Having a larger arm span is often considered an advantage for sportsperson and even warriors.
In earlier times, a warrior who had a larger arm span was believed to have a natural advantage over those with shorter arm spans, especially during one-to-one combat with spears or swords.
Luckily, the times have changed.
But even today, having a longer arm span is considered an advantage, though the reasons are different.
Several studies have been conducted to assess how the arm span correlates with the height of a person.
Research is also being conducted to assess whether the change in the ratio of height to arm span could be an indication of any disease. These studies have been conducted with a focus on assessing the change in the arm span with respect to the change in the height as a result of genetic anomalies.
If you are curious to know the correlation between height and the arm span of a person, keep reading. We will discuss what arm span exactly means, how to measures it, and how the height to arm span ratio helps in the diagnosis of some diseases.
What is the arm span?
The arm span refers to the measurement of the total length of the hands when they are extended in opposite directions on both the sides of the chest.
The arm span is measured from the fingertips of one hand to another. It is also called the wingspan or ‘reach’, possibly because it also helps to determine the ability of a person to reach an object by only extending his hand.
The longer the arm span, the bigger will be the length of his hands, and hence, the larger will be the reach!
The best way to measure the arm span is to stand straight with both your arms raised along the sides of your body at the shoulder such that they are parallel to the ground.
Many people are not aware that the arm span provides a fairly accurate measurement of the height of a person.
The length of the arm span is often very close to the height. Hence, the arm span is commonly used as a way to find the height of people, especially when their heights can not be measured using conventional methods such as standing against the wall.
Similarly, the height of a person can be used to get an idea of the length of his arm span.
This suggests that the arm span and height of a person are directly linked. If a person has a shorter arm span, his stature will be shorter while a person with a longer arm span is likely to be taller.
For example, the arm span of a man with a height of about 5 feet 10 inches or 178 cm will be around the same length.
So, it can be said that the height to arm span ratio is usually 1:1. 
What are the uses of the height to arm span ratio?
Measuring the arm span of an adult or child can help to get insights into some of his or her health issues and the risk of diseases. It also provides a way to assess the possibility of having any genetic disorder that could affect the growth and development of the bones.
The diagnosis of certain genetic disorders can be based on the abnormal ratio between the height and the arm span. An accurate measurement of both the height and the arm span is essential to be able to calculate this ratio.
Read on to learn the right ways to measure your arm span so that you can apply it for the diagnosis of diseases and the assessment of your growth and development.
How to measure your arm span?
Most men and women are able to measure their arm span easily by following the simple steps given below.
While it is easier to measure the length of our arms on our own, it is difficult to measure our arm span by ourselves. Hence, it would be good to have someone help you measure your arm span accurately.
Let’s check how you can measure your arm span with the help of someone.
- Position yourself to get an accurate measurement of your arm span. Stand upright against the wall making sure your back is in contact with it as much as possible. Stand straight to your fullest height to allow your partner to take the reading easily and more accurately.
- Avoid slouching as it may shorten your arm span leading to wrong measurements.
- If you are experiencing difficulties in standing against the wall, you may stand at any place, but as straight as possible while avoiding hunching of the shoulders.
- Stretch out the arms along both sides of the body as far as they can go. Avoid bending your fingers or arms. Try to maintain the arms level or parallel to the floor such that the entire length of your hands from the fingertips of one hand to the fingertips of another hand across the chest forms a single straight line.
- Raising or lowering of the arm on any side may decrease the measurement of the full arm span.
- Now, ask your partner to use a measuring tape to measure the length from the tip of the middle finger of your left hand to the tip of the middle finger of your right hand to get the length of your arm span.
You can now compare the length of your arm span with your height. The heights of most people are about equal to their arm spans, though a minimal difference of a few centimeters or inches may exist.
You can measure your height yourself or ask your partner to measure it and compare the 2 lengths to find the height to arm span ratio.
This is an easier method to measure your arm span. However, in some cases, it may be difficult for a person to stand straight due to conditions such as extreme weakness and disabilities arising out of musculoskeletal diseases or genetic abnormalities.
