Square Footage Math for Flooring, Paint, and Tile Projects
September 18, 2026
Square footage = length × width, in feet. For irregular rooms, split the space into rectangles, calculate each separately, and add them together — then add a waste allowance before ordering material.
Skip the math and get your answer instantly:
Open the Square Footage Calculator →Handling an L-Shaped or Irregular Room
Split the room into two or more rectangles along natural break points (like an inside corner), calculate each rectangle's square footage individually, then sum them for the total. A 12×10 main area plus a 6×4 alcove: (12×10) + (6×4) = 120 + 24 = 144 square feet total.
How Much Extra to Order
| Project type | Typical waste allowance |
|---|---|
| Standard flooring (straight lay) | 5-10% |
| Diagonal or herringbone pattern | 15-20% |
| Tile with many cuts/angles | 10-20% |
| Paint (per coat) | 5-10% |
Converting Between Units
Carpet is often sold by the square yard: divide square feet by 9 (since 1 square yard = 9 square feet). For boxed flooring or tile, divide your total square footage (plus waste allowance) by the coverage listed per box, then round up to the next whole box, since partial boxes generally aren't sold.
Frequently Asked Questions
How do I calculate square footage for an L-shaped room?
Divide the room into two or more rectangles along the inside corners, calculate each rectangle's area (length × width) separately, then add the results together.
How much extra material should I order?
A common rule is 10% extra for standard installations, rising to 15-20% for diagonal patterns, herringbone layouts, or rooms with many cuts and angles.
How do I convert square feet to square yards?
Divide square feet by 9, since 1 square yard equals 9 square feet. 450 square feet ÷ 9 = 50 square yards.
Does square footage include closets and alcoves?
Include them if they'll be covered by the same material — measure and add their square footage the same way as any other section of the room.
How many boxes of flooring or tile do I need?
Divide your total square footage (plus your waste allowance) by the coverage per box listed on the product, then round up to the next whole box.