Ape index calculator

What the ape index is

The ape index puts your arm span in relation to your height. It is given in two ways: as a difference, that is arm span minus height — the result is then in centimetres and can be positive, zero or negative. Or as a ratio, arm span divided by height. With exactly equal measurements that comes to precisely 1.00.

Day to day the difference is more common, because it is easier to picture. Sports science uses the ratio, because it does not depend on whether the measurement was taken in centimetres or inches and can be compared between people of different sizes.

How to measure

For your height, stand without shoes with your back against a wall, heels touching the wall, looking straight ahead. For your arm span, stretch both arms out horizontally without pulling your shoulders forward and measure from fingertip to fingertip. With a second person this is considerably more reliable than alone.

Expect one to two centimetres of imprecision. Because the ape index is the difference between two measurements, both errors add up — a result just above or below zero therefore cannot be told apart from zero.

What the research says

In climbing gyms a long arm span counts as an advantage. The research supports that rule of thumb only weakly — and in part not at all.

Climbers have longer arms on average

In 2011 Tomaszewski and colleagues compared twenty-one Polish competition lead climbers — personal bests between 6b and 8c on the French scale — with 165 untrained students. The climbers’ ape index averaged 1.05, the control group’s 1.02. The climbers’ arm span was around six centimetres greater.

Among climbers, though, it says little

The same study found only a relationship between ape index and climbing level that missed the statistical threshold (r = 0.397; p = 0.083). The authors explain this by the climbers barely differing from each other in ape index — where everyone has similar values, the value cannot explain performance.

In 2013 Magiera and colleagues measured a mean of only 1.01 in thirty advanced climbers. On the role of the ape index in their performance model they state explicitly that it is not conclusively settled; the effect found in their data even points in the opposite direction, which they themselves describe as contentious.

What can be trained weighs far more

The clearest finding comes from Mermier and colleagues in 2000. They studied forty-four climbers of widely differing levels and grouped the measurements into three components: training, body measurements and flexibility. The trainable component explained 58.9 per cent of the differences in climbing performance, flexibility 1.8 per cent — and body measurements 0.3 per cent. Their conclusion: the results do not support the assumption that a climber needs particular body measurements to succeed in sport climbing.

What follows from this

The ape index is an interesting number, but not a filter. It cannot be changed, in the available studies it explains only a small part of the differences in performance, and it says nothing about how far you can get. Anyone who knows their value afterwards knows something about their proportions — and nothing about their climbing potential.

Frequently asked questions

What is a good ape index for climbing?

There is no solid answer to that. In the only study that compares climbers and non-climbers directly, the climbers averaged 1.05 and the untrained control group 1.02. Within the group of climbers, however, the ape index was not related to climbing level to a statistically reliable degree. No particular target value can be derived from this.

Can a negative ape index stop you from climbing?

No. In the study by Mermier and colleagues, the anthropometric component — body measurements such as arm span, leg length and body fat percentage taken together — explained just 0.3 per cent of the differences in climbing performance. The trainable component explained 58.9 per cent. In that analysis, what you train weighs far more heavily than your proportions.

Can the ape index be changed?

No. Arm span and height are skeletal measurements. Once you have stopped growing they can no longer be influenced — neither by training nor by stretching. Differences of one to two centimetres between two measurements are normal and not a sign of change.

How precisely do I need to measure?

At home you will rarely get better than one to two centimetres. Arm span is measured with your back against a wall, arms stretched out horizontally and without pulling your shoulders forward, from fingertip to fingertip. Doing it with a second person is considerably more reliable than alone. Because the ape index is the difference between two measurements, both errors add up.

Ratio or difference — which calculation is the right one?

Both are in common use. The difference of arm span minus height is more intuitive day to day, because the result comes out in centimetres. The ratio of arm span divided by height is independent of the unit of measurement and is therefore what studies report. The calculator shows both.