We have checked and tightened the girth, next we need to adjust the stirrups before we get on. As mentioned earlier whilst leading the horse or whilst resting in the loose box the stirrups are stored in the 'run up' position.
The stirrup is pushed up the side of the stirrup leather lying next to the saddle whilst the excess is then pulled through the stirrup and hangs down. In this position the stirrup is quite secure until you pull it back.
To get a rough idea of how long the leathers should be for you adjust their length so that when the stirrup iron reaches your armpit you can just reach the stirrup bar.
After adjustment always make sure the stirrup buckle is pulled up to the top of the stirrup bar else it will stick out and rub your leg something terrible.
Taken From New Rider