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How to Calculate Fat and Weight

Fat is necessary for bodily functions, and helps to regulate body temperature. The term body mass index (BMI) estimates one's body fat based upon height and weight. The difficulty with BMI calculation lies in the fact that it is just an estimation, and does not consider things such as the age or the muscular fitness of an individual. Although BMI is a good indicator of overall health, it works best for adults who are not bodybuilders or competitive athletes and not pregnant or breast-feeding women, according to the Columbia University Medical Center.

Things You'll Need

  • Scale
  • Measuring tape
  • Computer
  • Pencil and paper
  • Calculator
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Instructions

  1. Simple BMI Calculation

    • 1

      Weigh yourself on a reliable scale. Make sure that the scale is level on the floor, and step on the scale. You may need to move the scale around to a few different areas of the floor to ensure you are getting an accurate reading.

    • 2

      Measure your body height, and write it down.

    • 3

      Enter your weight and height into the BMI Calculator on the Mayo Clinic website and click the "submit" button. The site will provide you with your results as a percentage and category, as well as instructions on how to maintain or improve your BMI. For example, a 5-foot-6-inch adult weighing 150 pounds has a BMI of 24.2, and falls into the "normal" range. A weakness with the Mayo Clinic simple calculator is that it does not take into account age or gender.

    Complex BMI Calculation for Men

    • 4

      Weigh yourself on a reliable scale, taking the same precautions to get an accurate reading as above. Multiply your weight by 1.082, then add 94.42; record the answer.

    • 5

      Measure your waist around the fullest point and multiply this number by 4.15; record your answer.

    • 6

      Calculate your lean body mass by subtracting the result of the calculation in step 1 from that of the calculation in step 2.

    • 7

      Calculate your body fat weight by subtracting your lean body mass from your total body mass.

    • 8

      Calculate your body fat percentage by multiplying your body fat weight by 100 and then dividing the total number by your total body weight. Compare this number to the BMI Body Fat Chart found at bmi-calculator.net. Essential body fat for men falls between 2 and 4 percent, with athletic men ranging between 6 and 13 percent. Men with percentages higher than 25 percent are considered obese.

    Complex BMI Calculation for Women

    • 9

      Weigh yourself on a reliable scale, taking the same precautions to get an accurate reading as above. Multiply your weight by 0.732; record the answer.

    • 10

      Measure your wrist at the fullest point and multiply this number by 3.14; record the answer.

    • 11

      Measure your waist at the navel and multiply this number by 0.157; record the answer.

    • 12

      Measure your hips at the fullest point and multiply this number by 0.249; record the answer.

    • 13

      Measure your forearm at the fullest point and multiply this number by 0.434; record the answer.

    • 14

      Calculate your lean body mass by adding the measurement from steps 1 and 2 together, then subtract measurement 3, then subtract measurement 4 and add the measurement from step 5.

    • 15

      Calculate your body fat weight by subtracting your lean body mass from your total body weight.

    • 16

      Calculate your fat percentage by multiplying your body fat weight by 100, then dividing that total number by your total body weight. Compare this number to the BMI Body Fat Chart. Essential body fat in women falls between 10 and 12 percent, with athletic women ranging between 14 and 20 percent. Women with percentages higher than 32 percent are considered obese.

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