It is commonly believed that the height of a person has a linear relation with his head circumference.
If the person is taller, his head circumference would be more and vice versa.
In some cases, the head circumference of a person is also used as a base for finding his height using some formulas.
However, not much is known about the kind of linear relation these 2 measures of our body share. Several research studies have been conducted to assess how the height of a person is linked to the head circumference.
Here is the analysis of these studies to help you get a better idea of how these 2 measures are linked and whether it is possible to find your head circumference based on your height or guess your height based on your head circumference.
We will also discuss the various applications of the linear relation between height and head circumference to help you understand the importance of these body measures.
But before we begin, let us first learn what exactly head circumference means and how to calculate it.
What is a head circumference?
Head circumference refers to the measurement of the length of the circumference of your head measured at the middle of your forehead.
The measurement is usually taken using a flexible tape as it has to be wound around the head. Sometimes, a paper tape is used in infants or even adults, if they have thick hair.
Measurement of the head circumference is of vital importance in babies for the diagnosis of conditions such as macrocephaly and microcephaly.
Microcephaly is characterized by a smaller head circumference. Macrocephaly refers to a disorder marked by an abnormally larger head circumference that is higher than the 97th percentile of the head circumference of the babies of the same age. 
How to measure it?
It is very easy to measure your head circumference using a measuring tape. You can use a soft tape and place its one end at the middle part of your forehead. The part of the head where you place the end of the tape should be the one having the maximum circumference of your head.
Hence, usually, the forehead is chosen as the place where the head circumference is measured. It is usually the largest part of your head around which you like your hat to sit.
The tape should be ideally placed in the middle of the forehead, both from the vertical and horizontal points of view.
This means the tape should not be placed too high closer to the hairline or too low near the nose.
Once you have placed the end of the tape on the forehead correctly, now gently extend the tape to wind it around your head to come back to the same place on your forehead where you had placed the first end.
Note the reading on the other end of the tape where it touches the first end. This value gives the measure of your head circumference.
If you do not have a flexible tape, you may use thread to measure the head circumference.
After you have measured the length of the head circumference, place the thread along the graduations on your ruler or any inflexible measuring tape you have, to find the value of your head circumference.
The threads you use, in this case, should neither be too thick nor too thin. It should also be sturdy enough such that it can be held in your fingers with a good grip. Avoid using a thread that can stretch as it would give the wrong measure of your head circumference.
What is the average for adults?
Studies in the United States have shown that the average head circumference of adults is around 55 cm or 21 3⁄4 inches in women and 57 cm or 22 1⁄2 inches in men.
Another research that was conducted in the UK has shown slightly different results with the average head size in women being approximately 55.2 cm and the average head size in men being 57.2 cm. 
The head circumference is also slightly different in Australia due to the different race and ethnicity mix in this country. It has been found that the average head circumference is 57 cm in women and 58 cm in men.
The measurement of the head circumference tends to vary among adult men and women of different countries to some extent due to the changes in the physical characteristics of the people belonging to different religions or ethnicities.
Geographical characteristics are also believed to affect the physical features of people due to which their height and head circumference can vary.
These changes in the head circumference of people across the world could be attributed to the changes in their heights. The head circumference is proportional to the height of a person. Hence, in countries where the average height of men and women is more, the head circumference of these people is also likely to be higher.
What is a normal head circumference of a baby?
In adults, the linear relation between the height and head circumference can provide a way to find the measure of one body part when the other is known.
However, in kids, the application of head circumference is beyond just using it for calculating the height.
You must have noticed that the doctors often check the head circumference of a child as a part of the routine examination. The higher or lower than the normal head circumference of a child could be an indication of an underlying illness.
The average head circumference of newborn babies is about 13 3⁄4 inches or 35 cm. The head circumference tends to increase to about 15 inches or 38 cm by the age of one month.
The height, as well as the head circumference of boys, tend to be slightly higher than that of girls. The average difference between the head circumference of girls and boys below the age of one month is less than 1⁄2 inch or 1 cm.
Checking the head circumference of the baby helps the doctors in the early diagnosis of conditions such as microcephaly and macrocephaly.
