Wallpapering a room can transform its appearance, but accurately estimating the amount of wallpaper needed is crucial to avoid waste and multiple trips to the store. This calculator helps you determine the total yards of wallpaper required for your project, taking into account room dimensions, wallpaper specifications, and common architectural features.
The Math Behind the Calculation
The calculation involves several steps to ensure accuracy:
Calculate Total Wall Area: We first find the perimeter of the room by adding the lengths of all four walls (2 * Room Width + 2 * Room Length). This perimeter is then multiplied by the Room Height to get the gross square footage of the walls.
Calculate Area of Obstructions: The areas of doors and windows are subtracted from the total wall area.
Door Area = (Door Width / 12) * (Door Height / 12) * Door Quantity (if applicable, usually 1)
Calculate Net Wall Area: Subtract the total obstruction area from the gross wall area to get the net square footage of the walls that will be covered by wallpaper.
Determine Vertical Strips Needed: The room's perimeter (in feet) is divided by the wallpaper roll's width (converted from inches to feet) to determine how many vertical strips are needed.
Wallpaper Roll Width in Feet = Wallpaper Roll Width (inches) / 12
Number of Strips = (2 * Room Width + 2 * Room Length) / (Wallpaper Roll Width (inches) / 12)
Calculate Strip Length: Each strip's length is generally the Room Height. However, if there's a pattern repeat, you add the pattern repeat length to the Room Height to ensure the pattern aligns on subsequent strips.
Calculate Total Square Feet of Wallpaper: Multiply the number of strips by the length of each strip (including pattern repeat allowance).
Total Wallpaper Square Feet = Number of Strips * Strip Length (in feet)
Convert to Square Yards: Since wallpaper is often sold by the roll and coverage is discussed in square yards, we convert the total square feet to square yards by dividing by 9.
Total Square Yards = Total Wallpaper Square Feet / 9
Calculate Rolls Needed: The total square yards needed are divided by the square yards per roll. Note: standard wallpaper coverage is often cited in square yards per roll, but a roll's length is given in yards and width in inches. We've directly calculated total square yards required, so we need to compare this to the output of our calculation. A common rule of thumb is 1 roll covers approx 56 sq ft. The calculator aims to give total yards required for purchase, assuming a standard roll length of 11 yards. To find the number of rolls, we divide the total square yards by the square yards per roll.
Square Yards per Roll = (Wallpaper Roll Length (yards) * 3 feet/yard * Wallpaper Roll Width (inches) / 12 inches/foot) / 9 sq ft/sq yd
Number of Rolls = Total Square Yards Needed / Square Yards per Roll
Factor in Waste: It's standard practice to add 10-20% to the total calculated yardage for cuts, matching patterns, and potential mistakes. This calculator provides the base requirement, so consider ordering slightly more than the calculated amount.
When to Use This Calculator:
This calculator is ideal for anyone undertaking a wallpapering project, whether it's a single accent wall, a whole room, or even a hallway. It's particularly useful when:
Working with rooms that have standard rectangular dimensions.
Dealing with wallpaper that has a significant pattern repeat, which requires more paper to align.
Accounting for common features like doors and windows that reduce the actual wall space to be papered.
By inputting your specific measurements, you can get a reliable estimate, helping you purchase the right amount of wallpaper and ensure a smooth, professional finish.
