The short answer
Multiply the room length by the width, add 5 to 15% for waste depending on the material and layout, divide by the coverage printed on the box and round up. A 15 × 12 ft room is 180 sq ft; with 10% waste that is 198 sq ft, or 10 boxes of 20 sq ft each.
Measure the floor
Measure the longest length and width of the room in feet, wall to wall. Go into doorways to the point where the new floor will stop, and include a closet if the floor continues into it. For an L-shaped room, split it into two rectangles, work out each area and add them.
Floor area = length × width
How much waste to add
Waste covers the pieces you cut at walls and doorways, boards you reject and the occasional mistake. It grows with complicated rooms and with diagonal or patterned layouts, because more pieces end in angled cuts that cannot be reused. Flooring Clarity publishes these ranges by material:
| Material | Simple layout | Complex layout | Diagonal or patterned |
|---|---|---|---|
| Hardwood | 10% | 12–15% | 15% |
| Laminate | 7% | 10% | 10–12% |
| Luxury vinyl plank or tile | 5% | 7–10% | 10% |
| Ceramic or porcelain tile | 10% | 15% | 20% |
| Carpet | 5% | 7–10% | 10% |
Our flooring calculator starts at 10%, which suits a straight layout in a simple room. Raise it for a diagonal layout, a room with many corners or closets, or a product with a strong pattern you need to match.
From square feet to boxes
Boxes = floor area × (1 + waste %) ÷ coverage per box, rounded up
- Floor area: 15 × 12 = 180 sq ft.
- Add 10% for waste: 180 × 1.10 = 198 sq ft.
- Coverage per box is 20 sq ft: 198 ÷ 20 = 9.9 boxes.
- Round up: 10 boxes, which is 200 sq ft, with about 20 sq ft left over.
Use the coverage printed on the box or the product page, not a generic figure. Boxes commonly hold anywhere from about 15 to 30 sq ft depending on the product.
Tile is counted by the piece
For tile, the size of each piece matters because you buy whole tiles and whole boxes. A 12 × 12 in tile covers 1 sq ft, so a 10 × 8 ft floor needs 80 tiles before waste. At 10% that is 88 tiles; with 10 sq ft in a box, you buy 9 boxes. Diagonal layouts cut every edge tile at an angle, so the tile calculator offers a 15% preset, which gives 92 tiles and 10 boxes for the same floor.
| Project | Floor area | With waste | What to buy |
|---|---|---|---|
| 15 × 12 ft plank floor, straight lay, 10%, 20 sq ft boxes | 180 sq ft | 198 sq ft | 10 boxes |
| Same floor, diagonal layout at 15% | 180 sq ft | 207 sq ft | 11 boxes |
| 12 × 12 ft plank floor, 10%, 20 sq ft boxes | 144 sq ft | 158.4 sq ft | 8 boxes |
| 20 × 14 ft plank floor, 10%, 24 sq ft boxes | 280 sq ft | 308 sq ft | 13 boxes |
| 10 × 8 ft floor, 12 × 12 in tile, 10%, 10 sq ft boxes | 80 sq ft | 88 sq ft | 88 tiles, 9 boxes |
Buying tips
- Buy everything from the same production lot when you can. Color and shade can vary a little between lots, and a replacement box months later may not match.
- Keep the leftover boxes in a dry place. A few spare planks or tiles make a future repair easy.
- Transitions, trim, underlayment and adhesive are sold separately and are not part of the box count.
- Unopened boxes can usually be returned, but check the store policy before you buy.
Common mistakes
- Measuring only to the baseboards and forgetting closets or doorways.
- Using a generic box size instead of the one on the label.
- Skipping the waste allowance on a diagonal or herringbone layout.
- Rounding down to the nearest box.
Calculators for this job
These calculators do the arithmetic from this guide. Each card shows the result for a typical project; open one to enter your own measurements.
Frequently asked questions
How much extra flooring should I buy?
Flooring Clarity suggests about 10% for hardwood in a simple layout, 7% for laminate and 5% for luxury vinyl plank, rising to 10 to 15% or more for complex rooms, diagonal layouts and tile.
How many boxes of flooring do I need for a 12 × 12 room?
A 12 × 12 ft room is 144 sq ft. With 10% waste you need about 158.4 sq ft. At 20 sq ft per box that is 7.9 boxes, so buy 8.
How many tiles do I need for a 10 × 8 ft floor?
An 80 sq ft floor with 12 × 12 in tiles needs 80 tiles. With 10% waste that is 88 tiles, and with 10 sq ft per box you buy 9 boxes.
Should I include the closet in my measurements?
Yes, if the new floor continues into the closet. Measure it as its own small rectangle and add its area to the room.
Sources
- Flooring Clarity, How Much Extra Flooring To Buy
- Flooring Clarity, How Much Extra Tile to Buy for a Project