The brain and head of babies undergo 80% of their growth during the initial 2 years of their life. By the end of one and a half to two years, the bones in the skull fuse together after which the growth of the head circumference may slow down.
Measuring the head circumference helps doctors to assess the growth of the brain.
The regular measurement of the head circumference and analyzing its relation to the measures of the other body parts can help to evaluate the child’s growth and also allow in the early diagnosis of the conditions that can affect the brain growth.
However, it is sometimes normal for the head size of the baby to appear disproportionate to his or her weight and height.
This may happen because the genetic make-up of a child also plays a role in determining his head circumference and also, its relation to his height.
For example; if one or both the parents of the baby have bigger heads compared to their heights, the baby is likely to have similar features.
Hence, it is the consistent pattern of growth of the head circumference that is considered more important than the size of the child’s head circumference relative to the rest of his body.
As far as the growth of the head circumference is steady, without any rapid change causing an increase or decrease, the child can be considered to be having a healthy growth pattern. 
We have, so far, learned the importance of measuring the head circumference and how it influences the health of a child while helping in the diagnosis of diseases. Now, let us move further to learn how the head circumference is linked to the height and the linear relation that exists between these 2 body measures.
Linear relation between head circumference and height for establishing personal identity
Several studies have been conducted to put to use the linear relation between the height of a person and his head circumference for establishing personal identity.
Establishing personal identity is one of the major concerns in forensic investigations. Forensic anthropology involves the estimation of height when the head circumference is known and vice versa.
The objective of the study was to make an attempt to understand the link between the height and the head circumference of a person in order to derive a regression formula for the estimation of one of these measures using the other.
The study consisted of 440 participants among which 258 were males and 182 were females.
These participants were young with most of them being students between the ages of 17 and 25 years.
The heights and head circumferences of these participants were measured in centimeters. The data was analyzed with the help of statistical software called the SPSS-16.
The findings of this study have revealed that a significant correlation exists between the height and the head circumference in both men and women.
The regression equation for the height and the head circumference was derived as follows:
Y = 1.734 X + 70.36
Y = 0.916 X + 106.8
In both men and women:
Y = 1.648 X + 71.69
Where, X is the head circumference and Y is the height of the individual
This study has revealed that head circumference has a highly significant positive correlation with height. The results of this study could help in the evaluation of the medico-legal cases by allowing forensic experts to establish the identity of a person. These findings will also be useful for anthropologists and anatomists. 
The association between height, weight, and head
While there have been several ways to know the height of a person based on the head circumference, the applicability of these formulas may not always provide perfect results.
Hence, an attempt was made to assess and reconsider the accuracy of the linear relation between the head circumference and height to ensure there are no discrepancies in the results when this relation is put to use for medical and forensic purposes.
Let us have a look at the findings of the study that was aimed at re-assessing the linear link between head circumference and height.
Under normal health and nutritional conditions, the body height, head circumference, and weight of a person are significantly co-related. It is hypothesized that the apparent association between the weight, head circumference, and height of a growing child could be misleading.
This study involved the reanalysis of the data of 7,375 girls and 7,444 boys whose heights and head circumferences were measured in the East-Germany when they were of the age of 0 to 7 years.
The measurements of the body height/length, leg length, biacromial shoulder breadth, sitting height, thoracic depth, thoracic breadth, thoracic circumference, head volume, body weight, hip skinfold vertical, and percentage of body fat were taken using the method of principal component analysis.
The results of this study have revealed that a strong association exists between the skeletal growth, head volume increments, and fat accumulation.
Yet, despite this proportionality, the skeletal growth, head growth, and fat acquisition may, at times, exhibit a different pattern.
There are 3 components that can explain nearly 60% to more than 75% of the cumulative variation between these measures of the body parts in babies at birth and later, at the age of 7 years.
The parameters of skeletal growth have been predominantly found to load on the 1st component that is clearly separated from the indicator of fat deposition. After the age of 2 years, the head volume tends to load on a separate 3rd component in both girls and boys indicating the independence of the growth of the head in relation to height and body weight.
