To measure your foot length, place a sheet of paper on the floor. Place your bare foot on the paper with the heel against the wall. Mark your longest toe on the paper and then measure the length from the wall to this mark. If you intend to wear socks with that footwear, please ensure you measure the foot length wearing these. To measure the width of your foot, mark and measure the foot at its widest point. This is usually just from the bone below the big toe to the bone below the little toe. Then take that measurement, reduce it by 2mm to accommodate for the space between your foot and the pencil, and use that number to work out your shoe width.
Consider also the shape of your feet. Instep, thinness, hammer toes and other characteristics should be considered as you look at the size, width and shape of the shoe.