BMI Calculator
Find your Body Mass Index and WHO weight category from weight and height.
TL;DR — BMI Calculator: A Body Mass Index (BMI) calculator divides weight by height squared to produce a single number used as a rough screening measure for underweight, healthy weight, overweight or obesity. The World Health Organization uses BMI to compare body weight across populations. It does not measure body fat directly and is less reliable for athletes, very tall or very short individuals, and during pregnancy.
What is the BMI Calculator?
A Body Mass Index (BMI) calculator divides weight by height squared to produce a single number used as a rough screening measure for underweight, healthy weight, overweight or obesity. The World Health Organization uses BMI to compare body weight across populations. It does not measure body fat directly and is less reliable for athletes, very tall or very short individuals, and during pregnancy.
How to use the BMI Calculator
- Choose units (metric or imperial).
- Enter weight (kilograms or pounds).
- Enter height (centimetres or feet/inches).
- Read the BMI value and corresponding WHO category.
Formula
BMI = weight(kg) ÷ height(m)² (imperial: 703 × weight(lb) ÷ height(in)²)
Categories — Underweight: < 18.5 · Normal: 18.5–24.9 · Overweight: 25.0–29.9 · Obese: 30.0+
Worked example
A 70 kg person who is 1.75 m tall: BMI = 70 ÷ (1.75 × 1.75) = 22.86 — in the normal range.
Frequently asked questions
What is a healthy BMI?
WHO classifies BMI 18.5–24.9 as normal weight, 25–29.9 as overweight, 30+ as obese, and below 18.5 as underweight.
Is BMI accurate for athletes?
Not always. BMI cannot distinguish muscle from fat, so muscular athletes often show as overweight despite low body fat. Use Cal44's Body Fat Calculator for a fitness-relevant estimate.
Does BMI apply to children?
BMI in children is interpreted using age- and sex-specific percentile charts, not the adult cutoffs. The WHO and CDC publish growth charts for that purpose.
How can I lower my BMI?
Reduce body weight via a sustainable calorie deficit and regular physical activity. Cal44's Calorie Calculator estimates the deficit needed to reach a target.
Is BMI the best measure of health?
No. BMI is a screening tool. Waist circumference, body fat percentage, blood pressure and lab markers are more directly tied to health outcomes.
Should pregnant women use BMI?
BMI is not a reliable measure during pregnancy. Use pre-pregnancy BMI as a baseline and consult a clinician for healthy weight gain ranges.