The number of stitches (tufts) per running inch of carpet usually is specified directly for tufted carpet, but is called rows per inch for woven carpet. The numerical product of tuft rows per inch of width multiplied by stitches per running inch is the number of tufts per square inch, or tuft density.

The classification system roughly defines what type of room each floor can be used in. Class 32, for instance, signifies that the floors in this class can be used for moderate commercial use, while class 33 signifies heavy commercial use.

Fire Ratings The ASTM system classifies a carpet as Class 1 or Class 2, while the EN system is more stringent and detailed. With the EN system, letters A through F indicate how combustible the material is, with A being non-combustible to F being easily flammable.