A tile spec sheet prints four durability numbers, and each one points to a specific place the tile belongs: the PEI wear class (from the Porcelain Enamel Institute), the water-absorption group, the Mohs surface hardness, and the breaking strength. Learn to read those four and a wall of symbols turns into one plain question about any tile. Is it right for this room? A backsplash and a mudroom floor need almost opposite tiles, and the ratings are how you tell them apart. Here's what each number measures and the room it sends you to.
What Does the PEI Rating Mean on a Tile?
The PEI rating is a tile's abrasion class, a 0-to-5 score for how well a glazed surface stands up to foot traffic and grit. The number comes from the ISO 10545-7 surface-abrasion test, where a loaded abrasive is spun on the glaze until wear shows; more revolutions before wear means a higher class. A low number is light duty, a high number is heavy traffic. The class isn't a quality grade. It's a direct map to where the tile can go, and the international tile specification called ISO 13006 spells out the rooms for each class in an annex most shoppers never see. The table below is that map in plain terms, so a rating on a sample board becomes a room in your house.
PEI class | What it handles | Where it belongs |
|---|---|---|
Class 0 | No foot traffic | Walls only |
Class 1 | Bare or soft-soled feet, no grit | Bath or bedroom with no outside door |
Class 2 | Light traffic, little grit | Living areas, not kitchens or entries |
Class 3 | Normal traffic, some grit | Residential kitchens, halls, terraces |
Class 4 | Regular traffic, more grit | Entries, hotels, light commercial |
Class 5 | Severe, sustained traffic | Malls, airports, industrial floors |
For a house, PEI Class 3 is the honest floor for most rooms, and Class 4 buys margin where a family tracks in sand and snow. Anything rated Class 0 or 1 is a wall tile, full stop, and putting it on a floor is the most common rating mistake we see. A backsplash can be Class 0 and it will look new for decades. A busy mudroom wants Class 4. Match the class to the traffic and the tile lasts as long as the grout does.
What Does the Water-Absorption Rating Tell You?
The water-absorption rating tells you how porous the tile body is, measured as the percentage of its weight in water it soaks up during the ASTM C373 or ISO 10545-3 soak test. Less absorption means a denser, tougher, more water-tolerant tile. The line worth memorizing is 0.5%: at 0.5% or less the tile is impervious, the class the industry calls porcelain. Above that, ISO 13006 sorts tile into rising bands, up to 3%, up to 6%, up to 10%, and over 10% for the thirstiest wall tile. US spec sheets often use older words for the same idea, impervious, vitreous, semi-vitreous, and non-vitreous, as the porosity climbs. The exact cut points differ a little between the ANSI and ISO versions, so treat the names as a guide and the number as the fact: the lower the percentage, the less water the tile drinks, and the wetter or colder the spot it can handle.
Water absorption | ISO group and name | Best use |
|---|---|---|
0.5% or less | BIa, impervious (porcelain) | Wet areas, outdoors, any floor |
Over 0.5% to 3% | BIb, vitreous | Most indoor floors and walls |
Over 3% to 6% | BIIa, semi-vitreous | Indoor walls, light-traffic floors |
Over 6% to 10% | BIIb | Indoor walls |
Over 10% | BIII, non-vitreous | Dry walls only |
Absorption is also the outdoor test. Water that soaks into a porous tile and then freezes will expand and break the tile or its bond, which is why the ASTM C1026 freeze-thaw test exists and why only impervious, low-absorption tile belongs on a Westchester porch or an unheated Yonkers entry. Indoors, a 3% vitreous tile is fine on a bedroom floor and a poor idea in a shower. The number tells you the room.
What Does Mohs Hardness Measure on a Tile?
