BMI calculator

Calculate your BMI in metric or imperial units, see your WHO category on a visual scale and the healthy weight range for your height.

How to Calculate BMI

1
Choose metric or imperial units
Switch between centimetres and kilograms or feet, inches and pounds, whichever your scale and tape measure use.
2
Enter height and weight
Type in your height and weight. The result recalculates as soon as you change either field.
3
Read your BMI, category and healthy range
See your BMI to one decimal place, its WHO category on a visual scale, and the weight range considered healthy for your height.

How BMI and the WHO categories are worked out

Body mass index is weight in kilograms divided by height in metres squared, a single formula regardless of which units you type into the form. Imperial measurements are converted to metric before anything else happens. The eight WHO categories, from severe thinness to obese class III, are looked up from your exact BMI, not from the number rounded for display, so a BMI of 18.51 already counts as normal weight even though it is shown as 18.5.

What the healthy weight range means

The healthy range shown under your result is the span of weights that would put someone of your exact height inside the WHO's normal-weight band, from a BMI of 18.5 up to 24.9. It is a population-level guideline, not a personal target: BMI does not distinguish muscle from fat, so an athlete with a lot of muscle mass can show a higher BMI than the chart implies is healthy for them.

Your height and weight never leave this tab

This calculator runs entirely in JavaScript in your browser. There is no upload, no account and no server involved in turning your height and weight into a BMI figure. The numbers exist only on this page until you close or refresh it.

Frequently asked questions

Does the BMI scale apply to children?

No. This calculator is built for adults aged 18 and older. Children and teenagers grow at different rates, so pediatric BMI is judged against age- and sex-specific growth charts instead of the fixed adult categories used here.

How accurate is BMI for athletes with a lot of muscle?

Less accurate than for most people. BMI only looks at height and weight, so it cannot tell muscle from fat. A muscular athlete can land in the overweight range on this scale while carrying very little body fat.

What is the healthy weight range shown under my result?

It is the range of weights that would give someone of your exact height a BMI between 18.5 and 24.9, the WHO's normal-weight band. Switch units and the same range is shown converted to pounds or kilograms.

What is the difference between obese class I, II and III?

They are the same category split into three bands of increasing BMI: class I from 30 to 34.9, class II from 35 to 39.9, and class III from 40 upward. The split exists because health risk keeps rising within what is otherwise one broad WHO category.

Does my data get sent to a server?

No. Height and weight are read from the two fields on this page and the whole calculation happens locally in your browser. Nothing is uploaded or stored anywhere.

How do I convert my height from centimetres to feet and inches?

Switch the units toggle at the top of this calculator to imperial. Your BMI and healthy range recalculate immediately in the new units, and the unit converter tool handles plain length conversions if that is all you need.

Can I switch units without losing my numbers?

Yes. Toggling between metric and imperial converts your existing height and weight instead of clearing the fields, so you can compare both without retyping anything.