All shoe size are given in UK size. Please view the above for comparison.
If you worried that sizes given might not be that accurate, here are some guides that I found on internet that might help you.
1 - First, lay a piece of paper on the floor & tape the edge of the paper.
2 - Stand on the paper with your larger foot. Normally is the opposite of our writing hand. Meaning if you are left hander, your right foot will be slightly bigger.
3 - Take a pencil to trace the outline of your foot onto the paper.
4 - Draw a straight line at the END of the traced foot, another line on the tip of your LONGEST toe.
5 - Use a centimeter ruler to measure the draw the edge of your leg to measure the width of your leg
6 - The longest length and the widest width of your leg will be the size for your shoe.
View the above shoe size chart for details.
Just a guide for you, hope it helps :)
Boots Measurement Method