If you are between two sizes, go up with little toe room and thick socks, and stay down with leather or a heel that already lifts. This tool weighs those signals and gives you a pick with the reason. A width problem is never solved with a longer size.
When do you size up?
Go up if your toes touch the front or go numb, because feet swell during a match. Thick socks or an insole also take up room. A half size up is the usual step, as long as your heel stays down.
When do you stay down?
Stay down if the cleat is leather, because leather gives with wear. A heel that already lifts is another reason, since a bigger cleat makes it worse. Be careful with synthetic and knit uppers, because those barely stretch.
What do the three questions ask?
The tool asks about your toe room today, the material of the cleat and how your heel sits. Toe room and sock thickness push toward the bigger size, while leather and a lifting heel push toward the smaller one. You get a pick with the reasons, so you can judge it yourself.
What if the sides pinch?
Then the cleat is too narrow, not too short. A bigger size mostly makes it longer, and your foot slides. Pick a model with a roomier forefoot instead. The wide soccer cleats guide lists good options, and too small or too big explains how to tell the difference. For conversions between scales, use the size chart tool.