How to calculate flooring
Flooring is priced per square foot but sold by the box, so there are three numbers to get right: the floor area, the extra you need for cuts and waste, and how many whole boxes that adds up to.
Start with length × width for each rectangular space. If the room is L-shaped or you're running the floor into a closet or hallway, tick "Add more areas" and enter each rectangle separately; the calculator adds them. Then it applies a waste factor based on the layout, divides by the coverage printed on the box, and rounds up.
Waste factors by pattern
| Layout | Waste allowance | Why |
|---|---|---|
| Straight (parallel to a wall) | 10% | End cuts, damaged pieces, trimming around doorways |
| Diagonal (45°) | 15% | Every row starts and ends with an angled cut |
| Herringbone / chevron | 20% | Short pieces and angled perimeter cuts throughout |
These are the allowances most manufacturers and flooring retailers recommend. Add 2–5% more for rooms with lots of corners, a fireplace hearth or angled walls, or for tile with a large repeating pattern.
The formula
area with waste = floor area × (1 + waste %)
boxes = area with waste ÷ sq ft per box, rounded up
flooring cost = boxes × sq ft per box × price per sq ft
Example: a 12 × 15 ft bedroom with a straight layout
| Step | Result |
|---|---|
| Floor area (15 × 12) | 180 sq ft |
| Plus 10% waste | 198 sq ft |
| Boxes (198 ÷ 20 = 9.9) | 10 boxes |
| Boxes cover | 200 sq ft |
| Flooring cost (200 × $3.50) | $700.00 |
With underlayment added, the same room needs 2 rolls of 100 sq ft (underlayment isn't cut to a pattern, so it uses the floor area without waste), adding $60 at $30 a roll for a total of $760.
The $3.50 default is typical of mid-range laminate or luxury vinyl plank. Budget laminate runs about $1–$2 per sq ft, engineered hardwood $4–$9, and solid hardwood $5–$12, before installation.
Tips before you buy
- Check the box, not the product page. Coverage varies a lot: vinyl plank cartons often hold 18–24 sq ft, laminate 14–25, and tile is frequently sold by the individual piece or smaller cartons.
- Buy one lot. Make sure every box has the same lot or run number so the color matches, and open several boxes at once while installing to blend any variation.
- Keep a spare box. Leftover planks are the easiest way to repair water damage or a deep scratch years later, when the product may no longer be made.
- Acclimate first. Laminate and wood usually need 48 hours in the room before installation.
- Mind the pad. Many vinyl planks have attached underlayment; adding more can void the warranty. Over concrete, laminate needs a vapor barrier.
- Budget for transitions. Thresholds, reducers and quarter-round are sold separately, usually by the linear foot or piece.
Frequently asked questions
How much extra flooring should I buy?
Buy about 10 percent extra for a straight layout, 15 percent for a diagonal layout, and 20 percent for herringbone or chevron. Rooms with many corners, closets or angled walls may need a few percent more. Keep a spare box or two for future repairs, since the same product may be discontinued.
How do I calculate square footage for flooring?
Multiply the length by the width of the room in feet. For an L-shaped room, split it into two rectangles, calculate each one, and add them together. Include closets and any area under appliances you plan to floor.
How many boxes of flooring do I need?
Divide the square footage including waste by the square feet per box printed on the carton, then round up. A 12 by 15 foot room is 180 square feet, 198 with 10 percent waste, which is 10 boxes of 20 square feet each.
Do I need underlayment for laminate or vinyl plank?
Laminate almost always needs a foam underlayment, and a vapor barrier over concrete. Many vinyl plank and some laminate products come with a pad already attached, in which case extra underlayment can void the warranty. Check the product's installation instructions.
Should I round up to a full box?
Yes. Stores sell flooring by the box, and many accept returns of unopened boxes, so buying one more than you need is cheaper than a second trip or running out mid-install. Buy all boxes from the same production lot so color and texture match.
Rates and figures last checked September 2026.
This calculator gives estimates for planning. Check current rates and product labels before you buy, list or file.