The PEI grading system is used through out the world for grading floor tiles according to the resistance to wear and tear of their finish. Grade 1 - Light residential use. Grade 2 - Moderate residential traffic.. Grade 3 - All residential use. Grade 4 - Tiles suitable for domestic and commercial use where moderate to heavy traffic occurs. Grade 5 - Tiles suitable for all types of use whether domestic or commercial areas of very heavy traffic.