To work out flooring, multiply the room's length by its width, add 10% for waste, and divide by the square feet in one box. A 15 × 12 ft bedroom is 180 sq ft. With 10% waste you buy 198 sq ft, and at 23.8 sq ft per box that's 8.3 boxes, so you need 9.
Flooring is sold by the square foot, so you need the room's floor area. For a plain rectangle, that's length × width. A 15 × 12 ft bedroom is 180 sq ft.
Most rooms aren't perfect rectangles, and that's fine. A few habits keep the measurement honest:
If you already know the square footage from a floor plan, type it straight into our flooring calculator. It will skip the length and width.
You'll lose material to end cuts, pieces that don't fit the pattern and the odd damaged plank. The standard fix is a waste allowance added on top of the room's area.
| Material and layout | Common waste allowance |
|---|---|
| Vinyl plank or laminate, straight lay, simple room | 5% to 10% |
| Hardwood or engineered wood, straight lay | 10% |
| Any plank in a room with lots of angles, closets or hallways | 10% to 15% |
| Diagonal layout | 15% |
| Herringbone or chevron | 15% to 20% |
These are working rules of thumb, and the manufacturer's installation guide may say otherwise for a specific product. The calculator defaults to 10%, which suits most straight-lay jobs. The table below shows what the waste setting does to the same 180 sq ft room with boxes that cover 23.8 sq ft each.
| Waste setting | Square feet to buy | Boxes needed |
|---|---|---|
| 5% | 189 sq ft | 8 |
| 10% | 198 sq ft | 9 |
| 15% | 207 sq ft | 9 |
| 20% | 216 sq ft | 10 |
Notice that 10% and 15% give the same box count here. Because you round up to whole boxes, there's often a bit of spare built in already. It's worth trying a couple of settings before you decide.
Divide the square footage you're buying by the coverage on the box, then round up.
Boxes = room area × (1 + waste) ÷ square feet per box
For the 180 sq ft bedroom at 10% waste: 180 × 1.10 = 198 sq ft, and 198 ÷ 23.8 = 8.3, so you buy 9 boxes. Coverage per box varies a lot. It depends on the plank's width and length and on how thick it is, so always use the number printed on the box you're buying, not a typical figure.
Here's the same math for common room sizes. It uses 10% waste, 23.8 sq ft per box at $45, and rolled underlayment at $0.35 per sq ft in 100 sq ft rolls, which are the calculator's defaults.
| Room | Area | Buy (with 10%) | Boxes | Flooring cost | Underlayment |
|---|---|---|---|---|---|
| 10 × 10 ft | 100 sq ft | 110 sq ft | 5 | $225 | 2 rolls, $39 |
| 10 × 12 ft | 120 sq ft | 132 sq ft | 6 | $270 | 2 rolls, $46 |
| 12 × 12 ft | 144 sq ft | 158 sq ft | 7 | $315 | 2 rolls, $55 |
| 15 × 12 ft | 180 sq ft | 198 sq ft | 9 | $405 | 2 rolls, $69 |
| 14 × 16 ft | 224 sq ft | 246 sq ft | 11 | $495 | 3 rolls, $86 |
| 16 × 20 ft | 320 sq ft | 352 sq ft | 15 | $675 | 4 rolls, $123 |
| 20 × 24 ft | 480 sq ft | 528 sq ft | 23 | $1,035 | 6 rolls, $185 |
At $45 for 23.8 sq ft, that flooring works out to about $1.89 per sq ft, which is in the budget-to-mid range for vinyl plank and laminate. Swap in your own price per box to see your real number.
Enter the room size, waste and box coverage, add underlayment if you need it, and get boxes and material cost. Free, no signup.
Open the Flooring Calculator →It depends on the product. Laminate usually needs a foam underlayment unless the planks have a pad attached. A lot of vinyl plank comes with the pad already attached, and many makers say not to add a second layer under it. Doubling up can make the locking joints flex and fail.
Over concrete, a moisture barrier is usually required for wood and laminate. Some underlayments have one built in. Read the installation guide before you buy, because using the wrong underlayment can void the warranty.
If you do need it, underlayment covers the same area you're buying flooring for. In the calculator, untick the underlayment box if your planks already have a pad.
For floating floors, yes. Laminate, most vinyl plank and floating engineered wood need an expansion gap around the edge of the room, commonly about ¼ to ⅜ in, so the floor can move with changes in temperature and humidity. Baseboard or quarter-round covers it.
The gap doesn't change how much flooring you buy. It does mean you shouldn't cut planks tight to the wall, and it's one reason to leave the baseboards off until the floor is down. If you're painting the room while it's empty, do the walls first. The paint calculator covers gallons by room size.
Some products also need time to acclimate in the room before you install them. Solid wood and laminate usually do. Many rigid-core vinyl planks need little or none. Check the box.
Tile works differently. You count individual tiles, and you also need thinset and grout. Use the tile calculator for bathrooms, entryways or anywhere you're laying tile instead of planks.
Flooring styles are discontinued all the time, and new production runs can be a slightly different color. Keep at least one unopened box in the garage after the job. If a plank gets gouged or water-damaged, you can swap it for a perfect match.
Multiply length by width, add 10% for a straight lay (15% or more for diagonal and herringbone), and divide by the square feet on the box. Round up, buy from one lot, and hold one box back for repairs.
A 12 × 12 room is 144 sq ft. With 10% waste you should buy about 158 sq ft. At 23.8 sq ft per box that's 6.7, so 7 boxes. Use the coverage printed on your own box, since it varies by product.
Buy 5% to 10% extra for vinyl plank or laminate in a simple room, about 10% for hardwood, 10% to 15% for rooms with lots of angles, 15% for diagonal and 15% to 20% for herringbone.
Split the room into rectangles, work out length × width for each and add them together. An L-shaped room made of a 20 × 14 section and a 10 × 8 nook is 280 + 80 = 360 sq ft. Then add your waste allowance.
It depends on the plank size and thickness. Many vinyl plank and laminate boxes cover roughly 15 to 25 sq ft, but some are much smaller or larger. Always use the figure printed on the box you're buying.
Often not. Many vinyl planks come with a pad already attached, and manufacturers usually say not to add another layer on top. Planks without a pad, and laminate, usually need one. Check the installation guide for your product.