In such cases, it is advisable to calculate the arm span after taking separate measurements of different components of the same.
Here is an alternative method you can try to measure the arm span of a person in whom the earlier method can be difficult to follow.
- Determine the components of the arm span.
The arm span comprises the lengths of the arms measured from the tips of the middle fingers to the shoulder and the breadth of the chest between the two shoulders. You can measure these components separately to calculate the arm span.
- Calculating the arm lengths
Let the person sit straight or lie down on a flat surface or a bed with his arms relaxed and placed at the sides. If the person is sitting, make sure he is not hunching or leaning forward, as it may lead to incorrect measurements of the arm lengths.
Keep the arms of the person fully relaxed with the fingers gently stretched parallel to each other (and not in a fanning manner). Make sure the person feels comfortable in the position. There should not be any stretching or pulling of the muscles or bones as it may result in pain and stiffness later.
Now, place one end of a measuring tape at the bony prominence of the left shoulder. This is the approximate location from where the hands begin.
Extend the tape to the tip of the middle finger of the same side. This length gives you the measurement of the left hand.
Now, repeat the same on the right side to get the measurement of the right hand from the shoulder to the tip of the middle finger.
- Measurements of the chest breadth
Now, the next step is to measure the length of the chest from one shoulder to another. You can ask the person to sit or lie down on his abdomen for this measurement.
Make sure the person feels comfortable while lying on his belly. The pillow should be removed and the person should lie with his nose gently touching the bed keeping the neck straight. Turning the head to the sides should be avoided.
Ask the person to keep his shoulder relaxed so that the chest and shoulders form a straight line without any bending or curving.
Making the back or shoulder muscles stiff while lying on the belly may cause the back to be curved leading to an inaccurate measurement of the arm span. Hence, the length of the chest from one shoulder to another should form a straight line.
Now, hold one end of the measuring tape at the same bony prominence on the left shoulder joint where you had placed the tape while measuring the length of the left hand. Measure the breadth of the chest until the right shoulder by extending the tape to the bony prominence of the right shoulder.
This length gives the measure of the chest length between two shoulders.
- Calculating the arm span
Now, you can add the lengths of both the hands and the breadth of the chest to get the measurement of the arm span.
While this method gives a fair idea of the length of the arm span, the measurement may not be accurate. Hence, it is preferable to try the first method, whenever possible.
The method of measuring the arm span in the sitting or lying down position should be reserved only for patients who are unable to stand.
The correlation between your arm span and height
As discussed earlier, the height to arm span ratio is nearly 1:1 as the length of the arm span often equals the height of a person.
This is why; the height of a person is often taken into consideration while calculating his arm span and vice versa.
Here is an interesting method to check the correlation between height and arm span.
- Stand straight against a wall such that your back is in contact with the wall as much as possible. It is the same position that you stand in while measuring your height.
- Now, hold the middle finger of your right or left hand at a place where the top of your head touches the wall.
- Move away from the wall slowly without losing the contact of the finger to the spot.
- Now, keeping the tip of the middle finger still held against the spot, bend slowly to touch the ground with the tip of the middle finger of your other hand. The place on the ground should be the same as where your heels were touching while in the standing position.
You will be surprised to find that your height, which is the distance between the top of your head and the floor – where you are now holding the fingers of both the hands – is perfectly covered by your arm span.
When you stretch your hands to touch both the spots – the first spot where the top of your head touches the wall and the second spot at the base of the wall – you are actually covering the distance of your arm span.
This small experiment proves that the length of the arm span is nearly equal to the height of a person.
It also suggests that if you are taller, your arm span will be longer and vice versa.
However, in some cases, the measurement of the height and arm span may not match exactly.
Several factors including the age and gender of a person can influence the ratio between his height and arm span. 
Here is a brief discussion about the application of arm span for the diagnosis of certain diseases and conditions that may alter the height to arm span ratio.
