Calculate Wallpaper Rolls with JavaScript

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How to Calculate How Much Wallpaper You Need (Without Running Short)

Hanging wallpaper is expensive. If you don't account for the pattern repeat, you'll end up one roll short with a wall half-finished. Let's look at how to automate the calculation using JavaScript. The Math (Step-by-Step) Calculate the Drops Needed: Wall Width (inches) ÷ Roll Width (inches) = Number of Drops (Round up to the nearest whole number) Calculate the Cut Length: Wall Height (feet) + Pattern Repeat (feet) = Cut Length per Drop Calculate Drops per Roll: Roll Length (feet) ÷ Cut Length (feet) = Drops per Roll (Round down, because you can't use leftover scraps) Calculate Total Rolls: Total Drops Needed ÷ Drops per Roll = Total Rolls (Round up to the nearest whole roll) The JavaScript Solution Here is how you write a function to do this automatically, including converting the pattern repeat from inches to feet: function calculateWallpaper(wallWidthFt, wallHeightFt, rollWidthIn, rollLengthFt, patternRepeatIn) {
// 1. Total drops needed
const wallWidthIn = wallWidthFt * 12;
const dropsNeeded = Math.ceil(wallWidthIn / rollWidthIn);

// 2. Cut length per drop (wall height + pattern repeat)
const patternRepeatFt = patternRepeatIn / 12;
const cutLength = wallHeightFt + patternRepeatFt;

// 3. Drops per roll
const dropsPerRoll = Math.floor(rollLengthFt / cutLength);

// 4. Total rolls
if (dropsPerRoll === 0) {
throw new Error("The wall is too tall for this roll length.");
}

const totalRolls = Math.ceil(dropsNeeded / dropsPerRoll);

return {
dropsNeeded,
cutLength,
dropsPerRoll,
totalRolls
};
}

// Example: 10ft wide, 8ft high wall. 20.5in wide, 33ft long roll. 24in repeat.
const result = calculateWallpaper(10, 8, 20.5, 33, 24);
console.log(You need ${result.totalRolls} rolls.);
// Output: You need 2 rolls.
Common Gotchas Pattern Matching: If you have a "straight match" (like a checkerboard), you need exactly one full pattern repeat added to your cut length. If you have a "drop match" (like a diagonal pattern), you might need to add two repeats to alternate drops. Waste Factor: The Math.ceil() ensures you have enough rolls, but you should always buy one extra roll. It is much easier to return an unopened roll than to order more from the same dye lot later. Doors and Windows: If you have windows or doors, subtract their square footage from the total wall area before calculating drops to avoid buying too much paper. The Visual Way Trying to calculate drops, pattern repeats, and waste across multiple walls is a massive headache. If you want to determine the exact number of rolls required based on wall dimensions and pattern repeat drop distances, I built a free Wallpaper Roll Estimator. Try it here 100% client-side. Nothing uploaded. Have you ever underestimated a wallpaper project? Let me know in the comments.

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