BMI Calculator — Free Online Tool
Body Mass Index (BMI) is a quick screening number that relates your weight to your height. Enter your measurements below — metric or imperial — to see your BMI and which category it falls into.
What is the BMI Calculator?
BMI was devised in the 1830s as a population statistic, but today it's the world's most common first-pass health screen. You see it on insurance forms, fitness assessments, and doctor visits because it needs only two measurements and correlates reasonably with body-fat levels across large groups.
It has real limits, though. BMI can't tell muscle from fat, so athletes and very muscular people often score “overweight” while being perfectly healthy. It also doesn't account for age, sex, or where fat is carried. Treat your result as a starting point for a conversation with a health professional — not a diagnosis.
How to use this calculator
- Choose Metric (cm/kg) or Imperial (inches/lbs).
- Enter your height and weight.
- Click Calculate BMI to see your score and category.
Formula
Frequently asked questions
What is a healthy BMI?
For most adults, 18.5 to 24.9 is considered the healthy range by the CDC and WHO.
Is BMI accurate for athletes?
Often not — muscle is denser than fat, so muscular people can have a high BMI with low body fat. Waist measurements or body-fat testing give a fuller picture.
Does BMI work for children?
Children use BMI-for-age percentiles instead of adult cutoffs, because healthy BMI changes as kids grow. This calculator uses adult categories.
How can I lower my BMI?
Sustainable diet and activity changes move BMI gradually. Aim for 1–2 pounds per week and talk to a professional before starting.