function calculateWallpaper() {
var roomWidth = parseFloat(document.getElementById("roomWidth").value);
var roomLength = parseFloat(document.getElementById("roomLength").value);
var roomHeight = parseFloat(document.getElementById("roomHeight").value);
var wallpaperWidth = parseFloat(document.getElementById("wallpaperWidth").value);
var wallpaperLength = parseFloat(document.getElementById("wallpaperLength").value); // This is often a standard length for a roll (e.g., 11 yards)
var patternRepeat = parseFloat(document.getElementById("patternRepeat").value);
var doorWidth = parseFloat(document.getElementById("doorWidth").value);
var doorHeight = parseFloat(document.getElementById("doorHeight").value);
var windowWidth = parseFloat(document.getElementById("windowWidth").value);
var windowHeight = parseFloat(document.getElementById("windowHeight").value);
var windowQuantity = parseInt(document.getElementById("windowQuantity").value) || 0; // Default to 0 if not entered or invalid
var resultDisplay = document.getElementById("result-value");
// Input validation
if (isNaN(roomWidth) || isNaN(roomLength) || isNaN(roomHeight) ||
isNaN(wallpaperWidth) || isNaN(wallpaperLength) ||
isNaN(patternRepeat) || isNaN(doorWidth) || isNaN(doorHeight) ||
isNaN(windowWidth) || isNaN(windowHeight) || isNaN(windowQuantity)) {
resultDisplay.textContent = "Please enter valid numbers for all fields.";
resultDisplay.style.color = "#dc3545"; // Red for error
return;
}
if (roomWidth <= 0 || roomLength <= 0 || roomHeight <= 0 || wallpaperWidth <= 0 || wallpaperLength <= 0) {
resultDisplay.textContent = "Room and wallpaper dimensions must be positive.";
resultDisplay.style.color = "#dc3545";
return;
}
// Convert units to feet for calculations
var wallpaperWidthFt = wallpaperWidth / 12;
var patternRepeatFt = patternRepeat / 12;
var doorWidthFt = doorWidth / 12;
var doorHeightFt = doorHeight / 12;
var windowWidthFt = windowWidth / 12;
var windowHeightFt = windowHeight / 12;
// Calculate gross wall area
var roomPerimeter = (2 * roomWidth) + (2 * roomLength);
var grossWallAreaSqFt = roomPerimeter * roomHeight;
// Calculate area of obstructions
var doorAreaSqFt = (doorWidthFt * doorHeightFt);
var windowAreaSqFt = (windowWidthFt * windowHeightFt) * windowQuantity;
var totalObstructionAreaSqFt = doorAreaSqFt + windowAreaSqFt;
// Calculate net wall area
var netWallAreaSqFt = grossWallAreaSqFt – totalObstructionAreaSqFt;
if (netWallAreaSqFt 0) {
stripLengthFt += patternRepeatFt;
}
// Calculate total square feet of wallpaper required
var totalWallpaperSqFt = numberOfStrips * stripLengthFt;
// Convert total required square feet to square yards
var totalWallpaperSqYards = totalWallpaperSqFt / 9;
// Calculate square yards per roll using the provided roll length
// Roll width in feet = wallpaperWidth / 12
// Roll length in feet = wallpaperLength * 3 (since 1 yard = 3 feet)
// Total square feet per roll = (wallpaperWidth / 12) * (wallpaperLength * 3)
// Total square yards per roll = Total square feet per roll / 9
var sqYardsPerRoll = (wallpaperWidth / 12) * (wallpaperLength * 3) / 9;
var numberOfRolls = 0;
if (sqYardsPerRoll > 0) {
numberOfRolls = Math.ceil(totalWallpaperSqYards / sqYardsPerRoll);
} else {
// Handle case where sqYardsPerRoll is zero or invalid, though validation should prevent this
resultDisplay.textContent = "Invalid wallpaper roll dimensions.";
resultDisplay.style.color = "#dc3545″;
return;
}
// Add a buffer for waste (e.g., 10%)
var bufferPercentage = 0.10; // 10% buffer
var adjustedRolls = Math.ceil(numberOfRolls * (1 + bufferPercentage));
// Display the final result
resultDisplay.textContent = adjustedRolls + " rolls";
resultDisplay.style.color = "#28a745"; // Success green
// Optional: Display intermediate values for debugging or user clarity if needed
// console.log("Room Perimeter (ft): " + roomPerimeter);
// console.log("Gross Wall Area (sq ft): " + grossWallAreaSqFt);
// console.log("Total Obstruction Area (sq ft): " + totalObstructionAreaSqFt);
// console.log("Net Wall Area (sq ft): " + netWallAreaSqFt);
// console.log("Number of Strips: " + numberOfStrips);
// console.log("Strip Length (ft): " + stripLengthFt);
// console.log("Total Wallpaper Required (sq ft): " + totalWallpaperSqFt);
// console.log("Total Wallpaper Required (sq yards): " + totalWallpaperSqYards);
// console.log("Square Yards per Roll: " + sqYardsPerRoll);
// console.log("Number of Rolls (no buffer): " + numberOfRolls);
}