You might see suggestions to size up or size down from your regular shoe size when buying work boots. Of course, if the recommendation comes from the manufacturer, you should listen. However, in general, you should buy work boots in the same size as regular shoes.   You can tell that a particular boot fits you correctly if it holds your ankle firmly in place, your toes have about a thumb's width of space to move, and your feet don't slide around inside the shoe when you walk.