Hi Kylie,
I like to count from the bottom up,
They are easiest to count on the lateral or poster-lateral chest wall.
I find the last one and make an assumption that it is the 12th rib.
So if there is an anatomical variant and there is a rib missing or an additional one my method is not perfect!
But if I start from the top I think it is much more difficult.
Simply count from the 12th rib up and then follow the rib around until you find the feature you are trying to localise.
I find myself counting ribs when I have found a fracture most commonly.
Occasionally I am asked to guide an intercostal nerve block at a certain level and again i am having to count.
The advantage of using the poster-lateral thorax is that the ribs are nice and bony with no costal cartilage to confuse things.
I find this simple method quite easy and reliable,
Steve.