Easy Converter

BMI Calculator

Compute your Body Mass Index (BMI) in metric or imperial units and see which WHO category you fall into. The calculator displays the formula, your numerical result, the official cut-offs and a brief explanation of the limitations of BMI as a single health metric.

How to use

  1. 1

    Pick units

    Choose metric (kg, cm) or imperial (lb, ft/in).

  2. 2

    Enter weight and height

    Type your values. The result updates live.

  3. 3

    Read your BMI and category

    The calculator shows your BMI, the WHO category and the cut-off chart.

Technical details

BMI was introduced by the Belgian statistician Adolphe Quetelet in the 1830s as a population-level proxy for adiposity. It is defined as `BMI = weight (kg) / height² (m)`. The WHO categorises adults using fixed cut-offs: <18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, ≥30 obese.

BMI is a powerful epidemiological tool because it correlates well with body fat across large populations and is trivial to measure. It is a poor individual diagnostic because muscle mass, bone density and fat distribution all affect health independently — many athletes register as overweight while having very low body fat.

For more accurate body composition analysis, combine BMI with waist circumference (a proxy for visceral fat), body fat percentage (DEXA or bioimpedance), and fitness markers (VO2max, grip strength). BMI on its own should be considered a screening tool, not a diagnosis.

For imperial units the formula is `BMI = 703 × weight (lb) / height (in)²`. The calculator handles both systems and displays the result alongside the WHO classification chart.

Frequently asked questions

Is BMI accurate?
It is a useful screening tool for populations but a rough individual indicator. Combine with waist circumference and body fat % for a complete picture.
Does BMI apply to children?
Children use age- and sex-specific percentile charts, not adult cut-offs. The calculator targets adults aged 18+.
Why does my athletic friend register as overweight?
Muscle weighs more than fat. BMI cannot distinguish between the two — that is its main limitation.
What is a healthy BMI range?
WHO defines 18.5–24.9 as normal for adults. Asian populations sometimes use a lower upper bound (23) due to higher metabolic risk at the same BMI.
Is my data saved?
No. The calculator runs locally and stores nothing.
Reviewed by:Easy Converter Engineering Team

This tool was tested and calibrated by our engineering team. All processing happens locally in your browser — your files and data never leave your device.