How Much Paint Do I Need?
Enter your room dimensions and paint type to get exact gallons — walls, ceiling, and trim. Coverage rates vary significantly by paint type: chalk paint covers far less than latex, so paint type matters here.
How to calculate how much paint you need
The formula: measure each wall's width × ceiling height. Add all four walls, then subtract 21 sq ft per door and 15 sq ft per window. Divide by your paint's coverage rate and multiply by the number of coats. Always round up to the nearest gallon.
For a typical 12×12 ft bedroom with 8-ft ceilings, one door, two windows: (4 × 12 × 8) − 21 − 30 = 333 sq ft net wall area. At 350 sq ft/gal × 2 coats = 1.9 gallons. Buy 2 gallons — which gives a small touch-up buffer.
Paint coverage rates by type — why type matters
Latex / acrylic: 350–400 sq ft/gal on smooth, previously painted walls. The most common interior paint. Premium formulas with higher pigment density approach 400 sq ft/gal. Standard formulas are closer to 350 in real-world conditions.
Chalk paint: Only 150–200 sq ft/gal. Chalk paint's high calcium carbonate content gives it that flat, porous look — but the same property makes it less opaque per coat. Plan for 2–3 coats and add a wax or polycrylic topcoat budget. Some brands like Annie Sloan achieve better coverage per gallon than cheap chalk paint alternatives.
Oil-based paint: 300–350 sq ft/gal. Similar to latex but applied thinner. Oil-based paints are typically reserved for trim, cabinets, and high-wear surfaces because of their hardness and long cure time — rarely used on walls anymore due to VOCs and long dry times.
Primer: 250–350 sq ft/gal depending on type. Drywall primer (PVA) goes further. Stain-blocking primers (shellac-based or oil-based) cover less and cost more. Textured wall primer covers even less.
Textured walls: Any paint on a textured surface (orange peel, skip trowel, knockdown) covers 15–25% less than on a smooth surface. Add extra if your walls have heavy texture.
Do I need primer — and how much?
Primer is required when painting bare drywall (always), covering a dramatic color change (especially dark to light), painting over stains, water damage, or smoke, or painting over glossy surfaces. For a standard repaint in a similar color, a quality paint-and-primer-in-one formula is sufficient and saves you a step.
Primer coverage rate is about 300 sq ft/gal for standard drywall primer, 250 sq ft/gal for stain-blocking. One primer coat is usually enough — the goal is sealing the surface, not color uniformity.