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Room Area: Rectangles, L-Shapes and the Waste Rule

Home & Garden · 5 min read · Last updated September 2026

Quick answer: Rectangles are length × width; anything else decomposes into rectangles (or circles for rugs). A 12×15 ft room is 180 sq ft; an 80 sq ft rug covers 44.4% of it. Material orders then add a waste allowance — 10% is the honest default.

The shapes that cover real floors

Rectangle: L × W · Circle: π r² · L-shape: split into two rectangles, add

Worked example: a 12 × 15 ft room = 180 sq ft. A rug of 80 sq ft covers 80 ÷ 180 = 44.4% of the floor. An L-shaped living room is just two rectangles: 12×15 plus 8×6 = 180 + 48 = 228 sq ft. Measure to the finished wall surface, not the skirting.

From area to material order (the waste %)

Material	Waste allowance	Why
Tile (straight lay)	+10%	Cuts, breakage, future repairs
Tile (diagonal)	+15%	More edge cuts
Wood flooring	+7–10%	Board-length staggering
Carpet (broadloom)	+10–20%	Seam placement, nap direction

Ordering exactly 180 sq ft of tile for a 180 sq ft floor is how projects end one box short. The Room Area & Flooring Calculator adds waste automatically; Area Converter handles sq ft ↔ sq m, and Paint Estimator does the same math vertically for walls.

Try the calculators

Frequently asked questions

How do I calculate the area of a room?

Multiply length by width for rectangles. L-shaped rooms split into two rectangles and add. A 12×15 ft room is 180 sq ft.

How do I calculate area of an irregular room?

Decompose into rectangles (and circles for curves), compute each, then add. Sketch the floor plan with dimensions — five minutes of measuring beats guessing.

How much extra material should I order?

10% waste is the standard default: 7–10% for wood, 10–15% for tile (more if diagonal), 10–20% for carpet. Diagonal layouts and pattern repeats push higher.

How do I convert square feet to square meters?

Divide sq ft by 10.764. A 180 sq ft room is about 16.7 sq m. The Area Converter does all direction conversions precisely.