This gets you a budget number in about ten minutes. It does not replace a measured estimate, and the last section explains why.
The basic calculation
- Measure the room’s length and width in feet, wall to wall.
- Multiply them. A 12 × 14 room is 168 square feet.
- Add the waste factor: 10% for straight-laid plank or carpet, 15% for diagonal or herringbone.
- 168 × 1.10 = 185 square feet to buy.
Measure at the widest points, and measure into doorways and closets if you are flooring them.
Rooms that are not rectangles
Split the room into rectangles. Measure each one, calculate its square footage, add them together, then apply the waste factor to the total.
For a bay window or an angled corner, measure it as the rectangle it would be if the wall were straight. You will buy slightly too much, which is the correct error to make.
Why the waste factor is not optional
Planks get cut at every wall, and the offcut is only reusable if the next row happens to need that exact length. It usually does not. Ten percent is the industry standard for a straight layout and it is not padding.
Diagonal and herringbone patterns waste more because nearly every cut is an angle, hence 15%.
Buy the extra in the same run anyway. Dye lots vary between production runs, and a plank from a different lot two years later will not match. Keep the leftovers.
Stairs
Stairs are not measured in square feet. They are priced per tread, because each one is a separate cut-and-wrap job. Count your treads and ask for a per-tread price.
Why our number will differ from yours
An installer measuring the same room will usually come back with a figure a little different from yours, for reasons that are not padding:
- Seam planning. On carpet especially, where the seams fall determines how much of the roll is usable. A room might need a wider cut than its dimensions suggest.
- Roll and plank widths. Carpet comes in 12-foot and 15-foot widths. A 13-foot room off a 12-foot roll means a seam, or a 15-foot roll with real waste.
- Direction. Which way the plank runs changes the cut pattern and the waste.
- Transitions. Where the new floor meets an existing one needs a threshold, which is priced separately.
Use your number to know whether you are looking at a $900 room or a $2,400 room. Use a measured estimate to decide.