not medical or dietary advice. It applies published population formulas and cannot account for your clinical situation. Where a clinician has set you a target, that target replaces this one.
Built by the Pep AI team.