How the flooring math works
Floor area × (1 + waste %) = square feet to buy
Square feet to buy ÷ coverage per box = boxes (rounded up)
Square feet to buy ÷ coverage per box = boxes (rounded up)
Worked example
A 15 × 12 ft room is 180 sq ft. With 10% waste you need 198 sq ft. At 22.5 sq ft per box that’s 8.8, so buy 9 boxes (202.5 sq ft).
Choosing a waste allowance
| Layout | Typical allowance |
|---|---|
| Straight lay, simple rectangular room | 5–10% |
| Rooms with many corners, closets or doorways | 10–15% |
| Diagonal, herringbone or patterned layouts | 15–20% |
Check before you buy: manufacturers sometimes specify their own waste figure, and some warranties require a minimum. Buy every box from the same production lot where possible, and keep a spare box for future repairs.
Common questions
How much extra flooring should I buy?
About 10% for a straight layout in a simple room, and 15% or more for diagonal or patterned layouts, rooms with lots of cuts, or tile that breaks easily.
Do I include closets?
Yes, if the flooring runs into them. Add each closet as its own area.
Should I subtract kitchen islands or built-ins?
Only if the flooring won’t go under them. Many installers floor under cabinets that might move later. Leave fixed islands out.
Can I return unopened boxes?
Many stores accept returns of unopened boxes, but policies differ. Check before buying extra.
Related calculators
See how we calculate for every formula and constant used on this site.