Trying to figure out how tall your child will be as an adult is one of the fun games of parenthood. If one of you is short and one is tall, you might wonder if your child will end up somewhere in the middle or will take after one or the other of you. As long as your spouse is the biological parent of your child, his height will have an impact on how tall your child will be, since he contributes half the genetic material to your child. However, environmental factors can also influence height.
Every human being -- your child included -- inherits half his genetic characteristics from each biological parent. Genes for certain characteristics, including eye color, have been easier to identify than those for height. Genetics accounts for around 60 to 80 percent of height potential, reports molecular biologist Chao-Qiang Lai of the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University in the December 2006 issue of "Scientific American." That means you and your partner each influence between 30 to 40 percent of your child's height.
Height is one of the more complex genetically inherited traits because as many as 20 genes -- if not more -- interact to determine your child's height. Geneticists have found genes for height on the 7th, 8th and 20th chromosomes, as well as on the X chromosome, which is the female sex chromosome, according to the Standford School of Medicine Department of Genetics. Because so many variables can affect height, having a tall spouse doesn't guarantee you'll have a tall son or daughter, but it does increase the odds.
Your child's environment determines around 20 to 40 percent of his adult height. People of Japanese descent are getting taller, because their diet now includes more protein than it once did. Although Japanese people might always have had the genetic potential to reach a certain height, consuming a diet low in protein and high in carbohydrates may have prevented them from reaching their potential. Illness can also affect whether or not your child reaches his full height potential. Your behavior during pregnancy or illnesses that develop while you're pregnant can also affect your baby's growth even if he inherits tall genes from his dad. Smoking, for example, can affect fetal height and weight as well as growth later in life.
Multiplying your child's height around age 2 will give you a rough idea of how tall he will eventually be, but it's only an estimate. Boys may be slightly taller and girls slightly shorter. Health problems or diet before or after age 2 could result in his not reaching his optimal height or in his growing taller than it first seemed he would at age 2. Another rough method of determining your child's adult height is to add both biological parents' height in inches together. Then add 5 inches for boys and subtract 5 inches for girls; divide the total by two. For example, if you're 60 inches and your spouse is 70 inches, 60+70=130. If you have a son, add 5 inches. 130+5=135. Divide by 2= 67 1/2 inches, or 5 feet 7 1/2 inches tall. Your son will be within 4 inches of that height, in most cases, MayoClinic.com explains.