The most common mistake people make when wallpapering is buying too little or too much. Getting it right saves money and prevents the headache of running out mid-project or having stacks of unused rolls.
Measure your walls accurately
Before you even think about patterns or colors, you need precise measurements. You’ll need a tape measure, a pencil, and a calculator.
How to measure for wallpaper
- Measure the width of each wall. Measure from corner to corner. If you have multiple walls in a single room, measure each one individually. Don’t assume all walls are the same length.
- Measure the height of each wall. Measure from the ceiling line to the baseboard. Again, measure each wall separately.
- Subtract windows and doors. For each window and door, measure its width and height. Calculate the square footage of each opening (width x height). Subtract these areas from the total square footage of the walls.
Example: If a wall is 10 feet wide and 8 feet high, its area is 80 sq ft. If it has a window that is 3 feet wide and 4 feet high (12 sq ft), the usable wall area for wallpaper is 80 – 12 = 68 sq ft.
Understand wallpaper roll dimensions
Wallpaper comes in rolls of varying sizes. The most common sizes in the US are:
- Standard double roll: Approximately 20.5 inches wide by 33 feet long. This covers about 56.4 sq ft.
- Metric single roll: Often around 20.5 inches wide by 19.7 feet long, covering about 33 sq ft. Many US manufacturers still sell in double rolls, but it’s crucial to check the packaging.
Always check the specific roll size on the packaging. Don’t assume it’s a standard size. If you’re looking at Lewis and Wood wallpaper or other premium brands, confirm their dimensions.
Calculate wallpaper needed based on pattern repeat
This is where things get tricky for many DIYers. The pattern repeat (also called the ‘drop’) is the vertical distance on the wallpaper where the pattern matches from one strip to the next. A large pattern repeat means you’ll waste more wallpaper as you cut strips to align the design.
Types of pattern repeat:
- Straight match: The pattern matches from one strip to the next without any offset. This is the most common and easiest to work with.
- Half-drop match: The pattern on one strip matches with the pattern halfway down the adjacent strip. This requires more careful cutting and leads to more waste.
- Random match: The pattern doesn’t need to align between strips. This is rare but is the most forgiving for installation and waste.
How pattern repeat affects your calculation:
A large pattern repeat means you need to ‘buy into’ the pattern. If your wall height is 8 feet and your pattern repeat is 24 inches (2 feet), you’ll get fewer full strips from a roll because you have to cut off the excess to get to the next repeat. If a roll is 33 feet long and your wall height is 8 feet, you might expect to get 4 strips (33 / 8 = 4.125). However, if the pattern repeat is 24 inches, and you need to align it perfectly, you might only get 3 usable strips from that 33-foot roll if your ceiling height isn’t a clean multiple of the repeat.
The practical way to calculate with pattern repeat:
- Determine your wall height.
- Find the pattern repeat on the wallpaper specifications.
- Calculate how many strips you can get from one roll. Divide the roll length by your wall height. Then, adjust this number downwards if the pattern repeat forces you to cut off significant portions. A good rule of thumb is to assume you’ll get 3-4 full strips from a standard double roll if the pattern repeat is large or your ceiling height is awkward. For smaller repeats and standard ceiling heights (8ft), you might get 4-5 strips.
- Calculate the total number of strips needed. Divide the total width of your walls (including any pattern matching adjustments needed at corners) by the width of the wallpaper roll.
- Divide total strips needed by strips per roll. This gives you the number of rolls. Always round up to the next whole number.
Using a wallpaper calculator
Manually calculating can be tedious and prone to error. Using an online wallpaper calculator is highly recommended. You input your room dimensions, and the calculator accounts for standard roll sizes and often allows you to input the pattern repeat.
For instance, our how much wallpaper do i need calculator can help streamline this process. These tools are designed to take the guesswork out of ordering.
Factors that increase waste (and require more rolls)
- Large pattern repeats: As mentioned, these force you to cut away more material to match the design.
- Half-drop matches: You’ll get fewer usable strips per roll.
- Obstacles: Alcoves, bay windows, fireplaces, and uneven walls will require more cuts and more careful pattern matching, leading to increased waste.
- Doors and windows: While you subtract their area, you still need to cut around them, which can disrupt the pattern flow and require extra pieces.
- First-time installers: It’s wise to buy an extra roll if you’re new to wallpapering. Mistakes happen, and having a backup prevents a project stoppage.
The crucial ‘extra roll’ rule
It’s almost always recommended to buy at least one extra roll of wallpaper. Why?
- Future repairs: Years down the line, you might need to patch a small damaged area. If you don’t have extra, you might not be able to find the exact same dye lot or batch number, making a perfect match impossible.
- Installation errors: You might cut a strip too short, make a mistake aligning the pattern, or damage a piece during application.
- Dye lot variations: Wallpaper is printed in batches called ‘dye lots.’ Even rolls of the same pattern can have slight color variations between different dye lots. Buying all your wallpaper from the same lot ensures color consistency. An extra roll ensures you have matching color and pattern for repairs.
If you’re wallpapering a very large room or have a complex design, consider buying two extra rolls.
Common pitfalls to avoid
- Assuming all rolls are the same size: Always check the dimensions on the packaging.
- Ignoring the pattern repeat: This is the biggest cause of running short.
- Not accounting for waste: Especially with busy patterns or complex room layouts.
- Buying from different dye lots: This leads to color mismatching.
- Not buying an extra roll: For repairs or mistakes.
- Using the wrong glue: Ensure you have appropriate clear wallpaper glue if needed, especially for older types of wallpaper or specific hanging methods.
Wallpapering over existing surfaces
If you’re applying wallpaper over a surface like wood paneling, you need to consider the surface’s texture and if primer is needed. For peel and stick wallpaper over wood paneling, the installation is different, but calculating the quantity still follows the same principles of wall area and pattern repeat. Ensure the surface is smooth and clean for any wallpaper type.
Consider antique wallpaper rolls
If you’re opting for antique wallpaper rolls, be aware that their dimensions and quality can vary significantly. These often come in smaller rolls and may have different pattern repeat sizes. Always verify the exact dimensions and condition of antique rolls before purchasing and calculate carefully.
Final check on your calculation
Once you’ve done your calculations, double-check everything. Measure twice, cut once, and order once. The total square footage of your walls minus openings, divided by the square footage coverage per roll, is your starting point. Then, adjust for pattern repeat and add an extra roll for safety and future needs.