The application of the height to arm span ratio
Since the arm span provides a fairly accurate estimation of any person’s height, it is commonly used as a reference for the measurement of the height in people who cannot stand on the traditional stadiometer or against a wall due to musculoskeletal and neurological abnormalities affecting their spine or legs.
In patients who suffer from osteoporosis, lordosis, scoliosis, or kyphosis and those who have had an amputation of the leg, the arm span may be used to know their heights.
Arm span can also be used to find the height of people who are confined to a bed or wheelchair. 
Interestingly, arms span may also be used as an indicator of the pulmonary functions in critical patients.
One research study has revealed that the arm span can provide an alternative method for finding the height of patients with severe breathing difficulties and pulmonary diseases.
Measuring the arm span in these patients can help in the interpretation of the pulmonary function tests based on the assessment of the normal values. These normal values are derived from certain equations created with the help of the measurements of arm spans, heights, and pulmonary function tests in people without any deformity or serious pulmonary disease. 
However, in some cases, the arm span of a person may not be the same as his or her height.
Certain conditions can reduce or increase the height or arm span such that they are no longer in the ratio of 1:1. In such cases, the higher or lower height to arm span ratio may be used for the diagnosis of the underlying abnormality.
Here are some conditions that may cause variations in the height-to-arm span ratio.
Diseases responsible for the variations in the height to arm span ratio
Patients who suffer from disorders that affect their growth causing them to be shorter or taller in height may have an abnormal height to arm span ratio.
For example; patients who suffer from excessive growth hormone secretion may have their height a bit longer than their arm span.
It should be noted that the increase in the secretion of growth hormone in these patients can lead to a faster growth in the height as well as the arm span. However, the increase in arm span may not always be the same as the increase in the height due to which the height to arm span ratio could be lower or higher than 1:1.
Similarly, a smaller height to arm span ratio may occur in adult patients who suffer from diseases that cause the vertical loss of height.
For example; as age advances, the vertebral bodies in the backbone are subjected to degenerative changes. As a result, the rate of degeneration of the bone tissue excessed its rate of regeneration due to which the bones begin to lose their mass causing them to collapse on each other.
The reduced length of the vertebral column due to these degenerative changes may reduce the height of the person, though his arm span may remain the same.
Hence, the 1:1 height to arm span ratio can not be applied to calculate the height in these patients.
Moreover, the osteoporotic changes occurring in the bones due to aging in men and women and the hormonal imbalances occurring in the menopausal women also contribute to similar changes.
As age increases, the bones begin to lose their minerals. The loss of bone mineral density is faster in women due to the decline in the production of estrogen during and after menopause.
This is another reason why the height of a person may reduce as a result of aging.
These are some reasons why the height to arm span ratio may not be applicable in all cases.
Nevertheless, even in such cases, measuring the height and arm span of the patient can help to assess the severity of the conditions.
It can provide a measurement of the loss of height as determined by subtracting the present height of the patient from the length of his arm span. The larger the difference between the height and arm span, the higher would be the loss of height.
Diagnosis of genetic anomalies based on the arm span
The diagnosis of genetic anomalies can be based on the arm span of the person as most genetic disorders affect the height of the person more severely than his or her arm span.
Some genetic disorders do not influence the growth of the arm bones due to which the patient’s arm span may remain unaffected, though he may grow to be taller or shorter depending on the condition he is suffering from.
For example; generic abnormalities like Marfan syndrome may lead to faster growth of the long bones in the legs due to which the height of the child may be comparatively longer than his arm span.  
Similarly, genetic disorders like Down syndrome may cause a defect in the growth of the long bones and cartilage resulting in shorter stature. However, these conditions may not affect the growth of the bones in the hands with equal severity.
Hence, patients with Down syndrome usually have a shorter stature with a shorter arm span though their height may still be lesser than their arm span. So, their height to arm span ratio would be lower than 1:1. 
Arm span provides a reliable indicator for measuring the height of a person. The height to arm span ratio can be used for assessing the loss of height due to various conditions. It can also be used for the diagnosis of genetic or musculoskeletal abnormalities.