Between two sizes, choose the bigger one if your toes have little room and you wear thick socks, and the smaller one for leather or a heel that slips. This tool weighs those signals for you and gives its reason. A width problem is never solved with a longer boot.
When do you size up?
Size up if your toes touch the front or go numb, because your feet swell during a match. Thick socks or an insole take up room too. Going half a size up is fine as long as your heel stays put.
When do you size down?
Size down if the boot is leather, because leather gives with wear. A heel that already lifts is another reason, since a bigger boot makes that worse. With synthetic and knit be careful, as those materials barely stretch.
What if the boot pinches at the sides?
Then the boot is too narrow, not too short. A bigger size mostly makes it longer, so your foot slides. Pick a model with a roomier forefoot instead. Our list of the best football boots for wide feet is a good place to start, and our guide to boots that are too small or too big covers the signs.