Most drywall calculators work out the total wall area, divide it by 32, and call that the sheet count. It's a quick method, but it doesn't match how boards get hung. A 12 ft wall and a 13 ft wall need different cuts, and the piece you trim off one wall can often finish the next. I wanted my estimator to plan the job the way a crew would, so it handles one wall at a time. Below is how that works, plus the formulas it uses for supplies.
Step 1: Model the room as walls, not square feet
The user gives a length, width and wall height. A rectangular room becomes four walls: two the length of the room and two the width. Each wall is a rectangle with a run (horizontal length) and a height. Doors and windows come off the area later, but for layout I treat each wall as one full rectangle first. Boards get hung over openings and the holes are cut out afterward, so that's closer to what happens on site.
Step 2: Pick a sheet and fill each wall
Sheets come in 4 ft widths and lengths of 8, 9, 10 or 12 ft. Hanging them horizontally, I work out how many rows the wall height needs and how many sheet lengths fit along the run. The leftover at the end of each row is the useful part, because that's what turns into an offcut.
function layoutWall(run, height, sheetLen, offcuts) {
const rows = Math.ceil(height / 4);
let sheets = 0;
for (let r = 0; r < rows; r++) {
let remaining = run;
// reuse the biggest offcut that fits first
offcuts.sort((a, b) => b - a);
const i = offcuts.findIndex(o => o <= remaining && o >= 2);
if (i !== -1) remaining -= offcuts.splice(i, 1)[0];
while (remaining > 0) {
sheets++;
if (remaining < sheetLen) offcuts.push(sheetLen - remaining);
remaining -= sheetLen;
}
}
return sheets;
}
The offcuts array is shared across all the walls, so a 4 ft scrap from the first wall can complete a row on the third. I skip anything under 2 ft, since tiny scraps add extra joints and nobody wants to tape them. This is the step that brings the count below the plain area-based estimate.
Step 3: Add spare
Once every wall is laid out, the planner adds 10% and rounds up. Sheets crack, corners get dinged, and someone always mis-measures an outlet box. The spare is shown separately, so you can see what's laid out and what's extra.
Step 4: Deduct openings for materials
Openings matter for finishing supplies even though boards cover them during hanging. I use standard deductions: 21 sq ft per door, 15 per window and 112 per garage door. The net area that's left drives all the material formulas.
Step 5: Material formulas
These are rules of thumb, scaled to the net area:
- Joint compound: about 140 lb per 1,000 sq ft. A 4.5 gallon box of premixed mud weighs roughly 61.7 lb, so the app turns pounds into boxes.
- Tape: about 370 ft per 1,000 sq ft, rounded up to whole rolls.
- Screws: roughly 1 per sq ft on walls and 1.25 per sq ft on ceilings, since ceilings need closer spacing.
- Cost (optional): enter a unit price for each item and you get a line-item total.
A worked example
Take a 14 x 12 ft room with 8 ft walls, one door and two windows. Gross wall area is 2 x (14 + 12) x 8 = 416 sq ft. Taking off 21 for the door and 30 for the windows leaves 365 sq ft net. Laid out wall by wall with offcuts reused, the plan uses 13 sheets. Adding 10% spare and rounding up gives 15 to buy.
Why client-side only
Everything above runs in plain JavaScript in the browser. There's no backend, no account and nothing stored on a server. That keeps it fast, makes it work on a phone in a half-finished basement, and means it can be embedded on another site with a single iframe. It also handles feet and inches or metric, converting to a common unit before running the layout.
If you'd like to try it or poke at the results, the live version is at Drywall Planner. I'd like to hear how others have handled cut-list or bin-packing problems like this, especially smarter offcut matching than a greedy pass.
