Paint Coverage Calculator – Get the Right Amount Every Time
Know how much paint you need before you open a single can.
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How Much Paint Do You Really Need?
Standard calculators assume a perfect rectangle. That's fine if you're painting a shoebox. But most rooms aren't that simple. When I moved last year, I made this exact mistake — I bought 4 gallons for a 12x15 room based on a basic online tool. Ended up with a full gallon leftover. That's $35 down the drain. This calculator accounts for L-shaped rooms, window and door deductions, and surface porosity. For interior latex paint, you typically get 350-400 sq ft per gallon. Primer covers less: 300-350 sq ft per gallon. Exterior latex lands in the same ballpark at 300-400 sq ft per gallon. Fresh drywall? That sucks up more paint. The calculator adds a 20% buffer automatically. Just tell it you're painting new drywall.
Paint Coverage by Type
Here's how much one gallon covers. Use this as a quick cheat sheet, but honestly, just trust the calculator to be right.
Why Most Calculators Fall Short
Honestly, this won't work if your walls are heavily textured — like popcorn or orange peel. Those surfaces can reduce coverage by 15-25%. But for flat or lightly textured walls, our tool is spot-on. The biggest complaint we hear: "My room isn't a rectangle." So we built in L-shape support. Just input each section separately. The calculator sums the area and accounts for corners. Another pain point: porous surfaces. Fresh drywall, unpainted plaster, or old wallpaper residue. Standard tools ignore this. Ours doesn't. You'll see a toggle for "Porous Surface" — flip it on and coverage drops by 20%. Prices range from $15 to $70 per gallon, with typical cans costing around $35. Use the calculator to estimate your cost, then check the brand recommendations below.
CoverWise vs. Standard Calculators
We tested five popular paint calculators. Here's how CoverWise stacks up.
How to Use the Calculator (Step by Step)
First, measure your room. Length, width, and height in feet. Our typical room is 12 ft wide, 15 ft long, and 8.5 ft high. But yours might be different — that's fine. Second, count your windows and doors. Each window saves about 15 sq ft. Each door saves 20 sq ft. Third, select your paint type: interior latex, exterior latex, or primer. Fourth, toggle "Porous Surface" if you're painting new drywall or unpainted walls. Fifth, hit calculate. The tool spits out gallons needed, plus a cost range. Simple. In my experience, most 12x15 bedrooms need 2 gallons for two coats. But run the numbers — don't guess.
Frequently Asked Questions
CoverWise Pick•Our Recommendation
CoverWise Pick: Sherwin-Williams Duration Interior Paint
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Frequently Asked Questions
- How many gallons of paint do I need for a 12x12 room?
- A 12x12 room with 8-foot ceilings has about 384 sq ft of wall space. After subtracting windows and doors (~20 sq ft), you need about 1 gallon per coat. For two coats (recommended), buy 2 gallons. Use our calculator above for precise numbers based on your exact room dimensions.
- Does paint coverage vary by brand?
- Yes. Most quality paints cover 350-400 sq ft per gallon, but some premium paints thin to 250-300 sq ft for better hide. Always check the can label — coverage is listed in sq ft per gallon. Our calculator lets you adjust coverage rate for your specific paint.
- Why do I need two coats of paint?
- One coat rarely provides even coverage, especially over patched walls or color changes. The first coat seals and primes; the second coat gives uniform color and durability. The only exception: painting the same color over the same color in good condition.
- Should I subtract windows and doors from my wall area?
- Yes, but don't over-subtract. Standard windows average 15 sq ft, standard doors 21 sq ft. Subtract them from your total, but keep 5-10% extra paint for touch-ups. Our calculator includes this buffer automatically.
- Is this paint calculator really free? No email required?
- Yes. 100% free. No email, no signup, no paywall. Get your paint estimate instantly.
- What if I'm painting over a dark color with a light color?
- Add an extra coat. Dark-to-light transitions almost always need 3 coats: primer + 2 finish coats. Use a high-hide primer (gray or white) to reduce the number of finish coats needed.
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