Calculating paint seems simple—measure the walls and buy the paint—but professional results require a bit more math. The "spread rate" of paint varies by brand and surface texture, and failing to account for multiple coats is the most common DIY mistake.

The Golden Rule: 350-400 Sq Ft

A standard gallon of high-quality interior latex paint typically covers 350 to 400 square feet with a single coat.

Always round up to the nearest quart or gallon. It's better to have leftover paint for touch-ups than to run out mid-wall, which can lead to visible "lap marks" when you restart.