How to calculate flooring
Find the room area, add a waste allowance for cuts, then divide by the coverage of a single box and round up — you can only buy whole boxes:
Boxes = (Floor area × (1 + waste %)) ÷ Coverage per box
A 12 × 15 ft room is 180 sq ft. With 10% waste that's 198 sq ft, and at 20 sq ft per box you need 198 ÷ 20 = 9.9, rounded up to 10 boxes.
How much waste to add
- Straight lay: 10% is the standard allowance.
- Diagonal or herringbone: 15% — angled cuts waste more.
- Lots of closets, jogs, or angles: lean toward 15%.
Buy every box at once so the planks share a dye lot, and keep one spare box for repairs down the road.
Don't forget underlayment
Floating floors usually need an underlayment unless it's pre-attached. It's sold by the roll in square feet, so size it from the room area — no waste allowance needed since it isn't cut plank by plank.
Frequently asked questions
How do I calculate how much flooring I need?
Find the room area by multiplying length × width, add a waste allowance for cuts, then divide by the square footage one box covers and round up. A 12 × 15 ft room is 180 sq ft; with boxes covering 20 sq ft and 10% waste, you need about 10 boxes.
How much extra flooring should I buy for waste?
Add about 10% for a standard straight installation, and 15% for diagonal or herringbone layouts or rooms with many angles and closets. Buy it all at once so the planks share a dye lot and pattern run, and keep a spare box for future repairs.
How many square feet are in a box of flooring?
It varies by product and plank size, so check the label — common laminate and vinyl boxes cover roughly 18 to 24 square feet, while hardwood boxes are often around 20 sq ft. Enter the exact coverage from your box for an accurate box count.
Should I subtract closets, islands, or cabinets?
Add the floor area of closets and bays you are flooring, and subtract permanent fixtures like kitchen islands or cabinet runs that sit on the subfloor. For an irregular room, split it into rectangles, find each area, and add them together.
Do I need underlayment too?
Many floating floors (laminate and some vinyl) need an underlayment unless it is pre-attached to the planks. Underlayment is sold by the roll in square feet, so size it from the same room area — without the waste allowance, since it is not cut to fit each plank.
Disclaimer: Results are estimates for planning. Confirm the exact coverage printed on your flooring boxes and buy a little extra for cuts and future repairs.