Below is a chart to help you determine your correct shoe size. Sports shoes need to be snug and supportive but not so tight that you will encounter blistering and discomfort. It is best to choose a shoe that is slightly longer than your foot (approximately 1 cm. or 3/8 in.) to prevent injury. During play, your feet will expand through pressure and heat so try on potential new shoes at the end of the day when your feet have expanded to their maximum size. Where possible, use the same socks for trying on shoes as you will use to play your sport.
An easy way to measure your foot size accurately is to stand on a piece of paper and trace (or have someone trace for you) the outline of your foot. You can then use the measurement of this outline to compare against the chart below.
Please bear in mind that feet are dynamic and your foot size can change over time. Many people even have two different sized feet. The chart below should be thought of as a guideline for helping you find the correct size.