Try on shoes at a local store to determine UK shoe size, if ordering Irish dancing shoes online. When you find a pair that fits you well, look at the box to determine what size it would be in the UK. Most shoe boxes will list the UK size. This will be the size you want to look for when ordering shoes online.
Locate shoes that are the correct UK size. A youth American shoe size 11 to 13.5 will equal a UK shoe size of 11.5 to 13.5. A size 1 or 1.5 will not be any different in UK sizing. A shoe size of 2 to 4 will go down about one full size. Ladies' shoes sizes 4.5 to 11 will go down roughly 1.5 to 2 shoe sizes.
Purchase shoes that will fit snugly. They will stretch when worn, by about 1/2 inch. Do not purchase shoes that are uncomfortably snug. Children should be bought shoes about a half size too big, to allow room to grow. This may mean they are a bit too big upon purchase, so use your best judgment.