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A room that is "about 170 square feet" is how orders come up short.
A 12×14 room is 168 square feet — but flooring wants 10% waste, so you buy 184.8. At $4.29 a square foot, that is $792.79, and every project from tile to sod to paint starts with this exact number. Measure, add waste, price it — before you load the cart.
DIYers use it before the cart: 12×14 is 168 sq ft, but flooring wants 184.8 with waste — $792.79 at $4.29/ft, measured twice, ordered once.
Decompose into rectangles — every room is rectangles wearing a costume. An L-shaped room is two rectangles; measure each leg separately (say 12×14 and 6×8), compute each area (168 + 48), and add them (216 sq ft). Closets, alcoves, and bay windows are additional small rectangles to add; stairs and permanent cabinets are rectangles to subtract. For triangles (gable ends, angled walls): base × height ÷ 2. For circles (round patios, towers): π × radius². The waste factor then applies to the TOTAL, not each piece. When in doubt, sketch the floor plan and grid it — estimators who grid never reorder.
The trade standards: 10% for straight-lay plank flooring in normal rectangular rooms, 15% for diagonal layouts, herringbone, or chevron (every edge piece is an angled cut), 5–10% for tile depending on layout and tile size (large-format tile in small rooms pushes toward 15% because cuts waste more per piece), and 10–15% for patterned carpet that must match at seams. Add 5% more if the room has many corners, angled walls, or doorways. Keep one box of flooring or a few tiles after install — dye lots change, and a future repair with unmatched material is visible from space.
Useful benchmarks: bedrooms run 120–200 sq ft (a 12×12 is 144), living rooms 200–400, kitchens 150–250, and a two-car garage about 400–440. The median new US single-family home is roughly 2,200–2,300 sq ft. Note that real-estate square footage (GLA — gross living area) excludes garages, basements below grade, and unfinished spaces, and appraisers measure exterior dimensions — listing square footage and flooring square footage for the same house can differ by 10%. For material ordering, always measure the actual room; for comparing homes, always ask whether the number is GLA, total structure, or "agent optimism."