Wallpapering a room is a rewarding DIY project, but accurate measurement is key to avoiding waste and ensuring you buy the right amount of material. This calculator helps you determine the total square footage of wallpaper needed for your project and estimates the number of rolls required based on standard roll sizes and pattern repeats.
How the Calculation Works:
The process involves calculating the total wall area and then subtracting the areas of any openings like doors and windows. We also consider the pattern repeat, which affects how much wallpaper you might use due to matching patterns.
1. Wall Area Calculation:
First, we calculate the perimeter of the room by adding up the lengths of all four walls. For a rectangular room, this is:
Perimeter = 2 * (Room Length + Room Width)
Then, we multiply the perimeter by the room's height to get the total gross wall area:
Gross Wall Area = Perimeter * Room Height
2. Area of Openings:
Next, we subtract the areas of doors and windows. These areas don't need wallpaper.
Door Area = Door Width * Door Height
For windows, we calculate the area of a single window and multiply it by the number of windows:
Window Area = (Window Width * Window Height) * Number of Windows
The net wall area is then:
Net Wall Area = Gross Wall Area – Door Area – Window Area
3. Accounting for Pattern Repeat:
Wallpaper often has a pattern that needs to be matched between strips. A pattern repeat is the distance before the pattern starts to repeat. A larger pattern repeat means more waste because you often have to cut away sections to align the pattern correctly. For simplicity in this calculator, we add a small percentage to the net wall area to account for this waste. A common rule of thumb is to add 10-20% for rooms with a pattern repeat, especially for more complex patterns or if you are less experienced.
In this calculator, a basic adjustment is made by considering the pattern repeat as a factor in how many drops you might get from a roll, but a more precise method involves calculating the total length of all vertical strips needed and then determining how many full drops fit on a roll given the pattern repeat and ceiling height.
A standard wallpaper roll is typically 20.5 inches wide and 33 feet long (or approximately 56 square feet). However, the usable area is reduced by the pattern repeat. The number of drops you can get from a roll is approximately (Roll Length in inches / (Ceiling Height in inches + Pattern Repeat in inches)).
For this calculator, we are focusing on the total square footage needed and then using a standard assumption of usable square footage per roll, with an adjustment for pattern repeat consideration.
4. Calculating Rolls Needed:
To estimate the number of rolls, we divide the total required square footage by the usable square footage per roll. Standard rolls are often around 56 sq ft, but due to pattern matching and waste, it's safer to assume a lower usable amount, often around 40-50 sq ft, especially with larger pattern repeats.
This calculator uses a conservative estimate for usable square footage per roll (e.g., 50 sq ft) and rounds up to the nearest whole roll.
When to Use This Calculator:
Planning to wallpaper a room (living room, bedroom, hallway, etc.).
Calculating wallpaper needs for accent walls.
Estimating material for commercial spaces.
Determining how much wallpaper to purchase to avoid multiple trips to the store.
Always purchase slightly more wallpaper than calculated to account for errors, future repairs, or if you plan to re-wallpaper a section. It's better to have a little left over than to run out!
function calculateWallpaperArea() {
var roomLength = parseFloat(document.getElementById("roomLength").value);
var roomWidth = parseFloat(document.getElementById("roomWidth").value);
var roomHeight = parseFloat(document.getElementById("roomHeight").value);
var doorWidth = parseFloat(document.getElementById("doorWidth").value) || 0;
var doorHeight = parseFloat(document.getElementById("doorHeight").value) || 0;
var windowCount = parseInt(document.getElementById("windowCount").value) || 0;
var windowWidth = parseFloat(document.getElementById("windowWidth").value) || 0;
var windowHeight = parseFloat(document.getElementById("windowHeight").value) || 0;
var patternRepeat = parseFloat(document.getElementById("patternRepeat").value) || 0;
var totalSquareFootage = 0;
var rollsNeeded = 0;
// Input validation
if (isNaN(roomLength) || isNaN(roomWidth) || isNaN(roomHeight) || roomLength <= 0 || roomWidth <= 0 || roomHeight 0 && doorHeight 0 && doorWidth 0 && windowHeight 0 && windowWidth <= 0) {
alert("Please enter a valid Window Width if Window Height is provided.");
return;
}
// Calculate wall area
var perimeter = 2 * (roomLength + roomWidth);
var grossWallArea = perimeter * roomHeight;
// Calculate area of openings
var doorArea = doorWidth * doorHeight;
var totalWindowArea = windowCount * (windowWidth * windowHeight);
// Calculate net wall area
var netWallArea = grossWallArea – doorArea – totalWindowArea;
// Ensure net area is not negative
if (netWallArea < 0) {
netWallArea = 0;
}
// Add allowance for pattern repeat and waste
// A common rule of thumb is to add 10-20% for pattern matching and waste.
// We'll add 15% as a general allowance.
var wasteAllowance = 0.15; // 15%
totalSquareFootage = netWallArea * (1 + wasteAllowance);
// Calculate rolls needed
// Standard wallpaper roll: ~20.5 inches wide, 33 feet long = ~56 sq ft.
// However, usable area is less due to pattern matching.
// Let's assume a usable area of around 45 sq ft per roll for calculation,
// which accounts for pattern repeat and trim waste.
var usableSqFtPerRoll = 45; // This is a conservative estimate
// If pattern repeat is provided, and it's a significant value relative to height,
// we might need more rolls. A more advanced calculation would determine
// drops per roll based on height and repeat. For simplicity here, we use a fixed usable sqft.
// If patternRepeat is very large, this estimation might need refinement.
// For this simplified model, we assume 'usableSqFtPerRoll' already factors in typical waste.
rollsNeeded = Math.ceil(totalSquareFootage / usableSqFtPerRoll);
// Display results
document.getElementById("totalSquareFootage").textContent = totalSquareFootage.toFixed(2);
document.getElementById("rollsNeeded").textContent = rollsNeeded;
}