BMI Calculator

The BMI Calculator computes body mass index from height and weight, classifies the result using adult BMI bands, and estimates the weight range corresponding to BMI 18.5 through 24.9 at that height. Metric and imperial inputs are supported.

Formula

After converting the inputs to kilograms and metres:

$\text{BMI}=\frac{\text{Weight in kg}}{\text{Height in metres}^2}$

The module classifies adults as underweight below 18.5, normal weight from 18.5 to below 25, overweight from 25 to below 30, and obesity classes above that range. It also reports BMI Prime (BMI / 25) and the ponderal index.

Worked example

For 70 kg and 1.75 m:

1. Height squared: 1.75 x 1.75 = 3.0625.
2. BMI: 70 / 3.0625 = 22.9 after rounding.
3. The BMI 18.5-24.9 weight range at 1.75 m is approximately 56.7 to 76.3 kg.

Questions

Does BMI measure body fat directly?

No. BMI is a weight-to-height index and cannot distinguish fat, muscle, bone, age, or fat distribution.

Is the healthy range valid for children or pregnancy?

The adult bands in this calculator are not appropriate for children, teens, pregnancy, or some athletes. Use age- and context-specific clinical guidance.

Why can two people with the same BMI have different health risks?

BMI omits body composition, waist circumference, medical history, fitness, and other risk factors. It is one screening measure, not a diagnosis.

Health notice and limitations

This tool is educational and does not replace a clinician's assessment. It does not diagnose disease or prescribe a target weight, diet, or treatment.