Wallpaper Calculator

The core of the calculation is determining how many vertical strips (or “drops”) of wallpaper you need to cover your walls and how many of those drops you can get out of a single roll. We start by calculating the total perimeter of the room (e.g., (Length + Width) x 2) and dividing it by the width of your wallpaper roll. This tells you the total number of drops required to cover all the walls from corner to corner. We calculate the area of solid walls, ignoring minor openings like standard doors and windows, as the paper cut from these areas is often used for trimming above and below them.

The next step is figuring out how many drops you can realistically cut from one roll. This isn’t as simple as dividing the roll’s length by your wall height. You must also account for the “pattern repeat”—the vertical distance before the wallpaper’s design repeats itself. To ensure the pattern matches seamlessly between adjacent drops, each cut must start at the same point in the pattern. This means the length of each drop you cut must be a multiple of the pattern repeat that is greater than your wall height. This often generates significant, but necessary, waste. The final roll count comes from dividing the total drops needed by the number of usable drops per roll, always rounding up.

Let's calculate the wallpaper needed for a standard bedroom that is 12 feet long and 10 feet wide with an 8-foot ceiling. The wallpaper chosen is a standard American roll, which is 20.5 inches wide and 33 feet long, and features an 18-inch pattern repeat.

First, find the wall perimeter: (12 ft + 10 ft) x 2 = 44 feet. Now, find the number of drops needed: 44 ft / (20.5 inches / 12) = 25.75 drops. We must round up, so we need 26 drops total.

Next, determine the cut length for each drop, accounting for the pattern. The wall height is 8 feet (96 inches). We must cut a length that is a multiple of the 18-inch repeat and taller than 96 inches. The smallest multiple of 18 that exceeds 96 is 108 inches (18 x 6), which is 9 feet. So, each drop we cut will be 9 feet long.

A common question is whether to subtract the area of windows and doors. For most projects, the answer is no. Do not subtract these areas from your total wall measurements. The paper that would have covered these openings is not entirely waste; it is often essential for the smaller pieces needed to fit above headers, below sills, and around casings. Calculating the full wall area provides a built-in buffer that ensures you have enough paper for these tricky cuts. Attempting to subtract these areas often leads to shortages, especially with large pattern repeats.

On top of this, our calculator adds a standard 15% waste factor. This isn't just for show—it is a crucial buffer that professionals rely on. This additional quantity accounts for cutting errors, misaligned patterns, and complex areas that may require a fresh piece. It also gives you a small reserve for potential future repairs. For intricate layouts, rooms with many obstacles (outlets, switches, sconces), or for beginners who may make more mistakes, increasing this waste percentage can provide valuable peace of mind and prevent a last-minute scramble for more paper.

Always purchase all the rolls you need in a single transaction and verify they are from the same batch or dye lot. You can find the batch number printed on the wallpaper’s label. Different batches can have slight color variations that are unnoticeable in the store but become obvious once installed on the wall. Running short and buying a roll from a different batch later can ruin the look of an entire wall. To be safe, many people order one extra “attic roll” beyond the calculated amount. This roll, from the same dye lot, is a lifesaver for making invisible repairs years down the line.

Proper wall preparation ensures you don’t waste expensive wallpaper. Walls should be cleaned, smoothed, and primed with a wallpaper-specific primer. Applying paper to an unprepared, porous, or uneven surface can lead to poor adhesion, bubbling, and tearing, forcing you to waste material. Also, pay close attention to the manufacturer's instructions regarding “booking,” which is the process of letting the paste activate on the paper before hanging. Skipping this step can cause the paper to expand or shrink on the wall, creating gaps or bubbles and ruining your careful pattern alignment.