To determine your Body Mass Index (BMI)
you must know your weight and your height. Watch this video demonstration of a BMI calculation.
A Answers (18)

Mehmet Oz, MD, Cardiology, answeredHelpful? 4 people found this helpful.

Michael Roizen, MD, Internal Medicine, answeredIf you want to calculate your BMI, the formula for doing so is relatively easy:
 Convert your weight in pounds to your weight in kilograms by dividing your weight in pounds by 2.2.
 Convert your height in inches to your height in meters by multiplying your height in inches  not feet  by 0.0254. (If you are 5 feet tall, your height is 60 inches, or 1.52 meters. If you are 6 feet tall, your height is 72 inches, or 1.83 meters.)
 Square your height in meters (that is, multiply your height in meters by itself).
 Divide your weight in kilograms by the number you obtained in the previous step.
Helpful? 4 people found this helpful. 
Honor Society of Nursing (STTI) answered
Determine your weight, in pounds. Divide that number by the square of your height in inches. Multiply by 703. That is your body mass index. If you prefer the metric system, divide your weight in kilograms by height in meters, and you're done.
Helpful? 6 people found this helpful. 
The formula for BMI is in metric units: kilograms per metersquared.
If you don’t want to convert your height and weight to metric, there are multiple calculators on the web to use, or you can use the following nonmetric formula: 704 times (X) pounds of body weight, divided by height in inchessquared.
The same formula is used for adult men and women of any age, but children are graphed on a different chart, and BMI is expressed as a percentile for that age or height.Helpful? 2 people found this helpful. 
Rose Reisman, Nutrition & Dietetics, answeredTo find your body mass index (BMI), multiply your weight in pounds by 705, then divide the result by your height in inches, then divide again by your height. The result is your BMI. Get out your calculator.
For example, a woman weighs 150 pounds and her height is 5 feet 6 inches (66 inches):
150 lb x 705 = 105,750
105,750/66 = 1602
1602/66 = 24 BMI 
Bill Salt, MD, Gastroenterology, answeredYou can determine your body mass index (BMI) with the following formula:
Step 1. Multiply your weight in pounds by 704.5.
Step 2. Multiply your height in inches by your height in inches (this is the square of your height).
Step 3. Divide the answer in Step 1 by the answer in Step 2 to calculate your BMI.
A BMI over 25 is considered overweight. Obesity is defined as a BMI of 31.1 or higher for males and 32.3 or higher for females.Helpful? 1 person found this helpful. 
Alberto Gamboa , NASM Elite Trainer, Fitness, answered
Ideal Weight Calculator (Body Mass Index) is a reliable indicator of your body’s fitness level, and most importantly, your health risk. It works by calculating your weight and height and correlates it to your body fat level. To determine your BMI, you can calculate it by:
BMI = Weight (lbs) / (Height (in) x Height (in)) x 703
To use a calculator to determine your BMI, go to:
http://www.weightlossplans4you.com/idealweightcalculator.html
Helpful? 2 people found this helpful. 
This is the formula we used on the show:
The Body Mass Index (BMI) is a measurement tool that compares your height to your weight and gives you an indication of whether you are overweight, underweight or at a healthy weight for your height.BMI = ( Weight in pounds/ Height in inches x Height in inches.) x 703
OR
BMI= (Weight in kilograms/ Height in meters x Height in meters)

To calculate your Body mass Index (BMI) divide your weight (in pounds) by your height (in inches) x your height (in inches) and then multiply by 703.
For example, if you are 5'5" (65 inches) and weigh 130lbs your BMI woud be:
(130 divided by 65 x 65) x 703 = 21.6
Therefore, a person who is 5'5" tall and weighs 130lbs would have a BMI of 21.6.Helpful? 10 people found this helpful. 
Joane Goodroe, Nursing, answeredBody Mass Index, or BMI, is a reliable indicator of body fatness based on your height and weight, and places you in one of three categories: normal, overweight or obese.
Free BMI App  A new smartphone app from the National Institutes of Health can let your phone tell you. To get the free app, search “My BMI Calculator” on your phone today. 
Brigham and Womens Hospital Team, Administration, answered on behalf of Brigham and Women's HospitalBody mass index, or BMI, is a more accurate measure of overweight than weight alone for both women and men. First you calculate your weight in kilograms (1 kilogram equals 2.2 pounds) and then divide it by your height in meters squared (1 meter equals 39.37 inches). A healthy BMI is less than 25. A BMI of 25 to 29.9 is considered overweight. A BMI of 30 and above is obese, which corresponds, for example, to someone who is 5 feet 6 inches tall and weighs 186 pounds.

