Measure your walls before you even think about picking a pattern. Get this wrong, and you’ll either run out of paper mid-project or have way too much left over, which costs money and creates waste. You need a sturdy tape measure, a pencil, and a calculator. Don’t rely on your phone’s calculator for anything complex; a dedicated one is better for accuracy.
calculating single wall dimensions
Start with a single wall. Measure its width at the top, middle, and bottom. Use the longest measurement. Record this number in inches. For example, if the top is 118 inches, the middle 119 inches, and the bottom 118.5 inches, write down 119 inches. This accounts for any slight imperfections in your wall or ceiling. Always measure at least three points and use the largest reading.
Next, measure the height of the wall. Measure from the ceiling to the baseboard. Again, measure in at least three different spots along the wall’s length and use the longest measurement. If your wall height varies, the extra paper is better than not enough. Record this height in inches.
Multiply the width (in inches) by the height (in inches) to get the square inches of the wall. For instance, 119 inches (width) x 96 inches (height) = 11,424 square inches.
accounting for doors and windows
Now, you need to subtract the areas of any doors and windows. Measure the width and height of each door and window opening in inches. Multiply the width by the height for each to get its square inches. A standard interior door might be 30 inches wide by 80 inches high (2,400 sq in). A window might be 48 inches wide by 60 inches high (2,880 sq in).
Subtract the square inches of each door and window from the total square inches of the wall. If a wall has a door and a window, you’d subtract both their areas from the wall’s total area. For our example wall (11,424 sq in), subtracting a door (2,400 sq in) and a window (2,880 sq in) leaves you with 6,144 sq inches of wallpaperable area on that specific wall.
how to measure for windows and doors correctly
When measuring windows and doors, extend your tape measure slightly beyond the opening on all sides. This extra inch or two per dimension is crucial. You’ll trim this excess when hanging the wallpaper, but it prevents you from ending up short if the pattern repeat is large or if you need to wrap the paper around a window frame slightly.
For windows, measure from the top of the trim to the bottom of the trim. For doors, measure from the top of the door frame to the bottom of the door frame. If there’s no trim, measure from the wall edge to the wall edge. Always add about 2 to 3 inches to both the width and height measurements to give yourself a buffer. This extra bit is essential for trimming and ensuring you have enough paper to work with, especially around intricate frames or moldings.
calculating for multiple walls and rooms
Repeat the process for every wall in the room that you plan to wallpaper. Add up the wallpaperable square inches for all the walls. For example, if you have four walls, each measuring 119 inches wide and 96 inches high, and each with one door and one window, your calculations would look like this:
Each wall’s wallpaperable area: (119″ W x 96″ H) – (30″ W x 80″ H) – (48″ W x 60″ H) = 11,424 sq in – 2,400 sq in – 2,880 sq in = 6,144 sq in.
Total wallpaperable area for four walls: 6,144 sq in/wall x 4 walls = 24,576 sq in.
It’s often easier to convert your measurements to feet and square feet early on. To do this, divide all your inch measurements by 12. So, a 119-inch width becomes 9.92 feet (approx. 10 ft), and a 96-inch height becomes 8 feet.
Wall Area (sq ft): 10 ft (W) x 8 ft (H) = 80 sq ft.
Door Area (sq ft): (30″ / 12) x (80″ / 12) = 2.5 ft x 6.67 ft = 16.67 sq ft.
Window Area (sq ft): (48″ / 12) x (60″ / 12) = 4 ft x 5 ft = 20 sq ft.
Wallpaperable Area per Wall (sq ft): 80 sq ft – 16.67 sq ft – 20 sq ft = 43.33 sq ft.
Total Wallpaperable Area (sq ft): 43.33 sq ft/wall x 4 walls = 173.32 sq ft.
how to measure for corners and angled walls
For inside corners, measure across the corner at the top, middle, and bottom, and use the longest measurement to determine the width of the paper needed for that section. You’ll typically want to extend the wallpaper about 1/2 inch around the corner onto the adjacent wall. This overlap allows for a clean seam and prevents any gaps.
