Climbers call the difference between your arm length and your height your 'Ape Index'. The difference is normally expressed in inches. So if your arm span is three inches wider than your height, then that gives you an ape index of +3. If your arm span is 2 inches smaller than your height, that gives an ape index of -2.

It's very easy to quickly find your ape index, just stretch up against a wall or post and mark how high you can reach (that's your arm span) then keeping your top finger in place, stand up and compare it to your height. You don't have to be too precise with this, you can look at the difference and estimate it in inches.

We can see below that Paul has an ape index of +3 :