There are two common types of fiber diameter measurement or gauging

The English Bradford Spinning Count system originated at the time of the first mechanized spinning equipment in the 19th century. It is determined by the number of same yardage yarn hanks that can be spun by one pound of clean wool. The finer the wool, the more yarn hanks that can be created from the pound. With the Bradford method, the higher the number (qty of hanks), the finer the fiber.

The newer Micron Count system is done with using a microscope and actually measuring the fiber. For a general reference, 25,400 microns equals one inch. With the micron method, the lower the number (micron), the finer the fiber.

Another group of general terms that are used for fiber grading is referring to the sheep’s fraction or percentage of Merino. The oldest established sheep breed in the world is the Merino. This breed has somewhat set a standard for fine wool. Most all other fine wool breeds are created by a Merino cross breeding. This method of grading, which is often used at wool shows, will refer to the fleece as a ½ blood or a ¼ blood, etc. This denotes the amount of Merino blood for the wool. This is usually determined by the feel or the hand of the wool and there is no official measurement occurring.

Here are some examples of sheep breeds and their fiber numbers. Keep in mind that this is only a general rule for these breeds and every sheep is unique. Also, many sheep are cross breeds so consistency is difficult.