How to measure a room for flooring
Measure the length and width at the widest points and multiply. For irregular rooms, divide the floor into rectangles, measure each, and add the areas together. Include closets and the space under doors if the flooring will run through them.
How much extra flooring should I buy?
Plank flooring needs extra for end cuts, damaged boards and pattern matching. 10% is the usual recommendation. Use 5% only for very simple rectangular rooms, and 15% for diagonal layouts or rooms with lots of corners and doorways.
Where do I find the coverage per box?
It's printed on the box and in the product description – for example "20.06 sq ft per carton" or "2.13 m² per pack". Coverage varies a lot between products, so always use the exact number.
Example: 14×12 ft bedroom
168 ft² + 10% waste = 184.8 ft². With boxes covering 20 ft² each, you need 10 boxes.