Paint Calculator
Calculate how many gallons of paint you need for any room or surface.
The Formula
Coverage ≈ 350–400 ft² per gallon
Wall area = perimeter × height − doors/windows
Wall area = (2×12 + 2×14) × 9 = 468 ft²
Less 2 doors (40 ft²) = 428 ft²
428 × 2 coats / 350 = 2.45 → 3 gallons
How Much Paint Do You Need?
One gallon of paint typically covers 350–400 square feet per coat on smooth, previously painted surfaces. To calculate wall area for a room: add up all wall lengths to get the perimeter, multiply by ceiling height to get total wall area, then subtract about 20 square feet per standard door and 15 square feet per window. Divide the net wall area by 350 to get gallons needed per coat. Always buy 10–15% more than your calculation suggests to account for touch-ups, uneven surfaces, and future repairs.
One Coat or Two?
How many coats you need depends on color and surface conditions. Painting a similar color over an existing coat often requires just one coat of quality paint. Going from dark to light — or light to dark — almost always requires two coats for full coverage. Fresh drywall and bare wood are thirsty surfaces that absorb the first coat heavily and typically require two coats no matter the color. Self-priming paints can save a step on previously painted surfaces, but bare surfaces almost always benefit from a dedicated primer coat first.
Sheen Matters More Than Most People Think
Paint sheen (flat, eggshell, satin, semi-gloss, gloss) affects both appearance and durability. Flat/matte hides imperfections best and works well for ceilings and low-traffic walls, but it scuffs and does not wipe clean easily. Eggshell and satin offer a gentle sheen with better washability and are the most popular choice for living rooms and bedrooms. Semi-gloss and gloss are durable and moisture-resistant — ideal for trim, doors, kitchens, and bathrooms where frequent cleaning is needed.
Frequently Asked Questions
How much does a gallon of paint cover?
Most paints cover 350–400 square feet per gallon on smooth surfaces. Textured walls, bare wood, and masonry absorb significantly more paint and may only yield 200–300 square feet per gallon. Always use the lower end of coverage estimates when calculating to avoid running short.
Should I buy gallons or quarts?
For large surfaces like walls and ceilings, gallons are far more economical — typically $30–55 per gallon vs. $12–20 per quart. Quarts make sense for small accent walls, trim, or touch-up work. If you only need to cover a small area (under 100 square feet), a quart is sufficient and more practical.
Do I need primer?
Primer is strongly recommended for bare drywall, bare wood, stain-blocking, or when making a dramatic color change. Self-priming paints (paint and primer in one) work adequately for repainting similar colors on previously painted surfaces. For best adhesion and coverage on new construction or repaired surfaces, a separate primer coat is worth the time and cost.
How long should I wait between coats?
Most latex paints are dry to the touch in 1–2 hours and can receive a second coat in 4–6 hours. Oil-based paints take 6–8 hours between coats. For best results, wait at least 4 hours even for fast-dry latex. Painting a second coat too early traps moisture and can cause peeling or texture problems.
How do I calculate paint for ceilings?
Ceiling area is simply length times width of the room. A standard 10x12 foot bedroom ceiling is 120 square feet — well under one gallon. Most ceilings need only one coat of ceiling paint unless you are covering a stain or significant color change. Flat white ceiling paint is standard and typically less expensive than wall paint.