Mohs hardness measures how well a tile's surface resists scratching, on a 1-to-10 mineral scale that runs from talc at 1 up to diamond at 10 for the hardest mineral. The number that matters for a floor is 7. Quartz sits at 7, and quartz is the main mineral in the sand and grit that rides in on shoes, so any surface softer than 7 will scratch and haze over time. For reference, a fingernail is about 2 to 2.5 and a steel knife blade about 5 to 6.5, both softer than the grit already on your floor. A glazed tile carries the hardness of its glaze, which varies by product. Through-body porcelain, colored all the way through, wears more evenly because there's no thin glaze layer to grind off, and that's part of why it holds up in high-grit rooms. When a showroom tile lists a Mohs number, 7 or above is what you want underfoot.
What Is Breaking Strength, and Why Is It on the Box?
Breaking strength is a tile's resistance to cracking under load, and for floor tile it's close to pass-or-fail. Measured by ISO 10545-4, or ASTM C648 in North America, it's reported as the force a tile takes before it snaps. ANSI A137.1 sets the bar for pressed floor tile at a 250-pound minimum average, so any tile going on a floor should meet or beat it. Wall tile can be weaker, since nothing stands on it. Here's the catch worth knowing: even a strong tile cracks over a bad subfloor. A tile bridges a hollow or a flexing seam and then breaks along the gap, which is why the number on the box is only half the story and the surface under the tile is the other half. Our guide to subfloor prep in older Westchester homes covers the flatness and moisture checks that let a tile's breaking strength actually do its job.
Reading All Four Ratings Together
Reading all four ratings together is how you turn a spec sheet into a decision, because a floor tile has to pass every one of them, and the rating you skipped is usually the one that fails. A good bathroom-floor tile is impervious or close to it, rated at least PEI Class 2, hard enough near 7 on the Mohs scale to resist grit, and over the 250-pound breaking-strength floor. Miss one and the floor disappoints in its own way: a low PEI dulls, a high absorption fails in the wet, a soft glaze scratches, a weak body cracks. There's a fifth number for wet rooms, the DCOF slip rating, where the tile industry sets 0.42 as the wet-floor minimum for level interior tile walked on when wet. It measures grip rather than durability, but it earns a spot on the same checklist. You can find the full rating data on the boxes and cut sheets for the tile we carry in the showrooms.
Questions We Hear About Tile Ratings
What PEI rating do I need for a kitchen floor?
A kitchen floor needs at least PEI Class 3, the class ISO 13006 maps to residential kitchens, halls, and other rooms that see regular grit. Class 4 is the safer pick in a busy family kitchen or one with a door straight to the yard. Below Class 3, a kitchen floor starts showing wear paths within a few years.
Is a higher PEI rating always better?
A higher PEI rating isn't automatically better; it helps only if you need the wear resistance. Very hard, high-class glazes can be more slippery and come in fewer looks, so a Class 5 industrial tile is overkill and sometimes a step down in a quiet powder room. Buy the class the room's traffic calls for and stop there.
Does water absorption decide if a tile can go outside?
Water absorption is the rating that decides outdoor use, because a porous tile that soaks up water will crack when that water freezes. For a Westchester patio or step, choose an impervious tile at 0.5% absorption or less and confirm it's rated for freeze-thaw, the property the ASTM C1026 test checks. A pretty indoor tile set outdoors is a one-winter mistake.
What Mohs hardness should a floor tile be?
A floor tile should sit at 7 or higher on the Mohs scale to resist the quartz grit tracked in on shoes, which is itself a 7. Wall tile can be softer, since nothing scratches it. If a spec sheet doesn't list a Mohs number, a through-body porcelain is the safe default for a high-traffic floor.
Turning Tile Ratings Into the Right Floor
The four ratings work as a set: PEI for traffic, water absorption for wet and cold, Mohs for grit, and breaking strength for load. Read together, they tell you which tile belongs in a kitchen, a shower, a mudroom, or a patio, and they take the guesswork out of a showroom full of options that all look the same on the wall. If you'd rather not decode a stack of cut sheets alone, bring your rooms to us. Our design team reads these specs every day, and when you're ready to measure and price it, request a free in-home estimate and our installers will match the ratings to the rooms they're going in.
