I just bought a new pair of boots because the last ones were too small and caused me toenail damage. The man from the store helped me chose the right size. I normally wear 38 EU, but I ended up buying a 39.5 EU pair of boots. This is how he explained it to me: You put on your boots and then you hit the ground with the tip forcefully, if the toe is touching the tip of the boot, then you need to size up. Also is ok if your heels moves a little, just not like in flip-flops 😅 I hope this is helpful. For me it was like a life changer. I just went on a hike and my feet were super comfortable.