How the flooring calculator works
Flooring is sold by the box, and each box covers a fixed number of square feet. The calculator adds your room sections, adds extra for cutting, and rounds up to whole boxes.
Area to buy = room area × (1 + waste %)
Boxes = area to buy ÷ square feet per box, rounded up
Underlayment rolls = room area × 1.05 ÷ square feet per roll, rounded up
Trim pieces = trim length × 1.10 ÷ 8 ft, rounded up
Worked example
A 15 by 12 foot living room is 180 sq ft. With 10% extra you need 198 sq ft, so 10 boxes of 20 sq ft (200 sq ft). Underlayment needs 189 sq ft, or 2 rolls of 100 sq ft. 48 feet of quarter-round with 10% extra is 7 pieces of 8 feet.
Measuring a room for flooring
- Measure the longest length and width wall to wall, into door openings where the floor will run.
- Include closets you are flooring as their own sections.
- Subtract islands, built-in cabinets and fireplace hearths with a cut-out section.
- For open-plan spaces, split the floor into rectangles and add them together.
Waste allowance by layout
| Layout | Typical extra |
|---|---|
| Straight, simple rectangular room | 5 to 10% |
| Straight, many corners or closets | 10 to 15% |
| Diagonal | 15% |
| Herringbone | About 20% |
Laminate, vinyl plank or hardwood
| Type | Underlayment | Good to know |
|---|---|---|
| Laminate | Usually needed; vapor barrier over concrete | Not for wet areas unless rated waterproof |
| Vinyl plank (LVP) | Often built in; check before adding one | Good for kitchens and basements |
| Engineered hardwood | Depends on install method | Can float, glue or nail down |
| Solid hardwood | Felt or paper underlay when nailed | Not over concrete without a subfloor |
Before you buy
- Buy all boxes from the same production lot so color and texture match.
- Leave the boxes in the room for the acclimation time the manufacturer lists before installing.
- Floating floors need an expansion gap at the walls, which the trim covers. Do not skip the trim.
- Keep one spare box for future repairs.
Common questions
How much extra flooring should I buy?
About 10% for a straight layout, 15% for diagonal and around 20% for herringbone. Rooms with many corners, closets or doorways need more cuts and should use the higher figure.
How many boxes of flooring for a 12x12 room?
A 12 by 12 foot room is 144 sq ft. With 10% extra you need 158.4 sq ft. At 20 sq ft per box that is 8 boxes.
Do I need underlayment for vinyl plank?
Many vinyl plank products have a pad attached and say not to add another one. Laminate and floating wood floors usually need underlayment, and a vapor barrier over concrete. Follow the product's installation guide.
Should flooring go under kitchen cabinets?
Floating floors such as laminate and most vinyl plank should not be pinned under heavy cabinets or islands, because they need room to expand. Measure only the open floor and subtract the island with a cut-out section.
How do I measure for baseboard or quarter-round?
Add the lengths of all walls in the room and subtract door openings. The calculator converts that into 8 foot pieces with 10% extra for corner cuts.