Rectified, Calibrated, and Natural Tile: ANSI A137.1
According to the ANSI A137.1 standard, the American National Standard Specifications for Ceramic Tile, rectified tile is tile that has had all edges mechanically finished to achieve a more precise facial dimension. Tile that skips that step is commonly called non-rectified, though that isn’t one of the standard’s category names. A137.1 instead classifies it as one of two categories: calibrated tile, which is sorted to meet a manufacturer’s stated caliber range, and natural tile, which is packaged directly after manufacturing without rectification or sorting.
For each category, A137.1 sets tolerance ranges for nominal size and wedging, a measure of how square a tile is. These ranges differ by tile type, which is why a rectified, calibrated, or natural label tells you how consistent a tile is likely to be in size and squareness.
What ANSI A137.1 Covers
ANSI A137.1 is the American National Standard for ceramic tile. It is developed by ANSI Accredited Standards Committee A108, with the Tile Council of North America (TCNA) serving as secretariat and publisher, and the current edition is A137.1-2022.
The standard covers the normally available sizes and shapes of ceramic tile, along with definitions, testing, marking, and certification. It also sets physical property requirements for Standard Grade, Second Grade, decorative, and specialty tile. It applies to several tile types, including mosaic, quarry, pressed floor, glazed wall, and porcelain tile, and the requirements vary by type. Glass tile and gauged porcelain tile and panels/slabs fall under separate standards, A137.2 and A137.3, so the tolerances in this article don’t apply to porcelain slabs.
Beyond dimensions, A137.1 addresses water absorption, breaking strength, and surface flatness, and it classifies color and texture variation into aesthetic classes from V0 to V4. Its dimensional requirements rely on standardized test methods for facial dimensions, wedging, and warpage, so a tile tested in one lab can be compared with a tile tested in another.
One point is easy to miss: A137.1 is a voluntary standard. Manufacturers aren’t required to make every product meet it, so compliance is something to confirm on a product’s technical data sheet rather than assume.
How ANSI A137.1 Defines Rectified Tile
Rectified tile starts out like any other ceramic or porcelain tile: it is shaped and fired in a kiln, whether glazed or unglazed. After firing, all of its edges are mechanically finished, typically by grinding or cutting, to bring the tile to a more precise facial dimension.
Rectified does not mean every tile is identical. A137.1 still sets tolerance ranges for nominal size and wedging within the rectified category. For rectified pressed floor tile and rectified porcelain tile 6 inches and larger:
- Nominal size: may fall between 3% under and 2% over the stated size.
- Wedging: limited to plus or minus 0.25%, capped at 0.03 inch.
The inch figure works as a ceiling, so allowable deviation doesn’t keep growing as tiles get larger. On a 24-inch rectified tile, for example, 0.25% would be 0.06 inch, but the cap holds the allowable wedging to 0.03 inch.
Rectification addresses length, width, and squareness. It does not remove warpage, the slight bowing that can occur in the tile body during firing. A137.1 sets warpage requirements separately, so a rectified tile can still carry some warp within its allowable range.
How ANSI A137.1 Defines Calibrated and Natural Tile
Tile that skips the post-firing edge-finishing step retains more of its as-fired size variation. It’s often called non-rectified, but A137.1 doesn’t use that as a category. Instead, it classifies this tile as either calibrated or natural, depending on what happens after firing.
Calibrated Tile
Calibrated tile isn’t mechanically finished. Instead, it is sorted after production to meet a manufacturer’s stated caliber range, which is why boxes of calibrated tile list a caliber or size code. For calibrated pressed floor tile and calibrated porcelain tile 6 inches and larger:
- Nominal size: may fall within 3% under or over the stated size.
- Wedging: limited to plus or minus 0.50%, capped at 0.08 inch.
Calibrated tile allows twice the wedging percentage of rectified tile. On a 24-inch tile, 0.50% would be 0.12 inch, so the cap holds the allowable wedging to 0.08 inch, compared with 0.03 inch for rectified.
Natural Tile
Natural tile is packaged directly after manufacturing and isn’t sorted by size, so it carries the widest tolerances of the three categories. For natural pressed floor tile:
- Nominal size: may fall within 4% under or over the stated size.
