Reading a wallcovering sample book: repeat, match, and railroading

The pretty side of a sample book is the pattern. The useful side is the small block of specifications printed beside it, because those numbers decide how much material a job needs and how it has to be hung. Here is what the five entries that actually matter mean, and why each one changes the order.

Roll units. American wallpaper is quoted in a way that trips up newcomers: it is priced by the single roll, which historically covers roughly 36 square feet, but almost always packaged and sold in double-roll bolts of about 72 square feet, and imported goods often come in longer metric rolls. Commercial vinyl, by contrast, is usually 54 inches wide and sold by the linear yard. Confirming the unit before you multiply is the first defense against ordering half or twice what the wall needs.

Pattern repeat. This is the vertical distance before the design starts over. A large repeat is dramatic and wasteful at the same time: the installer aligns each strip to the one beside it, and the taller the repeat, the more material gets trimmed away to make that alignment work. It is the main reason the same square footage of wall can need very different amounts of two different patterns.

Match. This tells the installer how adjacent strips line up. A straight match, or straight-across, keeps the pattern level at the same height on every strip. A drop match, commonly a half-drop, shifts every other strip down by half the repeat, so the design steps diagonally across the wall and eats more material for the same wall. That extra belongs in the order, not in a hopeful estimate.

Railroading. A railroaded material is printed so the pattern runs along the roll's length rather than up its width, which lets an installer run a long horizontal band, such as a wainscot or a low banquette wall, without a vertical seam. Not every pattern can be railroaded, and the sample book will say so.

Dye lot, sometimes called the run number, is the specific production batch. Color drifts slightly between lots, so all material for one continuous space should come from a single lot, which is why the trade orders the whole job at once with overage built in rather than topping up later. As a rough guide that is 10 percent on a straight match and 15 to 20 percent on a large drop, more when the repeat is tall, but the installer should really calculate it strip by strip against the actual repeat rather than trust a flat number. Miss any one of these five and the wall tells on you.