How Much Paint Do I Need For A Room?
QUICK ANSWER
Standard coverage: 1 gallon covers about 350 square feet (single coat). For a 12x12 room with 8-foot walls (384 sq ft of walls), you need about 2 gallons for two coats. Add 10% for waste. Textured walls and dark colors over light typically need more (1.5x standard). Subtract windows and doors.
Buying too little paint means rushing back to the store; buying too much wastes money and creates storage problems. The standard 350 sq ft per gallon coverage figure is optimistic; texture, surface absorption, color change, and application method all affect actual coverage. Knowing how to calculate accurately saves money and frustration. Here is the calculation plus the factors that change the answer.
How do you calculate wall area?
Basic math first. For each wall: length x height. Add four walls together. A 12x12 room with 8-foot ceilings: 384 sq ft of wall area. A 14x10 room with 9-foot ceilings: 432 sq ft. Subtract windows (~12 to 15 sq ft each) and doors (~21 sq ft each). For ceilings: length x width; a 12x12 ceiling is 144 sq ft.
What about coverage realities?
Standard claims vs reality. Most manufacturers state 350 to 400 sq ft per gallon for one coat on smooth surfaces. Real-world: smooth previously-painted walls (350 to 400 sq ft, matches claim); textured walls (250 to 300 sq ft); porous surfaces like raw drywall (200 to 300 sq ft). Dark color over light may need 2 to 3 coats. Bold colors often need 3 coats. Tinted primer reduces topcoats. Premium paints cover better in fewer coats than cheap paints.
How many coats and how much for the full job?
Multi-coat calculations. Most paint jobs need 2 coats; even paint+primer-in-one. Two coats doubles the paint needed. For our 384 sq ft room with 2 coats: 768 sq ft needed; at 350 sq ft per gallon, that's 2.2 gallons; at realistic 280 sq ft for textured walls, 2.7 gallons. Round UP and add 10% for waste. Realistically buy 3 gallons. Ceilings and trim need separate calculations; trim paint covers 75 to 100 linear feet of baseboards per quart.
What about touch-ups and storage?
Plan for the future. Buy slightly more than calculated needs (10% extra); having leftover paint for touch-ups is essential. The wall color you painted will change slightly over time due to UV exposure, dirt accumulation, and oxidation; touch-up paint from the original can usually matches reasonably well within the first year, less so afterward. Label all paint cans with the date painted and what room; you'll thank yourself when touch-ups are needed years later. Store leftover paint properly (see separate article on paint storage). For very large jobs (whole house exterior, multiple rooms): consider buying 5-gallon buckets instead of individual gallons; saves money per gallon; allows consistent color across the project (slight variation between cans is common; buckets ensure consistency). Many paint manufacturers offer paint calculators on their websites that estimate based on room dimensions; useful for verification.
Paint quantity calculation balances optimistic coverage claims against real-world factors (texture, color change, surface absorption). The 350 sq ft per gallon figure is a starting point; adjust based on the specific situation. Always buy slightly more than needed to allow for waste and future touch-ups; storage of leftover paint is much easier than running out mid-job. For complex projects (multiple colors, accent walls, ceiling vs walls), calculate each separately. Paint manufacturer calculators (Sherwin-Williams, Benjamin Moore, Behr all offer online calculators) provide additional verification.
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