Ape Index Calculator

The ape index compares arm length (also called span) to height. It is a quick way of judging whether arms are long, short or average relative to the body and is considered by athletes in disciplines such as climbing, swimming, boxing and basketball.

This calculator will show you your ape index in two ways - as a difference in centimeters and as a ratio. You can also leave one of the three fields blank, and the tool will calculate the corresponding value for you so that you can find out what arm length is required to achieve a desired ape index.

What is the Monkey Index?

The ape index is sometimes called the gorilla index or simply reach. It's a measure of the ratio between arm length and body height. In most humans, there is little difference between arm length and body height. Leonardo da Vinci illustrated this concept in his drawing of the Vitruvian Man, depicting a person with outstretched arms whose arm length was exactly equal to their body height.

If the arm length is longer than the body height then the ape index is positive. If the arm length and body height are equal then the value is neutral or zero. If the arm length is shorter than the body height then the ape index is negative. This index is often used in sports as having a longer arms allows one to reach further, move more water or hit outside of an opponent's range.

Two methods of calculating the Monkey Index:

There are two common definitions and this calculator displays both at the same time so you don't have to choose one or the other. The ratio method divides arm length by height.

If the ratio is greater than 1.0 it means that the arms are long relative to body size, while a ratio below 1.0 indicates short arms. The difference method subtracts arm length from height and is usually expressed in centimeters.

The difference can be positive or negative. A positive number means the arms are longer than the height, zero means the arm length and height are equal, and a negative number means the arms are shorter than the height. The two formulas describe the same body, just using different units of measurement.

Example calculation:

Assume that your height is 175 cm and the length of your arm is 180 cm. The difference method gives:

The proportionality method results in:

Therefore the ape index of this person is +5 cm or approximately 1.03. This means that the arm length is about three percent longer than the body height. In sports where a longer arm length is an advantage, this difference may not be large but it is still a clear advantage.

What is a good ape index?

In most sports a positive ape index is an advantage and the higher the number the better it usually is. This however only applies to a certain extent and abilities also have to be considered. The following table shows rough guidelines for this measure based on actual measured data of athletes.

How to measure arm length?

Stand with your back, buttocks and heels against a wall, both arms extended horizontally at shoulder height making sure that both arms are the same length. A second person should measure from the tip of one middle finger to the tip of the other middle finger in a straight line. It is easier to keep both arms parallel to the floor if you use a wall with a horizontal line (e.g. a brick wall).

Measure your height on the same day by standing up straight against a wall with shoes off and mark it. If you use the same unit for both measurements, then you can determine the ratio more accurately. However, this calculator converts between centimeters, meters, feet, and inches.

Why athletes are emphasizing arm length.

In climbing a longer arm length can make difficult moves easier by allowing the next hold to be reached without having to change foot position. Studies of competitive climbers have shown that average "ape index" is higher than in the general population, but strength, flexibility and technique still play a crucial role in performance.

In swimming a longer wingspan (arm length) allows for more distance per stroke and more water movement. In boxing and mixed martial arts arm length determines the effective striking range which allows athletes to hit opponents from farther away safely. In basketball, wingspan is often a better indicator of defensive ability than height, which is why NBA Combine measurements include wingspan.

Can you change the Monkey Index?

This is highly unlikely. As arm length and height are determined by the skeleton, the "ape index" is mainly genetically determined and becomes largely fixed after growth stops in late teenage years. Genetics, ancestry, gender and age all affect the "ape index". Since you can only improve these other factors, a low or negative "ape index" should never be a reason to give up on any sport.

This calculator is for general information and educational purposes only. The Monkey Index is just one of many small factors that affect athletic performance and should not be used alone to assess fitness.