ZeroFee Tools
Free BMI calculator with WHO body mass index categories and healthy weight range

ZeroFee Tools' free BMI calculator is an online body mass index calculator that tells you whether your weight is in a healthy range for your height. Enter your height and weight in metric or imperial units to get your BMI instantly, see your WHO category on a color scale, and find the healthy weight range for your height.

Calculate your BMI

Note: This calculator provides estimates for information only and is not medical advice. BMI is a screening measure; talk to a doctor or qualified health professional about your weight and health.

Frequently asked questions

What is a good BMI number?

For most adults, a BMI between 18.5 and 24.9 is considered healthy by the World Health Organization. The single "best" number inside that range varies with muscle mass, frame size and age.

How is BMI calculated from kg and cm?

Divide your weight in kilograms by your height in meters squared. With cm, first convert: BMI = weight(kg) / (height(cm)/100)^2. The calculator handles the conversion for you.

Can BMI tell body fat percentage?

No. BMI is a weight-to-height ratio, not a body composition measure. Two people with the same BMI can have very different body fat percentages, which is why athletes often pair it with a body fat estimate.

Is this BMI calculator suitable for children?

No. Children and teens need age-and-sex-specific BMI percentiles, not adult cutoffs. This tool uses adult WHO categories for ages 20 and up.

How often should I check my BMI?

Monthly is plenty. Weight fluctuates daily with water, food and hormones; monthly checks reveal the real trend without the noise.

What is BMI and how is it calculated?

Short answer: BMI (body mass index) is a screening measure of body fat based on height and weight. The formula is weight in kilograms divided by height in meters squared (kg/m2). For imperial units, multiply weight in pounds by 703, then divide by height in inches squared.

Example: a person who is 70 kg and 1.75 m tall has a BMI of 70 / (1.75 x 1.75) = 22.9, which falls in the healthy range. Our calculator does this math instantly in either unit system and places your result on the WHO category scale.

What is a healthy BMI range for adults?

Short answer: The World Health Organization defines a healthy BMI as 18.5 to 24.9 for adults aged 20 and over. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is classified as obesity, split into classes I, II and III.

These cutoffs are population guidelines, not personal diagnoses. Your healthy weight range shown above is simply your height plugged into the 18.5 and 24.9 boundaries. Muscle mass, bone density, age and pregnancy all affect what a healthy weight means for you.

Is BMI accurate for athletes and muscular people?

Short answer: Not always. BMI cannot tell muscle from fat, so very muscular people, athletes and bodybuilders can land in the "overweight" range while having low body fat. For a fuller picture, pair your BMI with a body fat percentage estimate.

Older adults may also read "healthy" while carrying excess fat with low muscle (sarcopenic obesity). If your BMI surprises you, our body fat calculator gives a complementary estimate from simple tape measurements.

How to use this calculator step by step

  1. Choose metric (cm/kg) or imperial (ft/in/lbs) units with the toggle.
  2. Enter your height and weight in the fields.
  3. Click "Calculate BMI" to see your result instantly.
  4. Read your WHO category on the color scale and note your healthy weight range.
  5. Recheck monthly to track trends rather than day-to-day noise.

You may also need

Calorie CalculatorGet daily calorie targets matched to your BMI goal. Body Fat CalculatorBMI can't see muscle vs fat - measure body fat % instead. Age CalculatorAdult BMI categories apply from age 20 - check yours.