For outside corners, measure from the corner edge onto the wall. Again, extend the paper about 1/2 inch around the corner onto the adjacent wall. Ensure the paper on the first wall is cut precisely at the corner, and the paper on the second wall starts just past the corner edge. Seams on outside corners are more visible, so precise cuts are key.
Angled walls or sloped ceilings require extra care. Measure the longest point of the slope from the ceiling to the baseboard. You’ll need to account for the angle when cutting your strips. It’s best to cut your wallpaper strips slightly longer than you think you’ll need to accommodate the angle and potential pattern matching.
understanding wallpaper rolls and coverage
Wallpaper is sold in rolls, and each roll covers a specific area. This is usually stated by the manufacturer. A standard US single roll is typically 20.5 inches wide and 27 feet long. This covers approximately 56 square feet.
However, the most critical factor is the pattern repeat. The pattern repeat is the vertical distance before the pattern begins to repeat. This can range from 0 inches (a random match) to over 24 inches. A large pattern repeat means you’ll waste more paper when matching the design from one strip to the next.
How to calculate pattern repeat waste:
Let’s say your wall height is 96 inches (8 feet) and your pattern repeat is 24 inches.
You will need to cut strips that accommodate this repeat. For an 8-foot wall, you might need to cut strips that are 8 feet plus one full pattern repeat (24 inches or 2 feet). So, you’d be cutting strips from your roll that are 10 feet long.
A standard US double roll (often sold as one continuous roll) is 20.5 inches wide and 54 feet long, covering about 112 square feet. Some manufacturers sell single rolls. Always check the product details.
how to convert measurements for the calculator
Most online wallpaper calculators ask for measurements in feet or square feet. If you’ve measured in inches, you need to convert. Divide your total wall width and height measurements (in inches) by 12 to get feet. For example, if your wall is 119 inches wide, that’s 119 / 12 = 9.92 feet.
If you’re using a calculator that asks for square feet, multiply your converted width in feet by your converted height in feet. So, for a wall that’s 9.92 ft wide and 8 ft high, the area is 9.92 ft x 8 ft = 79.36 sq ft.
Remember to account for doors and windows by subtracting their areas in square feet. If your calculator requires you to input total square footage of the room, calculate the total square footage of the walls, then subtract the square footage of doors and windows. For a more precise calculation, it’s better to input individual wall dimensions if the calculator allows it.
the importance of pattern repeat
The pattern repeat is arguably the most critical measurement after wall height and width. If you have a large pattern repeat, you will use significantly more wallpaper than a simple calculation of wall area might suggest. Manufacturers list the pattern repeat, often in inches, on the wallpaper’s packaging or product description.
Example:
Wall height: 8 feet (96 inches)
Pattern repeat: 20 inches
For each strip, you need to cut enough length to cover the wall height plus one full pattern repeat to ensure the pattern aligns perfectly with the next strip. So, you’ll need to cut strips that are 96 inches + 20 inches = 116 inches long.
If you are covering a standard 20.5-inch wide strip of wallpaper, and you are cutting 116-inch lengths, you need to see how many of these 116-inch lengths you can get from a standard roll (which is typically 27 feet or 324 inches long for a single roll).
Number of strips per single roll: 324 inches / 116 inches per strip = 2.79 strips. You can only get 2 full strips from a single roll.
This means for a wall requiring strips that are 116 inches long, you’ll get about 2.79 times the width of the wallpaper (20.5 inches) from a single roll. This is significantly less coverage than if there were no pattern repeat.
how to calculate rolls needed with pattern repeat
To calculate rolls needed: First, determine the number of strips you need to cover the total width of your walls. Divide the total width of your walls (in inches) by the width of the wallpaper (usually 20.5 inches). Round up to the nearest whole number.
Total wall width: Let’s say 4 walls, each 119 inches wide. Total width = 4 x 119 = 476 inches.