- Wedging: limited to plus or minus 1.00%, capped at 0.12 inch.
Not Every Category Applies to Every Tile Type
A137.1 doesn’t apply all three categories across the board. Pressed floor tile can be classified as natural, calibrated, or rectified, but porcelain tile is specified only as calibrated or rectified. Quarry, mosaic, and glazed wall tile have their own separate dimensional specifications.
Many calibrated and natural tiles also have a slightly rounded, cushioned edge, sometimes called a pillow edge. That profile is common, but it isn’t part of the A137.1 classification. Some cushioned edges are a design choice, so the edge alone doesn’t tell you which category a tile belongs to.
Reading ANSI A137.1 on a Spec Sheet or Box
Because A137.1 compliance is voluntary, the product’s documentation is where you confirm it. A technical data sheet that references A137.1 will typically list the tile’s dimensional category and its test results for wedging, warpage, and water absorption against the standard’s requirements. The box label often states whether a tile is rectified or not rectified, along with its caliber and shade.
Porcelain is a useful example of how A137.1 classifications show up on packaging. The standard defines porcelain as ceramic tile with water absorption of 0.5% or less, and only tile tested at or below that threshold can be certified as porcelain and carry the certification mark on its packaging. If a tile is marketed as porcelain but the data sheet doesn’t support it, that’s worth asking about before you buy.
If tile appears to fall outside its stated tolerances, independent lab testing against A137.1 can measure its actual size, wedging, and warpage. Those results give everyone involved a common reference point.
“Calibrated” in Natural Stone
The word “calibrated” also appears in natural stone fabrication, but it means something different there. In stone, calibration typically refers to grinding tile to a consistent thickness, not sorting ceramic tile by facial dimension.
ANSI A137.1 applies only to ceramic tile. Natural stone is covered instead by its own ASTM material specifications for dimension stone, with separate specifications for granite, marble, limestone, travertine, and other stone types. When a spec sheet says “calibrated,” confirm whether it describes ceramic tile or stone.
Choosing Between Rectified, Calibrated, and Natural Tile
None of the three categories is objectively better. Rectified tile’s tighter tolerances suit designs built around clean lines and minimal visible grout. Calibrated and natural tile can complement softer edges, more traditional styling, or layouts where the grout pattern is part of the look.
Cost is another consideration. The added edge-finishing step generally increases manufacturing cost, so rectified tile often costs more per square foot. Pricing still varies by manufacturer, material, size, and finish, so it’s worth comparing specific products rather than assuming.
The A137.1 aesthetic class matters here too. A tile’s V-rating describes how much color and texture variation to expect from piece to piece, which affects the finished look as much as its dimensional category.
Compare Rectified and Non-Rectified Tile With Our Design Team
If you’re weighing rectified and non-rectified options, our design team can help you read the spec sheets, confirm whether a product lists ANSI A137.1 compliance and its dimensional category, and see the difference side by side in our showrooms. Book a free design consultation and bring your project details, including the room, the layout you have in mind, and the look you want to achieve.
Frequently Asked Questions
Rectified tile has had all edges mechanically finished after firing for a more precise facial dimension. Calibrated tile is sorted after production to fall within a manufacturer’s stated size range. Natural tile is packaged directly after manufacturing without sorting. Calibrated and natural tile are often grouped together as non-rectified, but that term isn’t one of the standard’s categories. Each category has its own tolerance ranges for nominal size and wedging.
No. Calibrated tile is sorted after production to fall within a manufacturer’s stated caliber range, but it isn’t mechanically finished. Under A137.1, calibrated tile also allows more wedging than rectified tile. In natural stone, “calibrated” usually refers to grinding stone to a consistent thickness, which is a separate process.
No. A137.1 is a voluntary standard, and manufacturers aren’t required to make every product meet it. Check the product’s technical data sheet to confirm compliance and the tile’s dimensional category.
No. A137.1 specifies porcelain tile only as calibrated or rectified. The natural category applies to pressed floor tile.
Wedging measures how square a tile is. A137.1 limits it by category: for rectified pressed floor and porcelain tile 6 inches and larger, wedging is limited to plus or minus 0.25%, capped at 0.03 inch, while calibrated tile in the same size range allows plus or minus 0.50%, capped at 0.08 inch.
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