BMI Calculator

How to use BMI Calculator

1. 1

   Choose your units

   Use the Metric / Imperial switch to pick kilograms and centimetres, or pounds with feet and inches.

2. 2

   Enter your weight and height

   Type your measurements into the labelled boxes. In imperial mode, height is split into separate feet and inches fields.

3. 3

   Read your BMI and category

   Your Body Mass Index appears instantly to one decimal place, with its category — Underweight, Normal, Overweight or Obese.

4. 4

   Interpret it sensibly

   Use the plain-English sentence as a rough guide only. BMI is a screening tool, not a diagnosis — check with a healthcare professional about your health.

Key features

• Works in both metric (kg, cm) and imperial (lb, ft + in) units
• Live BMI as you type — no “calculate” button
• Shows the WHO category: Underweight, Normal, Overweight or Obese
• Plain-English sentence that explains what your number means
• Accurate conversions (1 lb = 0.453592 kg, 1 in = 0.0254 m)
• 100% private and free — runs in your browser, no uploads or sign-up

Frequently asked questions

How is BMI calculated?

BMI is your weight in kilograms divided by the square of your height in metres (kg ÷ m²). For example, 70 kg at 1.75 m is 70 ÷ (1.75 × 1.75) = 22.9. This tool converts imperial measurements to metric automatically before doing the maths.

What is a healthy BMI?

The World Health Organization considers a BMI from 18.5 to 24.9 to be in the healthy (“Normal”) range for most adults. Below 18.5 is Underweight, 25 to 29.9 is Overweight, and 30 or above is Obese.

What is the BMI formula in pounds and inches?

In imperial units the formula is BMI = 703 × weight (lb) ÷ height (in)². The 703 factor converts the result to the same scale as the metric formula. For instance, 154 lb at 69 in is 703 × 154 ÷ (69 × 69) ≈ 22.7. This calculator does the conversion for you.

Is BMI accurate, and what are its limitations?

BMI is a quick, low-cost screening tool, but it is only a rough estimate. It can’t tell muscle from fat, so very muscular people may read as “Overweight” while others with low muscle may read as “Normal” despite high body fat. It also doesn’t account for age, sex, ethnicity or where fat is stored, and it is not a diagnosis.

Does BMI work for children, athletes or older adults?

Not reliably. Children and teens use age- and sex-specific BMI percentiles rather than the adult bands. Athletes with high muscle mass and some older adults with reduced muscle are also poorly served by a single adult cut-off. Treat the result as general information, not a personal assessment.

Is this BMI calculator medical advice?

No. This tool is for general information only. BMI is a population-level screening figure, not a diagnosis, and your result here is not medical advice. For guidance about your weight or health, please consult a doctor or other qualified healthcare professional.

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