Penn Medicine answered
BMI, or Body Mass Index, is a measure of body fat based on height and weight that applies to adult men and women.
To find out your BMI, divide your weight in pounds by your height in inches multiplied by your height in inches. Take that number and multiply it by 703.
= mass(lb) / (height(in))² x 703
A BMI of less than 18.5 is considered “underweight.” A BMI between 18.5 and 24.9 is considered “normal weight.” A BMI of 25 to 29.9 is considered “overweight.” A BMI of 30 or greater is considered “obese.”
Morbid obesity is defined as having a body mass index (BMI) of more than 40. For men that equates to approximately 100 pounds overweight for women, 80 pounds overweight.

Marjorie Nolan Cohn, Nutrition & Dietetics, answered on behalf of Academy of Nutrition and DieteticsBMI stands for body mass Index and is a measure of height to weight. It doesn’t take into consideration age or gender. Therefore is not the most reliable measure for obesity. It is however, and good rule of thumb tool when trying to determine your health risks associated with weight.
BMI Categories:
 Underweight = <18.5
 Normal weight = 18.5–24.9
 Overweight = 25–29.9
 Obesity = BMI of 30 or greater
To calculate your BMI measure your weight in pounds and height in inches; then multply the answer by 703
[Weight / (height x height)] x 703 = BMI
Helpful? 1 person found this helpful. 
RealAge answered
Your weight and height are measured. Then, your weight is converted to kilograms, and your height is converted to meters and then squared. Your BMI is calculated by dividing your body weight (in kilograms) by your height (in meters squared). The resulting number represents your BMI.
Helpful? 1 person found this helpful. 
Discovery Health answered
Body Mass Index can be calculated in the inches and pounds of the English measuring system (common in the United States) or the meters and kilograms of the metric system (common almost everywhere else).
In both cases, determining the result for adults first requires dividing the weight by the square of the height. For metric measurements, nothing else is required. For pounds and inches, the result must be multiplied by 703 to yield the final answer.
Here are examples.
A person who weighs 180 pounds and is 5 feet 8 inches tall has a BMI of 27.4. That's 180 divided by 68 times 68, multiplied by 703.
A person who weighs 99.79 kilograms and is 1.905 meters (190.50 centimeters) tall has a BMI of 27.5. That's 99.79 divided by 190.5 times 190.5.

BMI is calculated with a formula that uses your height and weight. You can either use meters and kilograms, or inches and pounds. Let’s walk through the one that uses inches and pounds.
For inches and pounds the formula is: [weight in lbs. ÷ (height in inches)2] x 703
Divide your weight in pounds by your height in inches squared, and then multiply that answer by 703. For example if someone is 5’5” (65”) and 150 lbs. the calculation would look like the following:
[150/(65)2] x 703 = 24.96Helpful? 1 person found this helpful. 
Eric Olsen, Fitness, answeredYou can calculate your own body mass index using the following formula: your weight in kilograms divided by your height in meters, squared.
This formula is less daunting than it appears. To figure your BMI, follow these steps:
1. Weigh yourself without your clothes. Divide your weight in pounds by 2.2 to get your weight in kilograms. If you weigh 190 pounds:
190 ÷ 2.2 = 86 kilograms.
2. Measure yourself without your shoes. Then divide your height in inches by 39.4 to determine your height in meters. For example, if you are 5 feet 10 inches tall, you are 70 inches tall and your height in meters is
70 ÷ 39.4 = 1.78 meters.
To find the square of your height in meters, multiply this figure by itself:
1.78 x 1.78 = 3.2.
3. Finally, divide the answer to No. 1 by the answer to No. 2:
86 ÷ 3.2 = 26.8.
Your BMI is thus 26.8, or rather too close for comfort to the danger zone.Helpful? 2 people found this helpful. 
Scripps Health answeredBody mass index (BMI) is calculated as a person’s weight in kilograms, divided by height in meters squared. BMI is not perfect  for example, a pro athlete with very high muscle mass may have a high BMI without being overweight  but for the general population, it is a good guideline.