What is the ape index?
The ape index compares your arm span (wingspan), fingertip to fingertip with arms stretched out, with your height.
How to calculate the ape index
It is written two ways (Wikipedia):
- Difference: arm span − height. 180 cm span and 175 cm height gives +5 cm.
- Ratio: arm span ÷ height, also called the wingspan to height ratio. The same example gives 1.029.
A ratio of 1, arm span equal to height, is the classic proportion described by Vitruvius and drawn in Leonardo da Vinci’s Vitruvian Man. Most people are within a few centimetres of it.
How to measure your arm span
- Stand with your back against a wall, feet together, barefoot.
- Raise both arms sideways to shoulder height, palms facing forward, fingers straight.
- Have someone mark the tips of your middle fingers on the wall, then measure between the marks.
- Measure your height barefoot in the same session, back against the wall, looking straight ahead.
Does it matter for sport?
Longer arms help reach, so a positive index is common among swimmers and basketball players; the average NBA player’s ratio is about 1.06. In climbing the evidence is mixed: some of the best climbers have negative indices. In MMA, research found the index cannot predict who wins a bout (Wikipedia).
How limb lengthening changes your ape index
Lengthening the femur or tibia adds height but leaves your arms unchanged, so your ape index drops by exactly the height gained. Someone with +3 cm who gains 6 cm ends up at −3 cm. Whether anyone notices depends on where you start; arms that end up well short of your height may look short next to longer legs. See how your whole body changes in the limb lengthening simulator, and check your leg proportions with the femur to tibia ratio.