BMI Calculator

Calculate adult body mass index (BMI) from weight in kilograms and height in centimetres. The result is a screening measure that relates weight to height. This page uses adult categories for people aged 20 or older; it is not a child growth-chart calculator.

How the calculation works

BMI equals weight in kilograms divided by height in metres squared. For the displayed adult categories, below 18.5 is underweight, 18.5 to below 25 is the healthy-weight category, 25 to below 30 is overweight and 30 or above is the obesity category.

Worked example

At 70 kg and 175 cm, BMI is 70 ÷ 1.75² = 22.86 kg/m². That falls within the adult healthy-weight category used here. Changing the height or weight changes the result; age is not part of this adult arithmetic formula.

Enter measurements consistently

Use kilograms and centimetres in this form. If your record is in pounds or feet and inches, convert it before entering the numbers. Measure height without shoes and use a reasonably current weight so the result represents the same point in time.

What to do with a screening result

Treat the category as one piece of information. Discuss concerns with a qualified health professional who can consider other measurements and history. A healthy-weight BMI category does not guarantee health, and a value outside it should not be used as a personal judgement.

Important limitations

BMI does not directly measure body fat or distinguish muscle from fat. Pregnancy, body composition and individual health context can change its usefulness. Adult cutoffs should not be applied to children or teenagers, who require age- and sex-specific interpretation. A result does not diagnose health or prescribe weight loss.

Frequently asked questions

Is BMI a body-fat percentage?

No. BMI is weight divided by height squared.

Can children use these categories?

No. Children and teenagers need age- and sex-specific growth-chart interpretation.

Reference

CDC adult BMI calculator. The method and limitations above identify what this page does and does not infer from that reference.