Free Online BMI Calculator

It gives a measure of body fat based on height and weight measurements.
It does not consider muscle mass, bone density and other factors and therefore not the most accurate and cannot be used as the basis for any changes as such
It is still a useful guideline and can be one of the ways to track body fat.
It is necessary to calculate BMI to have an idea of what is an ideal weight range for your height.

You can calculate your bmi using the common bmi formula for men and women given below.

Adults BMI = (weight)/(height * height) which is kg/m² where kg is weight in kilograms and m² is height in metres

BMI = kg / (100 x cm)² with kg and cm

BMI = kg / (39.37 x in)² with kg and in

BMI = kg / (472.44 x ft)² with kg and feet

With pounds, BMI = (2.2 lb / m²) since 1 kg = 2.2 lbs

It is a rough indicator of body fat based on height and weight.
In most cases, it is useful guide to know of potential health risks and in which category a person falls into.
It can act as an early warning system for those getting into obese, overweight and underweight categories and enables them to take corrective action quickly.
It's a useful tracking metrics to see how a person is progressing on a regular basis.
For those into weight reduction, it gives an indication of when and where to stop.
It is also very simple to determine and compute. It does not require any extensive tests or measurements to be done.

It does not distinguish muscle mass and body fat.
For body builders and athletes with higher muscle mass, the BMI scores may indicate overweight or obese which is not an accurate measure of health risk.
It can be used as one of references among several other metrics and a rough indicator than as an absolute health metric.

A range of 18.5 to 24.9 is considered normal or good.

A BMI Range of 25 to 29.9 falls into 'Overweight' category.
A BMI Range of Above 30 falls into 'Obese' range.

BMI < 18.5 is considered as Underweight

While there are other alternatives, this is still used as a very quick rough guide.

BMI Formula is same.
It has to be applied to normal adults and the range chart may not be accurate for elderly and children.

Relative Fat Mass (RFM)- It uses height and waist circumference to compute the % of body fat.
Waist to Hip Ratio (WHR) - It uses waist to hip ratio to find the fat distribution measure based on male and female.
Body Adiposity Index (BAI) - It uses height and hip measure along with age group and gender and calculates the % of body fat.

Many recent studies indicate that RFM has a more accurate estimate of body fat % than BMI.

Waist to Hip Ratio gives better estimate of fat distribution and more accurate to predict cardio vascular diseases as per different studies and research groups.

Reverse calculate with BMI as 18.9 and BMI as 24.9 and calculate weight for the given height.

BMI = wt in kg / height ² (m²)

wt in kg = BMI * height square ( m²)

Using the same BMI formula , we can compute the weight for different heights based on BMI normal chart range.
If height is 5 feet 9 inches, weight should be in the range 126 lbs - 169 lbs or 56 kgs - 76 kgs.
If height is 5 feet 3 inches, then weight should be in the range of 105 lbs - 141 lbs or 47 kgs - 63 kgs.
if height is 6 feet, then weight should be in the range of 137 lbs - 184 lbs or 61 kgs - 83 kgs
Refer Recommented Height to Weight Reference table above for all combinations.