This study has concluded that even under appropriate health and nutritional circumstances, the nutritional status, head circumference, and body size may not always be co-related. 
The findings of this study have raised doubts over the applicability of the use of head circumference for finding the height of a person.
Yet, it can be assumed, with a certain level of accuracy, that linear correlation does exist between height and head circumference, though the exact formula for the derivation of each of them when the other is known needs to be refined.
Further studies might be needed to understand the relation between the height and head circumference.
There is also a need to evaluate how the factors influencing the height of a child such as genetics and nutrition can also impact the growth of the head. Careful evaluation of these factors is expected to provide a better understanding of the link between these 2 body measures allowing us to arrive at a more accurate formula or linear equation linking both.
The application of head circumference measurement in the medical field
Microcephaly is one of the common conditions that can be diagnosed based on the abnormities in the head circumference of a child.
Your doctor can measure the baby’s growth in several ways and measuring the head circumference is one of them. 
Comparing the rate of increase or growth of the head circumference to the rate of increase in the height of the child can help the doctors in the early diagnose of some diseases. For example; if the baby’s brain is not growing properly, he may be suffering from a condition called microcephaly.
Microcephaly refers to a developmental disorder that causes the baby’s head to be smaller than those of the other kids of the same age and gender. This condition may be present when the baby is born.
Microcephaly usually develops in the initial 2 years of life. Though currently there is no cure for this condition, early diagnosis, with the help of regular measurement of the head circumference, followed by an appropriate treatment might improve the child’s prognosis.
Let us have a look at the common causes of microcephaly and why it is important to diagnose this condition at an earlier stage.
What are the common causes of microcephaly?
In most cases, microcephaly occurs due to abnormal brain development. The abnormality in the brain development may begin while the child was still in the mother’s womb or later, during infancy.
The cause of abnormal brain development could be linked to a complex interplay between genetic and environmental conditions.
Genetic conditions that are known to cause microcephaly include:
- Cornelia de Lange syndrome that slows down the child’s growth both inside and outside of the mother’s womb. The common characteristics of this condition include arm abnormalities, intellectual problems, and distinct facial features.
For example, children with this disorder may have eyebrows growing together in the middle, a smaller nose and teeth, and low-set ears.
- Down syndrome, also called trisomy 21, is another common cause of microcephaly. It is characterized by symptoms like cognitive delays, intellectual disability, extreme weakness of the muscles, and distinctive facial features like a round face, almond-shaped eyes, and small features.
- Children with a Cri-du-chat syndrome have a distinctly shrill or a high-pitched cry, such as that of a cat. The common characteristics of this syndrome include low birth weight, intellectual disability, weak muscles, and facial features like wide-set eyes, low-set ears, and a small jaw.
Other than these genetic causes, microcephaly may also occur due to the exposure of the child to certain viruses, toxins, or drugs while in the womb. 
The use of alcohol and some drugs by the mother during pregnancy may trigger the development of microcephaly in children.
It can also occur due to certain complications during childbirth. The reduced oxygen levels in the baby’s brain during labor may increase the risk of developing this condition. Severe maternal malnutrition is also one of the factors that can increase the risk of developing it.
Children diagnosed with microcephaly often develop mild to severe complications, especially if the condition is detected at a later stage.
Kids with mild complications usually have normal intelligence, though their head circumference would be smaller for their age and gender.
Children with more serious complications may experience delayed motor functions, intellectual disabilities, delayed speech, hyperactivity, seizures, facial distortions, and difficulties with maintaining balance and coordination.
This is why; it is important to measure the head circumference of a child and ensure it is in proportion to his height based on the age and gender to help in the early diagnosis of microcephaly.
It is possible to find the head circumference of a person when his height is known and vice versa with reasonable accuracy.
The results may have a marginal error due to the influence of certain factors that affect the growth of the height and head in different ways.
However, the formula we discussed above can help us arrive at a fair estimation of the measures of these body parts.
Being aware of the proportional relation between head circumference and height could help physicians in the early diagnosis of certain diseases. It would also help forensic experts in their investigations of medicolegal cases.