Number of strips needed: 476 inches / 20.5 inches per strip = 23.22 strips. You need 24 strips.
Next, determine the length of each strip, which is your wall height plus one pattern repeat (and add a few extra inches for trimming). Let’s use our example of 96-inch wall height and 20-inch repeat, so strip length = 116 inches.
Now, calculate how many usable strips you can get from one roll. A standard US single roll is 27 feet long, or 324 inches. Number of usable strips per roll = 324 inches / 116 inches per strip = 2.79. You get 2 usable strips per roll.
Finally, divide the total number of strips needed by the number of usable strips per roll: 24 strips needed / 2 strips per roll = 12 rolls.
If you didn’t account for the pattern repeat and assumed you could get more strips per roll (e.g., if your wall height was 8ft and you assumed you could get 3 strips per roll), you might only order 8 rolls (24 strips / 3 strips per roll), and you’d run out. Always factor in the pattern repeat.
using a wallpaper calculator effectively
A wallpaper calculator is a useful tool, but it’s only as good as the information you feed it. Here’s how to use one correctly:
1. Gather your measurements: Have your wall heights, widths, and door/window dimensions ready, all in inches.
2. Convert to feet (if necessary): Most calculators use feet. Divide all inch measurements by 12. For example, 96 inches becomes 8 feet.
3. Input wall dimensions: Enter the height and width for each wall. Some calculators allow you to input dimensions for individual walls, which is the most accurate method. Others ask for the total square footage of the room.
4. Account for openings: Subtract the square footage of doors and windows. Some calculators have specific fields for this.
5. Enter pattern repeat: This is crucial. Input the pattern repeat number in inches as specified by the wallpaper manufacturer. This is where many simple area calculations fail.
6. Specify roll size: Ensure the calculator knows if you’re using US single rolls (20.5″ x 27′) or double rolls (20.5″ x 54′).
A good calculator will use these inputs to determine the number of strips you can get from each roll, considering the pattern repeat, and then tell you how many rolls to buy. Always round up to the nearest whole roll.
common measuring mistakes to avoid
Mistake 1: Not measuring in multiple places. Walls aren’t perfectly straight. Measuring only at the top might miss a bulge or lean in the middle.
Mistake 2: Forgetting pattern repeat. This is the number one reason people run out of wallpaper. A large repeat means fewer usable strips per roll.
Mistake 3: Underestimating door and window allowances. You need extra material to trim around these openings cleanly.
Mistake 4: Ignoring ceiling height variations. If your ceiling isn’t perfectly flat or slopes, measure the longest point.
Mistake 5: Not adding buffer for trimming. Always add at least 2 inches to the height measurement for trimming at the ceiling and baseboard.
Mistake 6: Assuming all rolls are the same size. Check the manufacturer’s specifications. Some rolls are larger or smaller than the standard.
Mistake 7: Measuring in centimeters and converting incorrectly. If your wallpaper or room dimensions are in metric, convert carefully to imperial units (feet/inches) for most US-based calculators and rolls.
final check before ordering
Once you’ve used the calculator, do a final manual check. Take your total square footage of wallpaperable wall space and divide it by the square footage covered by one roll (factoring in pattern repeat waste if you can estimate it). Does the number of rolls the calculator suggests seem reasonable?
If you’re using patterned wallpaper, especially with a large repeat, it’s always better to buy one extra roll than to run short. Running out of wallpaper means you might not be able to find the same dye lot later, leading to color variations. This is especially true for antique wallpaper murals, where precise matching is critical.
Consider the type of wallpaper as well. Some materials, like grasscloth, are more delicate and might require slightly more material for careful handling. For most standard vinyl or paper wallpapers, following these measurement and calculation steps will get you the right amount. If you’re unsure, consult the wallpaper manufacturer’s guidelines or a professional installer. For a rough estimate of installation labor costs, you can use a wallpaper installation cost calculator.