Place your feet side by side on a flat surface and place your heels against a straight edge. You should measure both your feet since it is normal that they do not have the exact same size!
Then we suggest to place a ruler next to one foot and then the other. Make sure that the ruler is touching the straight edge that your heels are also touching and then measure the lengths of your feet in millimetres - from the tip of your longest toe to your heels. Be also aware that your longest toe is not always your big toe.
You should measure your shoe size in the afternoon or evening, as your feet swell slightly during the day.
Once you have measured the length of your feet you can check the shoe size table above to find out which UK shoe size or EU shoe size you need.