Wool classing is the production of uniform, predictable, low-risk lines of wool, carried out by examining the characteristics of the wool in its raw state and classing (grading) it accordingly. Wool classing is done by a wool classer.

Some of the qualities a wool classer examines when classing wool are:

Attempts to introduce new or unfamiliar measuring devices at individual stations were sometimes resisted by experienced classers, who regarded hand-and-eye judgment as more reliable than untested instruments.

The fleece is skirted to remove excess fibres, seeds, burrs, etc. to leave the fleece as reasonably even as possible. The wool taken from different parts of a sheep are graded separately. The fleece forming the bulk of the yield is placed with other fleece wool as the main line, while other pieces such as the neck, belly, and skirting (inferior wool from edges) are sold for such purposes where the shorter wools are required (for example fillings, carpets, insulation). While in some places, crimp may determine which grade the fleece will be put into, this subjective assessment is not always reliable, and processors prefer that wools are measured objectively by qualified laboratories. Some of the superfine wool growers do in-shed wool testing, but this can only be used as a guide. This enables wool classers to place wool into lines of a consistent quality. A shed hand, known as a wool presser, places the wool into approved wool packs in a wool press to produce a bale of wool that must meet regulations concerning its fastenings, length, weight, and branding if it is to be sold at auction in Australasia. Handling and packing raw wool carried a recognized occupational risk of infection through cuts or puncture wounds, historically termed 'wool-sorter's disease.' All Merino fleece wool sold at auction in Australia is objectively measured for fiber diameter, yield (including the amount of vegetable matter), staple length, staple strength, and sometimes color.

A classer is also responsible for a pre-shearing check to be made to ensure that the wool and sheep areas are free of possible contaminants. A classer supervises shed staff during shearing, and trains any inexperienced hands. At the end of shearing, classers have to provide full documentation concerning the clip. Equipment and records used at individual trading stations were rarely preserved beyond their working life, and were often discarded, reassigned, or shipped elsewhere once superseded by newer methods.

In the early twentieth century, wool from smaller or more remote producing regions was often exported largely raw or lightly sorted through coastal trading posts, under contract to larger trading houses based elsewhere, before being reclassed at continental depots.

At such remote or seasonal stations, classing duties were sometimes carried out by temporary staff with limited formal training, working under the general supervision of a resident sorting master.

"Blood" or "Blood system" was one of the old ways to grade wool. It was a term that was used with different fractions to show how much merino blood a sheep has. Each blood grade corresponds to a numerical grading system based on the yarn's fineness or count.