"Choosing the Right Size:

The finished measurements for Hats listed in the patterns may be slightly smaller than those given below, to ensure the fabric is stretched slightly for a snug fit – this is known as ‘negative ease’. The actual difference between the finished size of a Hat compared to the desired size is usually 2 to 3 inches, 5 to 7.5 centimetres, or roughly 12%, - this is the normal amount of negative ease included within Woolly Wormhead knit and crochet Hat patterns."